I 


A  TREATISE 


ON 


ROADS  AND  PAVEMENTS. 


BY 

IRA  OSBORN  BAKER,  C.  E.,   D.  Eng'g, 

Professor  of  Civil  Engineering,  University  of  Illinois ;  Author  of  Masonry  Construction 

Engineer's  Surveying  Instruments;  Member  of  American  Society  of 

Civil  Engineers,  Western  Society  of  Engineers,  Society 

for  Promotion  of  Engineering  Education. 


FIRST  EDITION. 
ELEVENTH    THOUSAND. 


NEW  YORK: 

JOHN  WILEY  &  SOISTS. 

London:    CHAPMAN  &  HALL,   Limited. 

1913 


a 


/ 


Copyright,  1908, 

BY 

IRA  OSBORN  BAKER. 


THE   SCIENTIFIC    PRESS 

ROBERT    DRUMMOND    AND    COMPANY 

BROOKLYN,    N.    Y. 


PEEFACE. 


The  object  of  this  book  is  to  give  a  discussion  from  tlie  point  of 
view  of  an  engineer  of  the  principles  involved  in  the  construction  of 
country  roads  and  of  city  pavements.  The  attempt  has  been  made 
to  show  that  the  science  of  road  making  and  maintenance  is  based 
upon  well-established  elementary  principles,  and  that  the  art  de- 
pends upon  correct  reasoning  from  the  principles  rather  than  in 
attempting  to  follow  rules  or  methods  of  construction.  In  some 
cases  practical  experience  has  not  yet  determined  the  best  method 
of  procedure,  and  in  these  cases  the  conflicting  views  with  the 
reasons  for  each  are  fully  stated. 

Considerable  space  has  been  given  to  the  economics  and  location 
of  country  roads  and  to  the  construction  and  maintenance  of  earth 
roads,  since  such  roads  constitute  more  than  ninety-five  per  cent  of 
the  mileage  of  the  public  highways  and  are  greatly  in  need  of  care- 
ful consideration.  It  is  frequently  claimed  by  engineers  that  the 
public  would  be  benefited  by  placing  the  care  of  the  roads  in  the 
hands  of  engineers;  but  there  is  no  evidence  that  any  considerable 
number  of  engineers  comprehend  either  the  principles  of  road 
making  necessary  for  the  improvement  and  maintenance  of  our 
country  roads,  or  the  economic  limitations  and  political  difficulties 
of  the  problem.  The  first  four  chapters  of  this  book  are  offered  as 
a  contribution  to  this  phase  of  the  good-road  problem. 

The  remainder  of  the  book,  the  portion  that  considers  roads 
having  permanently  hard  surfaces,  which  may  not  unfittingly  be 
said  to  relate  to  urban  and  suburban  roads,  is  based  chiefly  upon 
American  experience,  because  the  principles  of  road  making  worked 
out  in  this  country  are  probably  best  suited  to  American  conditions, 
and  also  because  in  most  particulars  American  roads  and  pave- 
ments are  superior  to  any  other  in  the  world.     Some  countries 


265946 


IV  PREFACE. 

have  more  hard  roads  than  this,  because  of  a  difference  in  condi- 
tions; but  in  no  country  does  the  quality  of  such  roads  average 
better  than  in  this.  In  some  foreign  cities  the  pavements  seem  to 
be  better  cared  for  than  in  this  country,  owing  chiefly  to  different 
controlling*  conditions ;  but  the  principles  of  construction  employed 
here  are  equal  to  the  best.  Notwithstanding  the  general  excellence 
of  the  best  American  practice  in  constructing  hard  roads  and  pave- 
ments, theie  is  still  room  for  improvement  in  adapting  the  particu- 
lar form  of  construction  to  the  local  conditions  and  also  in  pre- 
serving the  surface  from  ruthless  destruction.  These  two  phases 
of  the  subject  have  been  emphasized  in  the  proper  places  in  this 
volume.  Throughout  the  attempt  has  been  to  state  fully  and  clearly 
the  fundamental  principles  of  the  construction  and  maintenance  of 
roads  and  pavements. 

In  the  preparation  of  the  book  the  endeavor  has  been  to  ob- 
serve a  logical  order  and  a  due  proportion  between  the  different 
parts;  and  great  care  has  been  taken  in  classifying  and  arranging 
the  matter.  It  will  be  helpful  to  the  reader  to  notice  that  the  vol- 
ume is  divided  successively  into  parts,  chapters,  articles,  sections 
having  small-capital  black-face  side-heads,  sections  having  lower- 
case black-face  side-heads,  sections  having  lower-case  italic  side- 
heads,  and  sections  having  simply  the  serial  number.  In  some 
cases  the  major  subdivisions  of  the  sections  are  indicated  by  small 
numerals.  The  constant  aim  has  been  to  present  the  subject 
clearly  and  concisely. 

Every  precaution  has  been  taken  to  present  the  work  in  a  form 
for  convenient  practical  use  and  ready  reference.  Numerous  cross 
references  are  given  by  section  number;  and  whenever  a  table  or  a 
figure  is  mentioned,  the  citation  is  accompanied  by  the  number  of 
the  page  on  which  it  may  be  found.  The  table  of  contents  shows 
the  general  scope  of  the  book;  the  running  title  assists  in  finding 
the  different  parts;  and  a  very  full  index  makes  everything  in  the 
book  easy  of  access. 

The  author  will  esteem  it  a  favor  if  any  errors  that  may  be 
found  are  at  once  brought  to  his  notice. 

L  O.  B 

Champaign,  III., 

November  27,  1902. 


TABLE  OF  CONTENTS. 


PAGE 

Introduction 1 

PART  I.    COUNTRY  ROADS. 
CHAPTER  I.    ROAD  ECONOMICS. 

Advantages  of  Good  Roads.  Cost  of  Wagon  Transportation. 
Financial  Value  of  Good  Roads.  Tractive  Resistance  Power  of  a 
Horse.  Road  Administration.  Road  Taxes.  Expenditures  for  Roads. 
State  Aid 3 

CHAPTER  II.     ROAD  LOCATION. 

Elements  Involved.  Distance.  Grade.  Rise  and  Fall.  Curves. 
Width.  Cross  Section.  Placing  the  Line.  Establishing  the  Grade 
Line 45 

CHAPTER   III.     EARTH  ROADS. 

Art.  1.  Construction.     Drainage.     Width    of    Wheelway.     Cross 
Section.     Excavation  and  Embankment.     Improving  Old  Roads.     Road- 
building  Machinery.     Scrapers.     Scraping  Grader.     Elevating  Grader. 
Cost    of    Earthwork.     Bridges.     Waterways.     Culverts.     Guard    Rails. 
Guide  Posts.     Artistic  Treatment 71 

Art.  2.  Maintenance.     Destructive  Agents.     Care   of   the  Surface. 
Care  of  Side  Ditches.     Care  of  Roadside.     Obstruction  by  Snow.     Pre- 
vention of  Dust.     Cost  of  Road  Maintenance.     Road  Administration. 
Maintenance  by  Contract 125 

Art.  3.  Sand  Roads.  Drainage.  Grading.  Shade.  Hardening 
the  Surface ; 144 

CHAPTER  IV.  GRAVEL  ROADS. 

Art.   1.  The  Gravel.     Requisites  for  Road  Gravel.     Distribution 

of  Gravel.     Characteristics  of  Different  Gravels 146 

Art.  2.  Construction.     Drainage.     Crown.     Forms   of    Construc- 

v 


Vi  TABLE   OF   CONTENTS. 


PAGE 

tion.     Bottom   Course.     Screening   the   Gravel.     Hauling   the   Gravel. 
Measuring  the  Gravel.     Economic  Value  of  a  Gravel  Surface.     Gravel 

vs.  Broken-stone  Roads 162 

Art.  3.  Maintenance.  Destructive  Agents.  Work  of  Mainte- 
nance.    Repairs.     Sprinkling.     Cost 174 

CHAPTER  V.      BROKEN-STONE  ROADS. 

Art.  1.  The  Stone.  Requisites  for  Road  Stone.  Method  of  Test- 
ing Stone.       Characteristics  and  Distribution  of  Road-building  Rocks. .    177 

Art.  2.  Construction.  Forms  of  Construction.  Earth  Shoulders. 
Crown.  Thickness.  Examples  of  Cross  Sections.  Permissible  Grades. 
Preparing  the  Subgrade.  Setting  the  Telford.  Crushing  the  Stone. 
Sizes  of  Stone.  Spreading  the  Stone.  Shrinkage  in  Rolling.  Rollers. 
Rolling  the  Stone.     Binding  the  Road.     Cost  of  Construction 195 

Art.  3.  Maintenance.  Agents  of  Destruction.  Amount  of  Wear. 
Methods  of  Maintenance.  Work  of  Maintenance.  Economics  of  the 
Stone  Road 241 

CHAPTER  VI.      MISCELLANEOUS  ROADS. 

Wheelways.  Burned-clay  Roads.  Concrete  Roads.  Shell  Roads. 
Slag  Roads  Coal-slack  Roads.  Plank  Roads.  Corduroy  Roads 
Charcoal  Roads 263 

CHAPTER  VII.     EQUESTRIAN  ROADS  AND  HORSE-RACE  TRACKS. 

Art.  1.  Equestrian  Roads.  Width  and  Crown.  Drainage.  Sur- 
face   276 

Art.  2.  Horse-race  Tracks  Form:  oval,  kite,  easement  curves. 
Super-elevation.     Grades.     Surface.     Drainage 278 


PART  II.     STREET   PAVEMENTS. 

Importance  of  Pavements 293 

CHAPTER  VIII       PAVEMENT  ECONOMICS. 

Benefits  of  Pavements.  Apportionment  of  Cost  Special  Assess- 
ments Guaranteeing  Pavements.  Maintenance  by  Contract.  Tear- 
ing up  Pavements 295 

CHAPTER   IX.      STREET   DESIGN. 

Street  Plan:  checkerboard,  diagonal,  concentric,  size  of  lots  and 
blocks.  Width  of  Streets  Area  of  Streets.  Width  of  Pavement. 
Street  Grades.  Crown  of  Pavement.  Cross  Section  of  Side-hill  Streets 
Plans  and  Specifications.     Street  Trees 307 


TABLE    OF  CONTENTS.  Vll 


CHAPTER  X.      STREET   DRAINAGE. 

PAGE 

Subdrainage.  Catch  Basins.  Gutters.  Drainage  at  Street  Inter- 
section.    Surface  Drainage.     Crown 335 

CHAPTER  XI.   CURBS  AND  GUTTERS. 

Curb:  stone,  concrete.  Gutters.  Combined  Concrete  Curb  and 
Gutter.     Other  Forms  of  Curb.     Radius  of  Curb  at  Street  Corner 350 

CHAPTER  XII.   PAVEMENT  FOUNDATIONS. 

Art.  1.  Preparation  of  the  Subgrade.  Drainage.  Earthwork. 
Rolling  the  Subgrade.     Filling  Trenches 360 

Art.  2.  Concrete  Foundation.  Advantages  of  Concrete  Foun- 
dation. Theory  of  Concrete.  Tables  of  Quantities  for  a  Yard.  Mix- 
ing the  Concrete.     Laying  the  Concrete.     Cost  of  Concrete 367 

Art.  3.  Miscellaneous  Foundations.  Macadam.  Bituminous 
Concrete.     Gravel.     Sand.     Plank 382 

CHAPTER  XIII.      ASPHALT  PAVEMENTS. 

Art.  1.    The  Asphalt.      Nomenclature.      General   Characteristics. 

Chemical  Composition.     Physical  Properties.     Location  of  Mines 383 

Art.  2.  Sheet-Asphalt  Pavements.  Historical.  The  Founda- 
tion. Binder  Course.  Cushion  Coat.  Asphaltic  Cement.  The  Sand. 
The  Wearing  Coat.  Causes  of  Failures.  Method  of  Repairing.  Cost  of 
Sheet-Asphalt  Pavements.  Cross  Section  of  Asphalt  Pavement.  Max- 
imum Grades      Merits  and  Defects 397 

Art.  3.  Rock- Asphalt  Pavements.     Method  of  Construction 446 

Art.  4.  Asphalt -Block  Pavement.      The  Blocks.      Specifications 

for  Laying.     Merits  and  Defects.     Cost.     Durability 447 

Art.  5.  Asphalt  Macadam.     Warren's  Method.     Whinery's  Method.  452 
Art.  6.  Coal-tar   Roads   and   Pavements.     Coal-tar  Pavements. 
Cost.     Tar  Macadam 454 

CHAPTER  XIV.      BRICK  PAVEMENTS. 

Art.  1.  The  Brick.  The  Clay.  Manufacture  of  the  Brick.  Re- 
quisites for  Paving  Brick.  Testing  the  Brick:  appearance;  color;  trans- 
verse strength;  absorption;  abrasion — Orton's  method,  N.  B.  M.  A. 
standard,  Talbot-Jones  method 462 

Art.  2.  Construction  Foundation.  Cushion  Layer.  Laying 
the  Brick.  Rumbling.  Permissible  Grades.  Merits  of  Brick  Pave- 
ments.    Cost 494 

Art.  3.  Maintenance.     Guarantee 522 

CHAPTER  XV.      COBBLE-STONE  PAVEMENT. 

Grading.  The  Stones.  Setting  the  Stones.  Cost.  Merits  and 
Defects 525 


Vlll  TABLE    OF    CONTENTS. 


CHAPTER  XVI.      STONE-BLOCK  PAVEMENT. 

PAGE 

Nomenclature 528- 

Art.  1.  The  Stone.     Granite.     Trap.     Sandstone.     Limestones 531 

Art.  2.  Construction.     Foundation.     Sand  Cushion.     The  Blocks. 

Setting  the  Blocks.     Ramming.     Maximum  Grade.     Merits  and  Defects . 

Cost 536 

CHAPTER  XVII.      WOOD-BLOCK  PAVEMENTS. 

Art.  1.  The  Wood.  Varieties.  Quality  of  Wood.  Preservation 
of  Wood 549 

Art.  2.  The  Construction.  Round-block  Pavement:  foundation, 
the  blocks,  laying  the  blocks,  cost.  Rectangular-block  Pavement: 
foundation,  the  blocks,  placing  the  block,  filling  the  joints,  expansion, 
repairs,  permissible  grades,  merits  and  defects,  cost 553 

CHAPTER    XVIII.      COMPARISON    OF    PAVEMENTS. 

Definitions.  Relative  Amounts  of  Different  Kinds  of  Pavements  in 
United   States 563- 

Requirements  of  an  Ideal  Pavement.  Cost,  Durability: 
traffic  census,  modifying  elements,  comparison  of  economic  features  of 
block  and  continuous  pavements.  Tractive  Resistance.  Slipperiness. 
Ease  of  Cleaning.  Noiselessness.  Healthfulness.  Freedom  from  Dust 
and  Mud.     Comfort  in  Use.     Temperature 566 

Selecting  the  Best  Pavement.  Importance  of:  first  cost,  annual 
cost,  ease  of  traction,  foothold,  ease  of  cleaning,  noiselessness,  health- 
fulness,  freedom  from  dust  and  mud,  smoothness 581 

CHAPTER    XIX.      SIDEWALKS. 

Location.  Width.  Transverse  Slope.  Grade.  Asphalt  Walk: 
sheet,  block.  Brick  Walks :  foundation,  the  brick,  direction  of  courses, 
laying,  brick  crossings,  cost.  Cement  Walks:  foundation,  forms,  con- 
crete base,  wearing  coat,  joints,  expansion,  color,  slipperiness,  cost. 
Cinder  Walks.  Gravel  Walks.  Macadam  Walks.  Plank  Walks. 
Stone  Walks :  crossings,  cost 590 

CHAPTER  XX.      BICYCLE  PATHS  AND  RACE  TRACKS. 

Art.  1.  Bicycle  Paths.  City  Bicycle  Paths:  location,  width, 
materials,  grade,  cross  section,  examples,  cost,  Country  Bicycle  Paths: 
location,  width,  grade,  cross  section,  construction,  maintenance 624 

Art.  2.  Bicycle-race  Tracks.  Ground  Plan:  present  practice, 
ideal  form.     Super-elevation.     Construction 632 


ROADS  AND  PAVEMENTS. 


INTRODUCTION. 

The  problems  involved  in  the  construction  and  maintenance 
of  rural  highways  differ  materially  from  those  which  are  encountered 
in  the  improvement  and  care  of  city  streets,  and  therefore  this  dis- 
cussion of  the  subject  of  Roads  and  Pavements  will  be  divided  into 
Part  I,  Country  Roads,  and  Part  II,  City  Pavements.  In  each 
division  of  the  subject  certain  general  principles  will  first  be  con- 
sidered, and  the  further  discussion  will  be  divided  according  to 
the  several  materials  in  use  for  the  road  surface.  It  will  not  always 
be  possible  to  keep  the  several  portions  entirely  distinct,  but  a 
knowledge  of  the  intention  in  this  respect  will  make  it  easier  to 
understand  the  method  of  presentation  or  to  turn  readily  to  the 
discussion  of  any  particular  phase  of  the  subject. 

1 


PART    I. 

COUNTEY   EOADS. 

Part  I  will  include  matters  relating  to  earth,  gravel,  and  broken- 
stone  roads  in  rural  districts,  although  some  of  the  discussion  is 
also  applicable  to  these  road  surfaces  when  employed  in  city  streets. 


CHAPTER  I. 

ROAD   ECONOMICS. 

1.  ADVANTAGES  OF  GOOD  ROADS.  Good  roads  are  so  im- 
portant in  the  financial,  social  and  educational  well-being  of  a  rural 
community  that  no  enumeration  of  their  advantages  is  likely  to 
include  all  the  benefits;  but  a  brief  consideration  of  some  of  the 
chief  advantages  of  good  roads  will  be  of  value  in  determining  the 
amount  of  money  that  may  justifiably  be  expended  to  secure  road 
improvement  and  in  deciding  what  classes  should  in  equity  bear 
this  expense.  The  principal  advantages  of  good  roads,  i.  e.,  of 
permanently  hard  ones,  are  as  follows: 

1.  Good  roads  decrease  the  cost  of  transportation, — at  some 
seasons  of  the  year  considerably,  but  at  others  only  a  little.  This 
item  will  be  considered  more  fully  later  (see  §  4-9). 

2.  Good  roads  permit  the  cultivation  of  crops  not  otherwise 
marketable.  This  advantage  results  in  extending  the  area  devoted 
to  the  cultivation  of  fruits  and  vegetables,  and  is  most  effective  in 
the  vicinity  of  a  large  city. 

3.  Good  roads  give  a  wider  choice  of  time  for  the  marketing  of 
crops.     In  some  instances  good  roads  permit  the  crops  to  be  mar- 

3 


EOAD    ECONOMICS.  [CHAP.   I, 


keted  when  the  labor  of  production  is  less  pressing:  but  this  advan- 
tage accrues  only  to  the  producers  of  imperishable  crops,  and  is  not 
of  great  importance,  since  the  labor  required  to  market  the  product 
is  small  in  comparison  with  that  of  production. 

4.  Good  roads  permit  the  marketing  to  be  done  when  the  prices 
are  most  favorable.  This  advantage  is  more  important'  with  per- 
ishable than  with  imperishable  products.  As  far  as  perishable 
products  are  concerned,  this  advantage  is  virtually  included  in 
paragraph  2  above.  As  far  as  imperishable  products  are  concerned, 
this  advantage  is  important  only  near  a  large  city,  i.  e.,  where  the 
producer  sells  directly  to  the  consumer.  Prices  of  staple  farm 
products  (not  garden  products)  are  not  much  affected  by  roads, 
since  the  condition  of  the  roads  is  local  while  prices  are  governed 
by  world-wide  conditions.  Writers  on  good-road  economics  usually 
greatly  overestimate  this  advantage  as  far  as  the  ordinary  producer 
of  imperishable  products  is  concerned.  If  this  advantage  were 
anything  like  as  great  as  is  frequently  claimed,  producers  would 
store  such  products  at  the  local  shipping  point,  or  in  the  great  city, 
or  at  the  port  of  export,  awaiting  a  favorable  price.  Such  storage 
would  also  permit  the  delivery  at  a  time  when  other  work  was  least 
pressing.  The  expense  of  storage  at  the  local  shipping  point  is  a 
small  per  cent  of  the  value  of  the  product.  It  is  frequently,  but 
erroneously,  claimed  that  hard  roads  would  save  the  Illinois  farmer 
3  to  5  cents  per  bushel — an  amount  10  to  15  times  the  cost  of  the 
storage.  Since  producers  do  not  so  store  their  products,  it  is  safe 
to  assume  that  this  advantage  of  good  roads  as  a  rule  is  not  very 
great.  The  present  method  of  doing  business  makes  this  advantage 
comparatively  unimportant. 

5.  Good  roads  give  a  wider  choice  of  the  market  place.  This 
advantage  affects  perishable  products  chiefly,  and  for  geographical 
reasons  is,  as  a  rule,  not  very  great. 

6.  Good  roads  tend  to  equalize  the  produce  market  between 
different  climatic  conditions.  In  the  absence  of  railroad  trans- 
portation and  cold  storage,  this  advantage  might  be  of  considerable 
local  importance;  but  under  ordinary  conditions  it  is  compara- 
tively unimportant. 

7.  Good  roads  tend  to  equalize  railroad  traffic  Between  the 
different  seasons  of  the  year.     Impassable  wagon  roads  over  any 


ADVANTAGES    OF    GOOD    ROADS. 


considerable  area  materially  decrease  the  amount  of  agricultural 
products  to  be  transported  by  railroads,  and  a  return  of  good  roads 
will  for  a  time  congest  the  railroad  transportation  facilities.  The 
effect  of  good  roads  in  equalizing  railroad  transportation  is  partially 
neutralized  by  the  fact  that  agricultural  products  are  only  one  of 
many  classes  of  commodities  transported  by  the  railroads ;  and  also 
by  the  fact  that  most  railroads  transport  agricultural  products  origi- 
nating over  a  considerable  area,  and  bad  wagon  roads  are  not  likely 
to  occur  all  over  the  contributory  area  at  the  same  time;  and 
further  by  the  fact  that  the  storage  capacity  of  warehouses  helps 
to  equalize  the  traffic. 

8.  Good  roads  tend  to  equalize  mercantile  business  between 
different  seasons  of  the  year.  Merchants  having  a  considerable  rural 
custom  could  do  business  more  economically  if  the  trade  were  dis- 
tributed uniformly  throughout  the  year.  However,  the  succession 
of  good  and  bad  wagon  roads  is  only  one  cause  of  the  unequal  dis- 
tribution of  rural  patronage. 

9.  Good  roads  permit  more  easy  intercourse  between  the  mem- 
bers of  rural  communities,  and  also  between  rural  and  urban  popu- 
lations. This  is  an  important  benefit,  particularly  in  a  republican 
form  of  government. 

10.  Good  roads  facilitate  the  consolidation  of  rural  schools,  and 
thereby  increase  their  economy  and  efficiency.  This  is  an  impor- 
tant matter  to  coming  generations. 

11.  Good  roads  facilitate  rural  mail  delivery,  and  thereby  tend 
to  improve  the  social  and  intellectual  condition  of  the  rural  popu- 
lation. 

12.  Good  roads  sometimes  change  rural  into  suburban  property, 
and  sometimes  are  a  material  factor  in  inducing  tourist  travel  and 
securing  vacation  residents. 

2.  It  is  customary  to  include  the  increase  in  the  price  of  farming 
land  as  one  of  the  benefits  of  good  roads;  but  the  increase  in  price 
of  land  is  simply  the  measure  of  the  value  of  all  the  above  advan- 
tages, and  hence  should  not  be  included. 

3.  Notice  that  the  first  eight  advantages  mentioned  above  relate 
to  the  financial  benefits  of  hard  roads,  and  the  last  four  to  the  social 
benefits.  In  the  past  writers  upon  good-road  economics  have  given 
much  attention  to  the  supposed  financial  benefit  of  hard  roads  and 


ROAD    ECONOMICS.  [CHAP.I. 


little  or  none  to  the  social  advantage.  Any  considerable  expendi- 
ture for  the  improvement  of  rural  highways  can  not  be  justified  on 
financial  grounds  alone  (see  §  9).  Good  roads  are  chiefly  desirable 
for  the  same  reason  that  a  man  buys  a  carriage  or  builds  a  fine 
house,  i.  e.,  because  they  are  a  comfort  and  a  pleasure.  Good  roads 
are  to  be  urged  principally  for  the  same  reason  that  good  schools 
are  maintained,  namely,  because  they  increase  the  intelligence  and 
value  of  the  citizen  to  society. 

4.  Cost  of  Wagon  Transportation.    The  chief  financial 
advantage  of  hard  roads  is  the  decreased  cost  of  transportation 
It  is  proposed  to  inquire  briefly  concerning  the  cost  of  wagon 
transportation  with  a  view  of  determining  the  proportion  of  this 
cost  that  may  be  saved  by  road  improvement. 

In  this  connection,  a  distinction  must  be  made  between  the  cost 
to  those  whose  chief  business  is  to  sell  transportation,  and  the  cost 
to  those  to  whom  transportation  is  a  mere  incident  of  a  business 
organized  for  some  other  purpose.  The  first  class  is  represented 
by  a  freighter,  or  a  transportation  company,  and  the  second  by  a 
farmer  or  producer.  The  former  maintains  his  teams  and  wagons 
only  to  transport  freight,  while  ordinarily  the  latter  keeps  his  teams 
and  wagons  primarily  for  general  farm  work  of  which  transporta- 
tion on  the  roads  is  only  a  small  part.  In  some  cases  the  traffic 
to  be  considered  is  principally  that  by  freighters,  but  usually  the 
chief  traffic  over  country  roads  is  that  connected  with  agricultural 
operations. 

Again,  consideration  should  be  given  only  to  hauling  in  which 
the  load  is  equal  to  the  full  capacity  of  the  team  for  the  particular 
condition  of  the  roads.  A  farmer  may  employ  a  two-horse  team 
to  take  a  bushel  of  potatoes  to  town,  or  a  grocery  wagon  may  make 
a  trip  to  deliver  a  pound  of  cheese;  but  the  partial  load  is  entirely 
independent  of  the  condition  of  the  roads. 

Further,  it  is  necessary  to  notice  that  only  the  rate  for  full  loads 
should  be  considered.  If  a  number  of  packages  are  carried  in  the 
same  load  for  different  parties,  part  of  the  charge  is  to  cover  the  cost 
of  collection,  distribution,  possible  partial  loads,  etc.;  and  there- 
fore only  part  of  the  charge  is  for  transportation  proper. 

5.  Cost  to  Freighters.  The  cost  will  vary  greatly  with  the 
conditions  of  the  service,  i.  e.,  with  the  character   of  the  road 


COST   OF   WAGON    TRANSPORTATION. 


surface,  the  average  grade  of  the  road,  the  maximum  grade,  return 
load,  etc. 

Except  in  rare  cases,  the  cost  per  ton-mile  for  loads  one  way 
upon  earth  roads  will  not  be  more  than  25  cents,  and  ordinarily  it 
will  not  be  more  than  15  to  20  cents;  *  while  with  easy  grades  and 
favorable  road  surface  it  may  be  as  low  as  10  to  15  cents,  and  with 
long  hauls,  return  loads,  and  favorable  road  surface,  it  may  be  8  to 
10  cents.  When  the  last  price  is  obtained  there  is  little  need  or 
opportunity  for  road  improvement. 

6.  Cost  to  Farmers.  In  this  division  of  the  subject,  a  distinc- 
tion should  be  made  between  producers  of  perishable  products  and 
producers  of  non-perishable  products.  The  first  class  is  represented 
by  gardeners,  dairymen,  fruit-growers,  etc.;  and  the  second,  by 
producers  of  hay,  grain,  cotton,  etc. 

The  cost  of  transportation  is  much  greater  for  perishable  than 
^r  non-perishable  products.  In  the  first  place,  the  marketing  of 
perishable  products  is  an  important  factor  in  comparison  with 
the  cost  of  production,  and  frequently  necessitates  an  independent 
transportation  department;  while  the  labor  of  marketing  non- 
perishable  products  is  comparatively  small — particularly  as  in 
most  localities  where  there  is  much  of  this  class  of  produce,  the  dis- 
tance from  the  farm  to  the  railroad  station  is  short.  Further, 
perishable  products  must  go  to  market  whatever  the  condition  of 
the  roads,  while  non-perishable  ones  can  wait  for  comparatively 
favorable  conditions;  and  finally,  the  former  frequently  go  to 
market  in  partial  loads,  and  the  second  usually  in  full  loads.  Ex- 
cept in  comparatively  limited  districts,  non-perishable  products 
make  up  the  bulk  of  the  traffic  on  the  country  roads.  According 
to  the  U.  S.  Census  of  1890,  the  gardeners,  fruit-growers,  dairymen, 
vine-growers,  florists,  and  nurserymen  constitute  only  1.8  per  cent 
of  the  so-called  farming  class. 

7.  The  cost  of  transporting  perishable  products  is  probably 
greater  than  that  for  any  other  class  of  traffic  over  the  country 
roads;  but  as  it  is  next  to  impossible  to  secure  any  reliable  data 
no  attempt  will  be  made  to  present  any  general  conclusions.     For 

*See  "  Cost  of  Wagon  Transportation,"  by  the  author,  in  Proceedings  of  Illinois 
Society  of  Engineers,  Vol.  16,  p.  36-44;  full  abstract  of  the  same  in  Engineering 
News,  Vol.  45,  p.  86. 


ROAD    ECONOMICS.  [CHAP.   I. 


several  reasons,  this  traffic  will  usually  justify  larger  expense  for 
road  improvement  than  any  other. 

The  cost  of  transportation  to  farmers  proper,  i.  e.,  producers  of 
non-perishable  products,  depends  chiefly  upon  the  condition  of 
the  road  surface  and  upon  the  demands  of  general  farm  work. 
Loam  or  clay  roads  are  reasonably  good  when  dry,  and  are  therefore 
at  least  passable  most  of  the  year;  while  sand  roads  are  at  their 
worst  when  dry,  and  are  therefore  in  their  worst  condition  during 
the  greater  part  of  the  year.  Fortunately  sand  roads  are  less  com- 
mon, the  country  over,  than  clay  or  loam  roads.  In  the  crop 
season,  with  a  little  choice  as  to  the  time  of  doing  the  work  the  cost 
on  fairly  level  loam  or  clay  roads  is  probably  not  more  than  10  to 
12  cents  per  ton-mile;  and  when  farm  work  is  not  pressing,  the  cost 
is  not  more  than  8  to  10  cents  per  ton-mile.* 

8.  A  Conflicting  View.  In  current  literature  on  road  economics, 
the  claim  is  frequently  made  that  the  cost  of  wagon  transportation 
to  the  farmer  is  considerably  more  than  stated  in  §  6.  Apparently 
most  of  these  claims  are  based,  either  directly  or  indirectly,  upon 
data  published  in  Circular  19  of  the  Road  Inquiry  Office  of  the 
United  States  Department  of  Agriculture.  As  the  general  relia- 
bility of  the  data  in  that  circular  is  discussed  in  §  13-19,  and  the 
part  referring  to  cost  of  wagon  transportation  is  considered  in 
§  20-24,  the  matter  will  not  be  discussed  here. 

9.  FINANCIAL  VALUE  OF  ROAD  IMPROVEMENT.  It  is  not 
possible  to  present  any  valuable  general  conclusions  as  to  the 
saving  in  cost  of  transportation  attainable  by  any  proposed  road 
improvement. 

For  any  particular  road  where  the  traffic  is  principally  by 
"  freighters "  as  defined  in  §  5;  it  is  possible  to  arrive  at  a  rough 
approximation  by  (1)  taking  a  census  of  the  traffic,  (2)  making  an 
estimate  of  the  present  cost  per  ton-mile,  and  (3)  making  an  esti- 
mate of  the  cost  after  the  improvement.  The  amount  of  traffic 
varies  with  the  condition  of  the  road  surface,  and  the  chief  difficulty 
is  to  determine  the  advantage  of  being  able  to  move  freight  at  any 


*  See  "Cost  of  Wagon  Transportation," by  the  author,  in  Proceedings  of  Illinois 
Society  of  Engineers,  Vol.  16,  p.  36-M;  full  abstract  of  the  same  in  Engineering 
Feios,  Vol.  45,  p.  86. 


ESTIMATED    COST    OF    BAD    ROADS. 


time.  This  advantage  will  depend  upon  the  proportion  of  the  time 
that  the  roads  are  "good,"  which  depends  entirely  upon  the  locality 
and  the  nature  of  the  road  surface,  and  varies  greatly  from  year  to 
year.  Ordinarily  the  road  is  used  by  a  variety  of  teamsters,  and 
the  cost  varies  with  the  particular  circumstances  of  each.  There 
will  rarely  be  conditions  to  which  this  method  of  investigation  can 
be  applied  with  any  degree  of  certainty.  At  best  the  results  of 
such  an  investigation  must  be  regarded  as  mere  approximations, 
since  no  factor  of  the  problem  can  be  determined  accurately,  and 
since  any  slight  error  in  the  estimated  saving  per  ton-mile  is  greatly 
magnified  when  multiplied  by  the  number  of  ton-miles.  Never- 
theless such  an  investigation  is  desirable  to  aid  the  judgment,  but 
its  approximate  nature  should  not  be  forgotten. 

For  roads  where  the  traffic  is  by  farmers  the  difficulties  are  still 
greater.  The  number  of  users  is  greater,  the  cost  of  transportation 
to  the  different  users  varies  very  greatly,  and  the  value  of  being  able 
to  use  the  road  at  any  time  is  very  different  with  different,  users, 
and  for  the  same  class  of  users  varies  with  the  locality  and  the 
nature  of  the  road. 

The  amount  of  money  that  may  justifiably  be  expended  for  any 
proposed  road  improvement  will  depend  upon  the  present  condition 
of  the  road,  the  amount  and  the  nature  of  the  traffic,  and  the  cost  of 
constructing  and  maintaining  the  improved  road.  The  question  is 
a  local  one,  and  can  be  answered  approximately  correctly  only 
after  careful  study  of  the  conditions.  Ordinarily  the  saving  in 
transportation,  except  near  large  cities,  will  not  justify  any  radical 
road  improvement;  but  with  a  miscellaneous  traffic,  the  social 
advantages  of  road  improvement  should  be  taken  into  consideration, 
even  though  they  can  not  be  computed  in  dollars  and  cents. 

10.  ESTIMATED  COST  OF  BAD  ROADS.  Most  of  the  current 
literature  on  good-road  economics  greatly  exaggerates  the  financial 
advantage  of  road  improvement.  Three  such  estimates  will  be 
examined. 

11.  A  Wild  Guess.  A  favorite  method  of  showing  the  waste- 
fulness of  bad  roads  is  to  compare  the  efficiency  of  horses  on  Euro- 
pean and  American  roads.  Some  claim  that  a  horse  in  Europe 
does  twice  as  much  work  as  in  America,  solely  because  of  the  better 
roads;  while  others  claim  that  three  horses  in  Europe  do  as  much 


10  ROAD   ECONOMICS.  [CHAP.  I. 

as  four  in  America.  The  annual  cost  of  bad  roads  to  the  American 
farmer  is  then  said  to  be  the  annual  cost  of  feeding  one  quarter  to 
one  half  of  all  the  horses  in  America  plus  the  annual  interest  on  the 
value  of  the  superfluous  horses.     The  results  are  truly  appalling. 

In  the  first  place,  the  premise  is  a  mere  guess,  since  it  is  impos- 
sible off-hand  to  state  the  relative  efficiency  of  horses  in  Europe  and 
in  America. 

In  the  second  place,  the  above  line  of  argument  assumes  that 
all  horses  are  continuously  upon  the  road.  This  assumption  is 
seriously  in  error,  since  there  are  a  large  number  of  horses  in  the 
cities  not  in  any  way  connected  with  the  farms,  and  further  since 
the  horses  on  the  farms  include  a  number  too  young  to  work,  and 
still  further  since  most  farmers  require  considerably  more  horses  to 
raise  the  crops  than  to  transport  them  to  market. 

12.  A  Rough  Estimate,  Another  common  method  of  demon- 
strating the  cost  of  bad  roads  is  to  estimate  the  saving  per  horse 
due  to  improved  roads.  The  annual  saving  per  horse  is  variously 
estimated  at  from  $10  to  $20,  and  the  saving  in  vehicles  and  harness 
is  estimated  as  equivalent  to  $5  per  horse,  making  a  total  annual 
saving  by  good  roads  of  $15  to  $25  per  horse.  This  sum  is  then 
multiplied  by  the  number  of  horses  given  in  the  census  report  or 
returned  by  the  tax  assessor,  and  the  product  is  said  to  be  the  annual 
loss  by  the  farmers  due  to  bad  roads.     The  result  is  startling. 

No  evidence  is  offered  to  show  the  actual  loss  by  bad  roads. 
Possibly  a  horse  continually  on  the  road  could  earn  $10  to  $20  per 
year  more  on  good  roads  than  on  poor  ones.  But,  on  the  contrary, 
farmers  claim  that  the  damage  to  a  horse  through  continuously 
driving  on  "good  roads,"  i.  e.,  on  stone  roads,  is  more  than  $20  per 
annum.  "The  hard  roads  stiffen  up  a  horse."  The  cost  of  keeping 
a  horse  shod  is  considerably  more  with  stone  than  with  earth  roads. 
These  losses  due  to  permanently  hard  roads  are  reasonably  certain, 
while  the  advantages  claimed  are  problematic.  Possibly  the  dam- 
age to  harness  is  more  with  poor  than  with  good  roads;  but 
farmers  claim  that  vehicles  wear  out  faster  on  stone  than  on  earth 
roads.  In  short,  the  advantages  are  not  all  on  one  side,  and  the 
saving  claimed  is  not  proved. 

Even  though  a  horse  continually  on  the  road  could  and  would 
earn  $15  per  annum  more  on  good  roads  than  on  poor  ones,  the 


ESTIMATED    COST    OF    BAD    ROADS. 


11 


above  estimate  is  grossly  in  error,  since  only  a  small  per  cent  of  the 
horses  are  on  the  road  all  the  time,  or  since  the  average  horse  is  on 
the  road  only  a  very  small  part  of  the  time.  Unquestionably  a 
horse  can  do  more  work  on  good  roads  than  on  poor  ones,  but  that 
does  not  prove  that  farmers,  gardeners,  etc.,  as  a  rule,  would  re- 
quire fewer  horses  with  better  roads  or  that  their  horses  would  earn 
more. 

13.  Statistical  Results.  Circular  No.  19,  published  under  date 
of  April  4,  1896,  by  the  Road  Inquiry  Office  of  the  United  States 
Department  of  Agriculture,  contains  data  as  to  the  cost  of  bad 
roads  and  the  saving  possible  through  road  improvement.  The 
conclusions  of  this  circular  have  been  so  widely  quoted  and  so 
generally  accepted  as  to  justify  a  careful  consideration  of  them 
here.*    Table  1  is  from  that  circular. 


TABLE  1. 
Data  on  Cost  of  Wagon  Transportation. 


Ref. 

No. 

Locality. 

Average 

Distance 

Hauled, 

Miles. 

Average 
Load 

Hauled, 
Tons. 

Average 

Cost  per 

Ton-mile, 

Cents. 

Total  Cost 

from  Farm 

to  Market, 

per  Ton. 

1 

Eastern  States  . ,              .... 

5.9 
6.9 
8.8 

12.6 
8.8 

23.3 

1.108 

32 
27 
31 
25 
22 
22 

$1   89 

9, 

Northern  States 

1   86 

3 

Middle-Southern  States 

Cotton  States 

Prairie  States 

Pacific  Coast  and  Mountain 

Whole  United  States 

2  72 

4 
5 
6 

0.688 
1.204 
1.098 

3.05 
1.94 
5.12 

7 

12.1 

1.001 

25 

3.02 

The  author  inquired  of  the  Road  Inquiry  Office  as  to  various 
details  of  the  investigation,  and  in  reply  received  the  data  in  Table 
2,  page  12,  with  a  statement  that  it  contained  all  that  was  then 
known  about  the  statistics. 

14.  Elaborateness  of  the  Investigation.  Owing  to  its  seeming 
elaborateness,  the  above  official  investigation  has  carried  great 
weight.  The  statement  that  ten  thousand  letters  were  sent  out, 
apparently  creates  the  conviction  that  the  investigation  was  *a 
very  elaborate  one ;  but  the  area  to  be  covered  was  very  great,  and 

*  For  data  from  a  later  investigation,  see  Supplemental  Note,  page  44a. 


12 


KOAD   ECONOMICS. 


[CHAP.  I. 


TABLE  2. 
Data  on  Cost  of  Wagon  Transportation  by  States. 


State. 


Number  of 

Counties 
Answering. 


Average 
Haul, 
Miles. 


Average 

Load, 
Pounds. 


Cost  per 
Ton-mile. 


Alabama 

Arizona 

Arkansas 

California 

Colorado 

Connecticut  , .  . 

Florida 

Georgia 

Idaho 

Illinois    

Indiana 

Iowa 

Kansas 

Kentucky 

Louisiana 

Maine 

Maryland  ..... 
Massachusetts  . 

Michigan 

Minnesota 

Mississippi 

Missouri 

Montana 

Nebraska 

New  Hampshire 
New  Jersey  .... 
New  Mexico. . . . 

New  York 

North  Carolina.. 
North  Dakota  . 

Ohio 

Oregon 

Pennsylvania..  . 
South  Carolina  . 
South  Dakota. . 

Tennessee 

Texas 

Utah 

Vermont 

Virginia 

Washington  .  .  . 
West  Virginia . . 

Wisconsin 

Wyoming 

United  States  . . 


23 

1 
31 
20 
23 

3 
25 
63 

8 
56 
42 
44 
52 
54 
23 

5 
12 

4 
26 
33 
35 
49 
15 
39 

5 

8 

7 
30 
43 
22 
43 
14 
25 
11 
23 
45 
74 
14 

5 
42 
18 
18 
25 

3 


12.77 

60.00 

24.30 

10.9 

10.5 
6.6 
7.5 
8.8 

24.5 
5.5 
4.6 
5.4 
9.3 
8. 

13. 
8.8 
4.5 
6.7 
7. 
8.5 

14.3 
9. 

14.5 
9.4 
4.6 
4. 

34. 
6. 

11.5 

13. 
5. 

10. 
6.6 
6.3 

11.8 

10.4 

18. 

38. 
5. 
9. 


7. 
12. 

7. 
40. 


1061 


12.1 


1383 
2  000 

1  419 

2  480 
2  417 
2  000 
1246 
1382 
2  325 
2  250 
2  272 
2  071 
2  420 
1995 
1443 
2  050 
1991 
2  750 
1874 
2  226 
1268 
1773 
2  400 
2  190 
2  400 
2  100 
1584 
2  220 
1360 
2  986 
2  193 
2  000 
2  036 
1409 
2  330 
1540 
1523 
2  221 
2  200 
1719 
2  350 
1886 
2  184 
2  800 


$  0.25 
.25 
.21 
.22 
.20 
.34 
.39 
.24 
.22 
.23 
.28 
.24 
.17 
.35 
.25 
.24 
.29 
.33 
.27 
.21 
.25 
.22 
.23 
.21 
.31 
.38 
.20 
.26 
.24 
.18 
.28 
.33 
.34 
.25 
.23 
.25 
.17 
.14 
.31 
.29 
.21 
.40 
.26 
.11 


2  002 


$  0.25 


ESTIMATED    COST   OF   BAD    KOADS.  13 

the  inquiries  average  only  one  to  300  square  miles, — or  say  about 
three  inquiries  to  two  counties.  This  shows  that  the  attempt  was 
not  on  a  very  elaborate  scale. 

The  Circular  says  that  Table  1  "represents  the  returns  from 
about  1,200  counties";  while  Table  2  shows  that  replies  were  re- 
ceived from  1,061  counties.  The  first  is  equivalent  to  about  one 
county  in  twenty-five,  and  the  second  to  about  one  in  thirty.  In 
either  case,  the  number  of  answers  was  entirely  inadequate  to 
secure  data  representative  of  the  entire  country.  It  is  stated  by 
the  Director  of  the  Road  Inquiry  Office  that  "  nothing  is  known  as 
to  the  number  of  replies  received  from  each  county. " 

15.  Average  Haul.  The  value  of  the  reply  as  to  the  average 
haul  will  depend  upon  the  manner  of  determining  it.  "  The  Road 
Inquiry  Office  has  no  copy  of  the  letter  of  inquiry."  Apparently 
the  letter  merely  asked  for  the  average  haul,  and  gave  no  instruc- 
tions as  to  the  method  to  be  used  in  deducing  it.  A  man  on  receiv- 
ing such  an  inquiry  and  knowing  that  farm  products  were  hauled 
to  a  certain  town  from  all  distances  up  to  ten  miles,  would  probably 
reply  that  the  average  haul  was  one  half  of  0  +  10,  or  5  miles.  By 
many  trials,  the  writer  has  found  that  in  the  great  majority  of  cases 
this  answer  is  accepted  as  correct ;  while  in  fact  it  is  erroneous,  and 
in  many  cases  greatly  so.  This  method  of  determining  the  average 
haul  does  not  take  into  account  the  number  of  loads  hauled  each 
distance.  The  average  of  the  distances  hauled  is  ordinarily  con- 
siderably more  than  the  average  haul;  and  for  this  reason,  it  is 
probable  that  the  values  in  the  first  column  of  Table  2  are  consider- 
ably too  great.  The  distance  hauled  will  vary  greatly  with  the 
locality.  Farm  products  will  be  hauled  much  farther  to  a  large 
city  than  to  a  small  village ;  certain  kinds  of  products  will  be  hauled 
much  farther  than  others ;  and  the  distance  hauled  will  vary  greatly 
with  the  kind  of  roads.  The  result  for  the  average  haul  to  large 
cities,  where  a  considerable  part  of  the  freight  traffic  on  the  public 
highways  is  hauling  vegetables,  fruit,  etc.,  over  good  stone-roads 
to  market,  even  though  correctly  determined,  is  of  but  little  value 
in  finding  the  cost  of  hauling  the  average  farm  product  to  market. 
Gardeners,  dairymen,  etc.,  live  chiefly  near  large  cities  and  are 
more  interested  in  good  roads  than  the  average  farmer ;  therefore  it 
is  possible  that  the  replies  from  near  large  cities  were  in  undue  pro- 


14  ROAD    ECOMOMICS.  [CHAP.   I. 

portion.  According  to  the  U.  S.  Census  for  1890,  gardeners,  dairy- 
men, florists,  nurserymen,  and  vine-growers  constitute  only  one 
fifty-seventh  of  the  so-called  farming  class ;  and  the  "  area  devoted 
to  raising  fruit  and  vegetables  for  market  is  534,440  acres,"  or  one 
six  hundred  and  sixty-ninth  of  the  area  of  the  cultivated  land. 

The  value  of  the  replies  in  determining  an  average  will  depend 
upon  their  distribution  with  reference  to  productiveness.  One 
part  of  the  state  furnishes  more  traffic  and  is  better  supplied  with 
railroads  than  another.  The  replies  should  be  distributed  pro- 
portionately to  the  amount  of  traffic. 

16.  An  examination  of  a  large-scale  railroad  map  of  the  United 
States  indicates  that  probably  the  average  haul  as  given  in  Table  2 
is  considerably  too  great — at  least  for  the  states  that  furnish  the 
bulk  of  the  traffic.  Portions  of  a  state  may  be  found  which  are 
relatively  at  a  considerable  distance  from  a  railroad  station,  but  in 
nearly  every  case  it  will  be  found  that  throughout  that  area  there 
is  but  little  traffic  on  the  public  highways. 

17.  The  reliability  of  the  value  of  the  average  haul  as  given  in 
Table  2  can  be  approximately  tested  in  another  way.  For  example, 
Illinois  has  an  area  of  56,600  square  miles,  and  in  1895  had  10,752 
miles  of  railways  exclusive  of  sidings  and  second  tracks;  or  1  mile 
of  railroad  for  each  5.2  square  miles  of  area.  Investigations  also 
show  that  the  distance  between  railroad  stations  averages  a  trifle 
under  4.5  miles.  Therefore,  if  wTe  consider  a  strip  of  land  5.2  X  1 
miles  laid  transversely  across  the  railroad  half  way  between  railroad 
stations,  the  maximum  haul  will  then  be  approximately  |  of 
5.2  +  |  of  4.5  =  4.8  miles.  This  may  be  regarded  as  the  average 
maximum  distance  of  haul  in  Illinois  The  average  haul  is  prob- 
ably approximately  half  this,  or  say  2.4  miles.  There  is  a  slight 
error  in  the  above  computation,  since  no  account  is  taken  of  the 
fact  that  the  railroads  cross  each  other  or  that  they  converge 
toward  railroad  centers;  and  for  this  reason  the  above  result  is 
slightly  too  small. 

On  the  other  hand,  the  above  method  is  slightly  in  error  since 
no  account  was  taken  of  water  transportation;  and  for  this  reason 
the  above  result  is  slightly  too  great.  Again,  the  above  result  is 
slightly  too  small,  since  produce  is  hauled  on  wagon  roads  consider- 
able distances  to  large  cities;  but  the  amount  of  these  products  is 


ESTIMATED    COST   OF   BAD   ROADS.  15 

small  as  compared  with  the  total  agricultural  products  (see  §  23). 
Therefore  we  may  conclude  that  the  above  result  is  not  much  too 
small,  although  it  is  less  than  half  that  in  Table  2. 

A  similar  investigation  for  Iowa,  Eastern  Kansas,  Eastern 
Nebraska,  Ohio,  and  Indiana,  leads  to  the  conclusion  that  the 
values  for  the  average  haul  in  Table  2  are  about  twice  too  great. 
The  above  method  of  testing  the  data  in  Table  2  is  not  applicable 
to  states  that  have  considerable  areas  of  untilled  land,  since  under 
these  circumstances  the  distribution  of  railroads  and  railroad  sta- 
tions will  not  be  even  approximately  uniform. 

18.  The  reliability  of  the  data  in  Table  2  may  be  tested  in  an- 
other way.  The  Illinois  Agricultural  Experiment  Station,  in  Bulletin 
No.  50,  published  the  data  received  in  316  replies  from  76  counties 
in  Illinois  concerning  the  cost  of  producing  and  marketing  corn 
and  oats.  According  to  these  data  the  average  distance  hauled 
was  3.2  miles — about  six  tenths  of  the  value  in  Table  2  for  the  aver- 
age haul  in  Illinois. 

19.  Average  Weight  of  Load.  The  weight  of  the  average  load 
varies  chiefly  with  the  grade  of  the  road  and  the  condition  of  its  sur- 
face; and  in  most  localities  the  latter  varies  greatly  with  the  season, 
and  is  not  the  same  for  any  two  successive  years.  Further,  with 
earth  roads  (and  they  constitute  the  great  majority  of  agricultural 
roads  in  this  country)  the  most  of  the  freight  is  hauled  when  the 
roads  are  in  their  best  condition.  For  these  reasons,  it  is  a  matter  of 
considerable  difficulty  to  determine  the  weight  of  the  average  load 
for  any  particular  place,  much  less  for  an  average  of  several  states. 
However,  as  these  data  are  not  directly  used  in  determining  the 
supposed  cost  of  bad  roads,  this  phase  of  the  subject  will  be  dis- 
cussed only  briefly. 

In  the  Bulletin  just  referred  to  the  average  load  in  marketing 
311,845  bushels  of  corn  was  62  bushels.  If  it  were  all  shelled, 
this  is  equivalent  to  1.74  tons  per  load;  and  if  it  were  unshelled, 
it  is  equivalent  at  least  to  2.2  tons  per  load.  As  part  of  it  was 
shelled  and  part  not,  the  average  load  in  this  case  was  somewhere 
between  If  and  2\  tons. 

20.  Cost  per  Ton-mile.  No  details  are  given  as  to  the  method 
employed  in  determining  the  cost  per  ton-mile  of  hauling  crops 
from  farm  to  market.    The  value  of  the  answer  depends  upon  the 


16  ROAD    ECONOMICS.  [CHAP.   I. 

form  of  the  inquiry.  The  author  has  frequently  asked  grain  farmers : 
"  What  is  it  worth  to  haul  crops  to  market?"  In  a  great  majority 
of  cases  the  answer  is  arrived  at  by  counting  the  price  of  a  wagon, 
team,  and  driver  at  $3.00  or  $3.50  per  day  (the  current  price  for  those 
whose  chief  business  is  to  do  teaming),  and  assuming  that  a  team 
will  travel  about  3  miles  per  hour  and  haul  a  load  of  1  to  1J  tons. 
The  result  by  this  method  of  computing  the  cost  per  ton-mile  is  sub- 
stantially the  same  as  that  in  Table  2.  On  changing  the  form  of 
the  question  and  asking:  "What  does  it  really  cost  you?",  the  an- 
swer is  almost  invariably :  "  Nothing.  "  The  average  farmer  is  not 
conscious  that  it  costs  him  anything  to  haul  his  crop  to  market, 
The  great  bulk  of  the  hauling  is  done  when  the  farmer  has  little  or 
nothing  to  do,  or  when  the  delay  of  other  work  is  a  matter  of  little 
moment;  and  in  this  case  the  cost  is  merely  nominal.  The  over- 
looking of  this  fact  is  a  common  and  most  serious  error  of  writers 
on  good-road  economics. 

The  cost  per  ton-mile  as  given  in  Table  2  indicates  that  that 
value  was  obtained  by  assuming  the  wages  of  a  wagon ,  team,  and 
driver  to  be  about  35  cents  per  hour;  that  the  team  travels  about  3 
miles  per  hour;  and  that  the  team  hauls  a  load  only  one  way. 
There  are  two  radical  errors  in  this  method. 

1.  The  price  per  day  is  too  great.  In  the  Bulletin  referred  to 
in  §  18,  the  price  per  day  for  team  and  man  during  the  crop  season, 
as  given  by  the  farmers  themselves,  ranged  from  $1.40  to  $2.74, 
the  average  for  the  76  counties  being  $2.13.  Notice  that  this  is 
the  average  cost  during  the  crop  season,  as  returned  by  316  farmers 
in  76  counties  in  Illinois  Evidently  the  price  per  day  as  returned 
by  the  same  farmers  for  the  dull  season  would  be  considerably  less. 

2.  The  mean  between  the  maximum  and  the  minimum  load  may 
be  one  ton;  but  the  great  bulk  of  teaming  is  done  when  the  roads 
are  at  least  in  fair  condition  when  the  load  is  considerably  more 
than  one  ton.  In  fact,  there  is  very  littJe  of  the  crop  hauled  to 
market  when  the  load  is  one  ton  or  less.  The  author  has  examined 
the  records  of  several  grain  buyers  in  central  Illinois,  where  at  times 
the  roads  are  as  bad  as  anywhere,  and  finds  that  the  average  load 
is  nearly  a  ton  and  a  half.     See  §  19. 

2i.  Non-resident  land  owners  in  central  Illinois  frequently  hire 
corn  delivered  for  9  to  11  cents  per  ton- mile.     This  price  has  ob- 


ESTIMATED    COST    OF    BAD    ROADS.  17 

tained  over  large  areas  for  10  or  15  years.  The  contract  is  usually 
taken  by  the  man  who  does  the  shelling,  he  hiring  farmers  to  do 
the  hauling.  These  prices  obtain  frequently  during  the  corn- 
planting  season,  when  the  farmers  are  most  busy  and  when  the 
roads  are  certainly  not  at  their  best.  During  the  dull  season  farm- 
ers frequently  haul  corn  to  the  farther  market  for  a  difference  in 
price  equivalent  to  6  to  9  cents  per  ton-mile  for  the  hauling.  The 
lower  of  these  prices  usually  obtains  when  the  roads  are  good 
in  the  winter  season  and  there  is  little  or  no  farm  work  to  do. 
Notice  that  the  above  prices  are  practically  one  third  of  those 
given  in  Table  2  for  Illinois. 

The  results  in  Table  2  for  the  cost  per  ton-mile  may  be  approxi- 
mately correct  for  gardeners,  dairymen,  etc.,  who  are  compelled 
to  keep  a  team  upon  the  road  nearly  every  day  of  the  year;  but 
these  are  not  representative  "farmers,"  for,  according  to  the 
Eleventh  Census  of  the  United  States,  there  are  5,281,557  farmers 
and  planters,  and  only  90,470  gardeners,  dairymen,  florists,  nursery- 
men, and  vine-growers;  or,  the  latter  constitute  only  one  fifty- 
seventh  of  the  agricultural  class,  and  work  only  one  six  hundred  and 
sixty-ninth  part  of  the  cultivated  land. 

22.  The  conclusion  is  that  in  Table  2  for  Illinois  the  distance 
hauled  is  twice  too  great  and  the  price  per  ton-mile  is  about  three 
times  too  great;  or  the  "total  cost  from  farm  to  market"  (see 
Table  1)  is  2  X  3  or  6  times  too  great.*  Probably  the  values  for  the 
other  states  are  equally  in  error. 

23.  Cost  of  Marketing  Crops.  Circular  No.  19  of  the  U.  S.  Road 
Inquiry  Office,  previously  referred  to,  determines  that  in  1895  the 
farm  products  amounted  to  219,024,277  tons;  and  assumes  that 
the  farm  products  consumed  on  the  farm  are  offset  by  the  mine  and 
quarry  products,  merchandise,  etc.,  hauled  over  the  public  roads. 
It  is  further  assumed  that  one  quarter  of  the  limber  cut  for  fuel  and 
for  the  mill,  and  all  of  that  used  by  the  railroad,  or  a  total  forest 
product  of  93,525,000  tons,  is  transported  over  the  public  high- 
ways. The  conclusion  is  that  in  1895,  313,349.227  tons  were  hauled 
over  the  highways  of  the  United  States.  The  Circular  assumes 
that  the  average  cost  of  transporting  this  freight  is  $3.02  per  ton 
(the  average  "  cost  from  farm  to  market,"  see  last  line  of  Tables  1 
and  2),  and  that  therefore  the  cost  of  wagon  transportation  in  1895 

*  For  later  data,  see  pages  44a  and  416. 


18  ROAD    ECONOMICS.  [CHAP.   I. 

was  $946,314,665.54.  "  The  immensity  of  this  charge,"  to  quote  the 
Director  of  Road  Inquiry,  "will  be  best  realized  by  comparing  it 
with  the  value  of  all  farm  products  in  the  United  States  for  the 
year  1890— $2,480,170,454.  In  other  words,  the  annual  cost  of  the 
transportation  upon  the  public  highways  of  the  United  States  is 
equal  to  38  per  cent  of  the  value  of  the  farm  crops."  Or,  since  70 
per  cent  of  the  freight  is  assumed  to  be  farm  products,  according 
to  the  above  data,  the  cost  of  hauling  directly  and  indirectly  con- 
nected with  marketing  the  crops  is  38  X  70  =  26.6  per  cent  of  the 
value  of  these  products.  The  total  area  of  the  farms  in  the  United 
States  is  975,000  square  miles,  and  therefore  the  above  cost  of 
wagon  transportation  is  $971  per  square  mile,  or  $1.51  per  acre; 
or,  if  we  include  only  the  improved  land,  the  above  cost  of  wagon 
transportation  is  $1,700  per  square  mile,  or  $2.65  per  acre. 

The  above  conclusions  are  believed  to  be  in  error  for  the  three 
following  reasons: 

1 .  The  Circular  assumes  that  the  farm  products  consumed  on  the 
farm  were  offset  by  the  hauling  of  lumber,  coal,  fertilizers,  mer- 
chandise, etc.,  to  the  farm.  In  the  first  place,  it  is  doubtful  if  there 
are  as  many  tons  of  freight  hauled  to  the  farm  as  there  are  tons  of 
products  consumed  on  the  farm.  In  the  second  place,  the  offset 
ought  not  to  be  allowed,  since  almost  always  the  freight  hauled  to 
the  farm  is  brought  back  when  a  load  of  produce  is  taken  to  town, 
or  is  hauled  back  incidental  to  a  trip  for  some  other  purpose,  or  is 
hauled  when  there  is  nothing  else  to  do.  In  the  third  place,  a 
considerable  part  of  the  farm  product  is  driven  to  market  on 
foot. 

2.  The  average  haul  for  each  of  the  several  states  is  in  error  as 
discussed  in  §  15-18,  and,  in  addition,  the  value  for  the  United 
States  is  in  error  since  no  account  has  been  taken  of  the  relative 
amount  of  traffic  in  the  several  states.  For  example,  Iowa,  with 
its  5.4  miles  haul  and  25,000,000  tons  of  traffic,  has  no  more  weight 
in  the  mean  than  Arizona  with  a  haul  eleven  times  as  great  and  a 
traffic  only  one  hundredth  as  great.  Again,  no  difference  is  made 
between  Illinois,  with  72  per  cent  of  tillable  land,  and  Wyoming, 
with  only  1  per  cent;  and  Delaware  with  an  area  of  2,050  square 
miles  has  the  same  weight  as  Texas  with  an  area  of  265,780  square 
miles. 


ESTIMATED    COST    OF    BAD    ROADS.  19 

3.  The  cost  per  ton-mile  is  too  great  for  the  reasons  stated  in 
§  20-22. 

24.  If  the  cost  of  hauling  the  crops  to  market  were  26.6  per  cent 
of  the  value  of  the  crops,  then  there  should  be  a  marked  difference 
in  the  price  of  land  near  and  remote  from  market.  If  it  costs  26 
per  cent  of  the  value  of  the  produce  to  get  it  to  market,  then  land 
at  the  market  should  be  worth  at  least  26  per  cent  more  than  land 
which  is  the  average  haul  away  from  market.  It  should  be  worth 
more  than  this,  for  there  is  a  considerable  amount  of  travel  in- 
volved besides  that  necessary  to  market  the  crop.  An  investiga- 
tion in  central  Illinois,  where  the  land  is  of  uniform  quality,  shows 
that  the  price  of  land  at  the  market  is  about  5  per  cent  more  than 
that  5  miles  away.  In  a  rough  way  this  shows  that  the  estimates 
of  Tables  1  and  2  are  at  least  something  like  five  or  six  times  too 
great. 

If  the  cost  of  hauling  crops  to  market  is  equal  to  26  per  cent  of 
their  value,  then  there  should  be  a  marked  difference  in  the  rent  of 
land.  The  annual  rent  of  land  varies  from  one  quarter  to  one  half 
the  crop.  If  land  situated  at  the  average  haul  from  the  market 
rents  for  one  quarter  of  the  crop,  then  land  at  the  market  should 
rent  for  half  the  crop,  even  if  the  social  advantage  of  the  latter  is 
not  included.  In  central  Illinois,  where  at  times  the  roads  are  as 
bad  as  anywhere,  there  is  no  appreciable  difference  in  the  renting 
value  between  land  1  mile  and  that  5  miles  from  market.  This 
shows  that  the  conclusions  of  the  above  Circular  are  greatly  in  error.* 

25.  Possible  Annual  Saving.  The  Office  of  Road  Inquiry  in 
Circular  No.  19,  to  which  reference  has  been  made,  estimates  the 
possible  annual  saving  by  road  improvement  as  two  thirds  of 
$943,314,665.54,  or  $628,000,000.  This  estimate  is  based  upon  a 
comparison  of  the  data  in  Circular  No.  19  with  that  on  the  "Cost  of 
Hauling  Farm  Products  to  Market  or  Shipping  Point  in  European 
Countries,  Collected  by  U.  S.  Consular  Agents,"  published  in  Circu- 
lar No.  27  (Feb.  5,  1897)  of  the  Office  of  Road  Inquiry  of  the  U.  S. 
Department  of  Agriculture.     The  average  cost  as  given  in  the  latter 

♦For  a  further  discussion  of  the  Circular  see  the  following :  In  defense  of  the 
Circular,  Engineering  News,  Vol.  34,  p.  410-11 ;  do.,  Vol.  45,  p.  50-51.  Controvert- 
ing the  Circular:  Engineering  News,  Vol.  34,  p.  377-78;  do.,  Vol.  34,  p.  410-11; 
do.,  Vol.  44,  p.  337-44;  do.,  Vol.  45,  p.  48-49;  do.,  Vol.  57,  p.  428;  Supplemental  Note, 
p.  44a  of  this  volume. 


20  ROAD   ECONOMICS.  [CHAP.  I. 

circular  (when  translated)  is  10  cents  per  ton-mile,  and  the  difference 
between  this  and  the  average  stated  in  Table  1  is  15  cents  per  ton- 
mile,  which  is  two  thirds  of  the  average  value  in  Table  1. 

Concerning  the  data  for  America,  notice  that  they  are  taken 
from  Circular  No.  19,  and  are  greatly  in  error  as  has  already  been 
shown. 

Concerning  the  data  for  Europe,  notice  in  the  first  place  that 
they  are  open  to  most  of  the  criticisms  made  against  the  data  in 
Table  2.  In  the  second  place,  the  twelve  results  given  in  Circular  27 
vary  from  4  to  30  cents  per  ton-mile,  which  is  too  wide  a  range  and 
too  few  results  for  an  accurate  determinalion  of  the  average  cost  of 
wagon  transportation  in  Europe.  In  the  third  place,  some  of  the 
results  are  professedly  the  cost  to  transportation  companies,  and 
some  the  cost  to  farmers  to  whom  the  hauling  of  the  crops  to  market 
is  merely  an  incident  of  farm  work.  And,  finally,  the  data  for  the 
cost  of  hauling  not  done  by  transportation  companies  are  for  hauling 
garden  products,  etc.,  to  large  cities,  and  is  therefore  not  repre- 
sentative of  the  cost  of  transporting  general  farm  products  to  mar- 
ket. The  cost  of  wagon  transportation  on  the  very  best  roads  of 
Europe  ought  not  to  be  very  much  less  than  the  ordinary  cost  of 
hauling  farm  crops  to  market  in  America,  for  in  most  cases  the  latter 
is  done  when  the  roads  are  in  fair  or  good  conditions,  and  when  in 
their  best  condition  earth  roads  are  nearly  as  good  as  the  best  stone 
roads. 

26.  It  is  very  unfortunate  that  the  conclusions  from  the  two  Cir- 
culars referred  to  above,  have  been  so  generally  accepted  by  speakers 
and  writers  upon  good-road  economics.  Country  roads  are  used 
chiefly  by  farmers,  and  if  improvements  are  made  they  must  be 
paid  for. largely,  if  not  entirely,  by  farmers;  and  therefore  the  co- 
operation of  farmers  must  be  secured  before  any  improvement  of 
the  country  roads  is  possible.  Farmers  instinctively  know  that 
conclusions  such  as  deduced  above  from  Table  2  are  ridiculous,  and 
not  unnaturally  distrust  the  motives  prompting  the  argument,  and 
are  hostile  to  all  propositions  for  road  improvement  supported  by 
such  arguments. 

Further,  it  is  not  possible  to  determine  either  the  cost  of  wagon 
transportation  or  the  financial  value  of  road  improvement  in  the 
wholesale  manner  proposed  in  the  above  Circulars.     The  cost  of 


TRACTIVE    RESISTANCE.  21 

haul  and  the  value  of  improved  roads  varies  greatly  with  local  con- 
ditions; and  ordinarily  it  will  be  found  that  the  probable  saving  in 
cost  of  wagon  transportation  alone  is  not  sufficient  to  justify  any 
radical  road  improvements.  However,  financial  profit  is  only  one 
of  the  advantages  of  good  roads  (see  §  1-3). 

27.  TRACTIVE  RESISTANCE.  The  resistance  to  traction  of 
a  vehicle  on  a  road  consists  of  three  independent  elements:  axle 
friction,  rolling  resistance,  and  grade  resistance. 

28.  Axle  Friction.  The  resistance  of  the  hub  to  turning  on  the 
axle  is  the  same  as  that  of  a  journal  revolving  in  its  bearing,  and  has 
nothing  to  do  with  the  condition  of  the  road  surface.  The  co-effi- 
cient of  journal  friction  varies  with  the  material  of  the  journal  and 
its  bearing,  and  with  the  lubricant.  It  is  nearly  independent  of 
the  velocity,  and  according  to  observations  made  by  the  author 
seems  to  vary  about  inversely  as  the  square  root  of  the  pressure. 
For  light  carriages  when  loaded,  the  co-efficient  of  friction  is  about 
0.020  of  the  weight  on  the  axle;  for  the  heavier  carriages  when 
loaded,  it  is  about  0.015;  and  for  the  ordinary  thimble-skein  Ameri- 
can wagon  when  loaded,  it  is  about  0.012.  The  above  results  are 
for  good  lubrication ;  if  the  lubrication  is  deficient,  the  axle  friction 
is  two  to  six  times  as  much  as  above.  The  above  figures  agree 
reasonably  well  with  results  obtained  for  journal  friction  of  ma- 
chines. Apparently  the  value  of  this  co-efficient  in  Morin's  experi- 
ments (§  34)  was  0.065.*  The  greater  axle  friction  is  probably  due 
to  the  inferior  mechanical  construction  of  French  carriages  and 
wagons  of  that  date. 

The  tractive  power  required  to  overcome  the  above  axle  friction 
for  American  carriages  of  the  usual  proportions  is  about  3  to  3J  lb. 
per  ton  of  the  weight  on  the  axle;  and  for  truck  wagons,  which 
have  medium-sized  wheels  and  axles,  is  about  3|  to  4^  lb.  per  ton. 

29.  Rolling  Resistance.  The  resistance  of  a  wheel  to  rolling 
along  on  a  road  is  due  to  the  yielding  or  indentation  of  the  road, 
which  causes  the  wheel  to  be  continually  climbing  an  inclination. 
The  resistance  is  measured  by  the  horizontal  force  necessary  at  the 
axle  to  lift  the  wheel  over  the  obstacle  or  to  roll  it  up  the  inclined 
surface;  and  varies  with  the  diameter  of  the  wheel,  the  width  of  the 

*  Lowe's  Strassebaukunde,  page  75.     Wiesbaden,  1895. 


22 


ROAD   ECONOMICS. 


[CHAP.   I. 


tire,  the  speed,  the  presence  or  absence  of  springs  on  the  vehicle, 
and  the  nature  of  the  road  surface. 

30.  Diameter  of  Wheel.  The  rolling  resistance  varies  inversely 
as  some  function  of  the  diameter  of  the  wheel,  since  the  larger  the 
wheel  the  less  the  force  required  to  lift  it  over  the  obstruction  or  to 
roll  it  up  the  inclination  due  to  the  indentation  of  the  surface. 
Table  3  shows  the  results  obtained  by  Mr.  T.  I.  Mairs  at  the 
Missouri  Agricultural  Experiment  Station,*  with  three  different- 
sized  wheels.  The  50-inch  represents  44-inch  front  wheels  and 
56-inch  hind  wheels;  the  38-inch  represents  36-inch  front  and 
40-inch  hind  wheels;  and  the  26-inch  represents  24-inch  front  and 
28-inch  hind  wheels.  The  tires  were  6  inches  wide.  The  load  was 
practically  If  tons  in  each  case. 

TABLE  3. 

Effect   of   Size   of  Wheels  on  Tractive  Resistance.* 

Resistances  in  Pounds  per  Ton. 


Ref. 

No 

Description  of  Road  Surface. 

Mean  Diameter  of  Front 
and  Rear  Wheels. 

50*s 

38*. 

26". 

1 
2 

Macadam:  slightly  worn,  clean,  fair  condition. 

Gravel  road:  dry,  sand  1"  deep,  some  loose 

stones  . .          

57 

84 

123 
69 
101 
132 
173 
178 
252 

61 

90 

132 
75 
119 
145 
203 
201 
303 

70 
110 

3 

Gravel  road:    up  grade  2.2%,   \"  wet  sand, 
frozen  below.  .          

173 

4 

Earth  road   dry  and  hard                  

79 

5 
6 

7 
8 
9 

"         "       ¥  sticky  mud,  frozen  below,  rough 

Timothy  and  blue-grass  sod:  dry,  grass  cut.  .  . 

"           "           "             "      wet  and  spongy . 

Corn-field:  flat  culture,  across  rows,  dry  on  top 

Plowed  ground :  not  harrowed,  dry  and  cloddy 

Average  value  of  the  tractive  power 

139 
179 
281 
265 
374 

10 

130 

148 

186 

Morin  concluded  that  the  resistance  varies  inversely  as  the  first 
power  of  the  diameter  of  the  wheel;  Dupuit.  that  it  varies  as  the 
square  root;  and  Clarke  claims  that  it  varies  as  the  cube  root.f 
According  to  some  experiments  made  in  England  in  1874, J  the 


*  Missouri  Agricultural  Experiment  Station,  Bulletin  No.  52.  Columbia,  1902. 
f  Clarke's  Construction  of  Roads  and  Streets,  p.  294.    London,  1890. 
%  Clarke's  Manual  of  Rules,  Tables  and  Data  for  Mechanical  Engineers,  p.  962. 
London,  1877. 


TRACTIVE    RESISTANCE.  23 

tractive  resistance  varied  more  rapidly  than  the  first  power  of  the 
diameter  of  the  wheels.  The  mean  results  in  Table  3  vary  nearly 
inversely  as  the  square  root  of  the  mean  diameter — certainly  more 
nearly  than  as  either  the  first  power  or  the  cube  root.  For  obvious 
reasons,  the  experiments  can  not  be  very  exact;  and  apparently 
the  tractive  resistance  varies  differently  for  different  surfaces.  The 
exact  determination  of  the  law  of  variation  is  of  no  great  importance. 

31.  Width  of  Tire.  If  the  wheel  cuts  into  the  road  surface,  the 
tractive  resistance  is  thereby  increased ;  but  with  surfaces  for  which 
there  is  little  or  no  indentation,  the  traction  is  practically  inde- 
pendent of  the  width  of  tire. 

Table  4,  page  24,  shows  the  results  of  an  elaborate  series  of 
experiments  by  the  Missouri  Agricultural  Experiment  Station.* 
The  load-in  each  case  was  1  ton.  These  results  show  that  on  poor 
macadam,  poor  gravel,  and  compressible  earth  roads,  and  also  on 
agricultural  land,  the  broad  tire  gives  less  resistance  except  as 
follows:  (1)  when  the  earth  road  is  sloppy,  muddy,  or  sticky  on  top 
and  firm  underneath;  (2)  when  the  surface  is  covered  with  a  very 
loose  deep  dust  and  is  hard  underneath;  (3)  when  the  mud  is  very 
deep  and  so  sticky  that  it  adheres  to  the  wheel;  or  (4)  when  the 
road  has  been  rutted  with  the  narrow  tire.  The  last  conclusion 
was  established  by  a  large  number  of  experiments  not  included  in 
Table  4,  page  24. 

Table  5,  page  25,  gives  data  on  the  effect  of  width  of  tire  upon 
the  tractive  power,  obtained  by  the  Studebaker  Bros.  Manufactur- 
ing Co.,  South  Bend,  Ind.,  in  1892,  with  an  ordinary  3  J-inch  thimble- 
skein  wagon.  Notice  that  on  a  hard  and  incompressible  road  sur- 
face, e.  g.,  wood  block  pavement  and  gravel,  the  narrower  tire 
draws  the  easier;  while  upon  the  soft  or  spongy  surface  the  wider 
tire  draws  the  easier. 

Morin  experimented  (see  §  34)  with  tires  2J,  4J,  and  6|  inches 
wide ;  and  concluded  that  on  a  solid  road  or  pavement  the  resistance 
was  independent  of  the  width  of  the  tire,  but  on  a  compressible 
surface  the  resistance  decreased  as  the  width  of  the  tire  increased, 
the  rate  depending  upon  the  nature  of  the  surface. 


*  Missouri  Agricultural  Experiment  Station,  Bulletin  No.  39.  Columbia,  Mo., 
July  1897. 


24 


ROAD    ECONOMICS. 


[CHAP.   I. 


TABLE  4. 

Tractive  Resistance  of  Broad  and  Narrow  Tires.* 

Resistances  in  Pounds  per  Ton. 


Description  of  the  Road  Surface. 


Width  of  Tire. 


ir. 


Broken  Stone  Road  : 

Hard,   smooth,   no    dust,   no    loose  stones, 
nearly  level 

Gravel  Road  : 

Hard  and  smooth,  few  loose  stones  size  of 

black  walnuts 

Hard,  no  ruts,  large  quantity  of  sand  which 

prevented  packing 

New,  gravel  not  compact,  dry 

Wet,  loose  sand  1"  to  2\"  deep 

Earth  Roads  : 

Loam, — dry,  loose  dust  2"  to  3"  deep 

"     hard,  no  dust,  no  ruts,  nearly 

level 

"         stiff  mud,  drying  on  top,  spongy  be 

low 

"         mud  2\"  deep,very  sticky,  firm  below 

Clay, — sloppy  mud  3"  to  4"  deep,  hard  below 

"        dry  on  top  but  spongy  below,  narrow 

tires  cut  in  6"  to  8" 

"        dry  on  top  but  spongy  below 

"        stiff  deep  mud 

Mowing  Land  : 
Timothy  sod, — dry,  firm,  smooth,  narrow  tire 

1  cuts  in  1" 

"  "       moist,  narrow  tire  cuts  in  34" 

"  "       soft  and  spongy,  grass  and 

stubble    3"    high,    narrow 

tire  cuts  in  6" 

Pasture  Land : 

Blue-grass  sod, — dry,  firm,  smooth 

"           "        soft,  narrow  tire  cuts  in  3'' . 
"  "        narrow  tire  cuts  in  4" 

Stubble  Land  : 
Corn  stubble, — no  weeds,  nearly  dry  enough 

to  plow 

"  "  some  weeds  and  stalks,  dry 

enough  to  plow 

"  "  in  autumn,  dry  and  firm 

Plowed  Land  : 

Freshly  plowed,  not  harrowed,  surface  rough 
"  "       harrowed,  smooth,  compact . 


121 


182 

239 
330 
246 

1?7 

90 

149 

497 
251 

286 

472 
618 
825 

317 
421 


569 

218* 

420 

578 


631 

423 

404 

510 
466 


98 


134 

157 

260 
254 

fiff- 

106 

109 

307 
325 
406 

422 
464 
551 


229 
305 


327 

156 
273 
436 


418 

362 
256 

283 
323 


*  Missouri  Agricultural  Experiment  Station,  Bulletin  No.  39,  July  1897. 


TRACTIVE    RESISTANCE. 


25^ 


TABLE  5. 

Effect  of  Width  of  Tire  upon  Tractive  Power.* 

Resistances  in  Pounds  per  Ton, 


Description  of  the 
Road  Surface. 

Diameters  of  the  Front  and  Rear  Wheels  Respectively. 

Ref. 
No. 

3'  6*  and 

3'  10". 

3'  6"  and 
3'  10". 

3'  8"  and  (  3'  6"  and 
4'    6".       |      3'  10", 

3'  V  and 
4' 6*. 

Width  of  the  Tire. 

W 

4" 

IV 

4" 

.  W 

4" 

IF 

3" 

i 

IF 

3" 

1 

Sod 

283 
152 

239 
152 

189 
114 
265 

228 

2 

Earth  Road,  hard. . 

"      muddy 

Sand  Road,  hard .  . 

deep.. 

Gravel  Road,  good. 

199 
371 

108 
243 
162 
351 

114 

3 

268 
171 

304 
164 

236 
141 

254 

168 

228 

4 

5 

6 

98 
61 

117 

70 

83 
35 

80 
46 

66 
28 

76 

7 

Wood  Block,  round 

51 

49 

54 

38 

*  Pamphlet  by  Studebaker  Bros.  Manufacturing  Co.,  South  Bend,  Ind.,  1892. 

For  a  further  discussion  of  the  relative  merits  of  broad  and 
narrow  tires/ see  §  188-90. 

32.  Effect  of  Speed.  The  rolling  resistance  increases  with  the? 
velocity ,  owing jto  the  effect  of  the  shocks  or  concussions  produced 
by  the  irregularities  of  the  road  surface.  This  increase  is  less  for 
vehicles  having  springs  than  for  those  not  having  them,  and  is  alsa 
less  for  smooth  road  surfaces  than  for  rough  ones. 

Table  6,  page  26,  is  a  summary  of  Morin's  results  (see  § .  34) 
showing  the  effect  of  a  variation  of  speed  for  vehicles  provided 
with  springs.  In  a  rough  way  the  three  speeds  are  2f,  5,  and  7i 
feet  per  second,  or  about  2,  4,  and  6  miles  per  hour  respectively- 
According  to  these  results  the  resistance  on  broken-stone  roads  in- 
creases roughly  as  the  fourth  root  of  the  speed,  and  on  stone-block 
pavement  about  as  the  square  root.  For  springless  vehicles  the 
increase  would  be  greater.  The  above  is  for  metal  tires ;  for  pneu- 
matic tires  there  is  very  little  increase  of  resistance  with  increase; 
of  speed.* 

The  preceding  data  refer  to  the  effect  of  speed  upon  the  tractive* 
power  after  the  load  is  in  motion.  It  requires  from  two  to  six  or 
eight  times  as  much  force  to  start  a  load  as  to  keep  it  in  motion  at. 


Proc.  of  Inst,  of  Meeh.  Engrs.  (London),  for  1890,  Part  No.  2,  p.  195. 


26 


ROAD    ECONOMICS. 


[CHAP. 


2  or  3  miles  per  hour.  The  extra  force  required  to  start  a  load  is 
due  in  part  to  the  fact  that  during  the  stop  the  wheel  may  settle 
into  the  road  surface,  in  part  to  the  fact  that  the  axle  friction  at 
starting  is  greater  than  after  motion  has  begun,  and  further  in  part 
to  the  fact  that  energy  is  consumed  in  accelerating  the  load. 

33.  Effect  of  Springs.  Springs  decrease  the  tractive  resistance 
by  decreasing  the  concussions  due  to  irregularities  of  the  road  sur- 
face, and  are  therefore  more  effective  at  high  speeds  than  at  low 
ones,  and  on  rough  roads  than  on  smooth  ones.  Apparently  no 
experiments  have  been  made  upon  the  effect  of  springs ;  but  a  few 
data  on  this  subject  may  be  obtained  by  comparing  the  last  and  the 
sixth  columns  of  Table  7,  page  28. 

TABLE  6. 

Effect   of   Speed    on   Tractive    Power.* 

The  figures  give  the  resistance  in  pounds  per  ton. 


Ref. 
No. 


9 
10 
11 


Description  of  the  Road  Surface. 


Stage  Coach. 


Carriage. 


Walk 
2. 


Broken  Stone  Road  : 

Good  condition,  dry  and  compact  . . . 

Very  firm,  large  stones  visible ■. . 

Little  moist,  or  little  dirty 

Firm,  little  soft  mud 

"       ruts  and  much  mud 

Portions  worn  out,  thick  mud 

Much  worn,  ruts  3"  deep,  thick  mud . 


—Very  bad,  ruta  1"  doop,  vory  rough- rr"T11fr£ 


Stone  Block  Pavement : 

Very  smooth,  narrow  joints. 

Fair  condition,  dry 

Moist,  covered  with  dirt... . , 


42 
59 
49 
77 
95 
112 
T46 


Trot. 

4 


49 
75 
75 

92 
108, 
127' 
161 

■Wfr 


48 

52 

'49 


Fast 
frot. 


50 
81 
88 
100 
117 
134 
169 


41 
58 
48 
76 
93 
110 
145 


55- 

61 
56 

J  It 


31 
34 
44 


48 

73 

74 

91 

108 

126 

160 


1 62  ~ '"""mJ"i. 


Fast 
Trot. 


49 

81 

88 

99 

116 

132 

168 


7J>: 

54 

,67 

67 


34.  Different  Road  Surfaces.  Immediately  before  and  shortly 
after  the  introduction  of  railroads,  European  engineers  made  many 
experiments  on  the  force  necessary  to  draw  different  vehicles  ov'er 
various  surfaces.     The  experiments  by  Morin;*  made  in  1837-41  for 


♦Experiences  sur  le  tirage  des  ventures  et  sur  les  effets  destructeurs  qu'elles 
exereent  sur  les  routes,  executees  en  1837  et  1838  par  ordre  du  Mioistre  de  la  Guerre, 
et  en  1839  et  1841  par  ordre  du  Ministre  des  Travaux  Publics,.  A.  Morin.    Paris,  1842. 


TRACTIVE    RESISTANCE. 


27 


the  French  Government,  were  much  the  most  elaborate  and  appear  to 
have  been  made  with  great  care.  Table  7,  page  28,  is  a  summary  of 
Morin's  results  showing  the  tractive  resistance  for  different  vehicles 


TOP  VIEW 


.  BOTTOM  VIEW 
Fig.  1. — Baldwin  Dynograph. 


on  various  road  surfaces.  The  table  represents  about  700  experi- 
ments. Any  vertical  column  shows  the  resistance  for  a  particular 
vehicle  on  the  various  road  surfaces,  and  any  horizontal  line  shows 
the  resistance  on  a  particular  road  surface  for  different  vehicles. 


28 


ROAD    ECONOMICS. 


[CHAP.   I. 


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TRACTIVE    RESISTANCE. 


29 


35.  Table  8  shows  data  obtained  by  the  author.  The  tractive 
power  was  determined  with  a  Baldwin  dynograph,  Fig.  17  page  27. 
The  instrument  consists  of  two  long  flat  springs  fastened  together 
at  their  ends  and  having  their  centers  slightly  farther  apart  than 
their  ends.  One  end  of  the  apparatus  is  attached  to  the  wagon, 
and  the  team  is  hitched  to  the  other.  The  pull  of  the  team  causes 
the  centers  of  the  flat  springs  to  approach  each  other.  One  spring 
supports  a  graduated  disk,  and  the  other  is  connected  to  an  index 
arm  which  is  pivoted  at  the  center  of  the  disk.  From  one  end  of 
this  index  arm,  the  pull  can  be  read  directly  from  the  graduated 
disk.     There  are  two  extra  index  arms — one  to  indicate  the  maxi- 

TABLE  8. 
Tractive  Resistance  on  Level  Pavements. 


Ref. 
No. 


1 
2 
3 
4 
5 
6 
7 
8 
9 
10 

11 
12 

13 

14 
15 

16 

17 


IS 
19 
20 
21 
22 
23 
24 

2o 

2*; 


Location  and  Description  of  the  Pavement. 


Asphalt.  Chicago — Calumet  Ave.,  bet.  43d  and  44th  Sts.;  smooth,  clean. 

no  cracks ,  52°  F \ 

Chicago — Calumet  Ave.,  bet.  43d  and  44th  Sts.;  smooth,  ciean. 

no  cracks,  84°  F '. 

Chicago — Washington  Boul.,  bet.  Haisted  and  Green  Sts. ;  smooth 

clean,  no  cracks.  42°  F 

Brick.  Champaign — University  Ave.,  west  of  New  St.;  3  X  9-in.  brick  on 

concrete,  corners  rounded,  sand  filler,  not  worn   clean 

Champaign — Second  South  St.;  same  as  No.  4,  except  newer  and 

covered  with  \  in.  of  dust 

Champaign — First  South  St.:  same  as  No.  4.  except  cement  filler 

just  completed 

Chicago— Peoria  St..  between  Washington  and  Randolph;  2\  X  8- 

in.  brick  on  concrete,  pitch  filler   new 

Chicago — Laurel  St.   Stock  Yards;  3  X  8-in.  brick  on  gravel  and 

cinders,  sand  filler   corners  not  rounded 

Chicago — Exchange  Ave..   Stock  Yards;  2\  X  8-in.  brick  on  sand 

and  old  macadam,  tar  filler,  new 

Granite  block .  Chicago — Exchange  Ave.,  Stock  Yards;  smoothly  dressed 
3  X  9-in.  blocks  on  concrete,  joints  \  inch.,  tar  filler,  not 

worn 

Chicago — Randolph  St.,  between  Desplaines  and  Haisted: 
smoothly  dressed  blocks  on  concrete,  pitch  filler,  new..  .  . 
Chicago — Haisted  St..  between  Randolph  and  Washing- 
ton; ordinary  granite.  9  years  old 

Macadam-  Chicago — Michigan  Ave.,  between  42d  and  43d  Sts.;  granite 

top.  no  dust,  no  mud 

Plank  road:  Chicago — Packer's  Ave..  Stock  Yards;  oak  plank,  3  X  12-in.. 

nearly  new 

Exactly  same  as  above  after  worn  down  \  inch  in  many  places. 

clean 

Substantially  same  as  above-  covered  with  ±  inch  fine. loose  dirt 

Steel  wheelway   Chicago— Transit  Ave.,  Stock  Yards;  8-in.  ll^-lb.  channel 

on  2  X  8-in.  pine,  that  on  macadam,  covered  with  \  inch 

powdered  stone 

Same  when  scraped  with  a  shovel 

Same  when  covered  with  \  inch  fine  dust 

Wood  block:  Rectangular  blocks   3  X  12-in.    considerably  worn 

Cylindrical  cedar  block  covered  with  A-  inch  sihcia  pea  gravel 
Exactly  same  as  above  covered  with  \  inch  crushed  gravel .  . 
Cylindrical  cedar  block,  clean  blocks  slightly  convex  on  top 
Cylindrical  cedar  block  on  2-inch  plank  and  2  inches  of  sand 

clean ,  not  worn . 

Same  as  above :  clean   slightly  worn 

Same  as  above;  clean,  considerably  worn 


Pounds 
_per 
Ton. 


37 
70 
34 
17 
31 
25 
24 
37 
25 

29 
30 
36 
18 
32 

38 

40 


40 

19 

28 

36 

90  >. 

.50 

53 

37 
51 
54 


30  ROAD    ECONOMICS.  [CHAP.   I. 

mum  power  developed  and  one  to  indicate  a  rough  average.  The 
former  (the  upper  one  in  Fig.  1)  is  simply  pushed  around  by 
the  main  index  arm  and  is  left  at  the  highest  point.  The  latter  (the 
middle  arm  in  Fig.  1)  has  a  transverse  slot  in  which  plays  a  stud  on 
the  main  index  arm.  When  making  an  experiment  the  main  index 
arm  is  continually  in  motion,  and  the  position  of  the  auxiliary  arm 
roughly  indicates  the  average  power  exerted.  The  end  of  the  index 
arm  opposite  the  graduated  arc  records  the  amount  of  tractive  resist- 
ance upon  a  strip  of  paper  which  is  wound  from  one  cylinder  to 
another  by  clock-work  located  behind  the  lower  right-hand  corner 
of  Fig.  1.  The  autographic  record  is  more  accurate  than  the  indi- 
cated reading. 

The  wagon  employed  was  the  usual  thimble-skein  four-wheel 
farm  wagon  with  a  2-inch  tire.  Experiments  3;  4,  and  5  were  made 
with  wheels  averaging  42^  inches  in  diameter,  and  the  remainder 
with  wheels  averaging  47  inches. 

36  From  a  study  of  the  preceding  experiments  and  also  others 
not  here  described,  it  is  concluded  that  the  average  tractive  resist- 
ance on  different  road  surfaces  is  about  as  in  Table  9,  page  31 ,  which 
is  given  for  use  in  comparing  different  roads  and  pavements. 

37.  Grade  Resistance.  This  is  the  force  required  on  a  grade  to 
keep  the  load  from  rolling  down  the 
slope.  It  is  independent  of  the  na- 
ture of  the  road  surface,  and  depends 
only  upon  its  angle  of  inclination. 

In  Fig.  2,  P  is  the  grade  resist- 
ance, and  W  is  the  weight  of  the  wheel 
and  its  load.     From  the  diagram  it  is 
easily  seen  that  P  =  WxB  C  +  A  C.     For  all  ordinary  cases,  A  C 
may  be  considered  as  equal  to  A  B,  and  then  P=WxB  C  +  A  B. 

The  preceding  analysis  is  approximate  for  three  reasons:  (1) 
assuming  A  C  =  A  B,  i.  e.,  assuming  the  sine  ol  inclination  to  be 
equal  to  the  tangent;  (2)  assuming  the  normal  pressure  on  the 
inclined  road  surface  to  be  equal  to  the  weight,  i.  e.,  assuming  the 
cosine  of  the  inclination  to  be  unity;  and  (3)  neglecting  the  fact 
that  the  hind  wheels  carry  a  greater  proportion  of  the  load  on  an 
inclination  than  on  the  level.  The  resulting  error,  however,  is 
wholly  inappreciable. 


POWER    OF   A    HORSE. 


31 


TABLE  9. 
Standard  Tractive  Resistance  of  Different  Roads  and  Pavements. 


Ref. 

Kind  of  Road  Surface. 

Tractive  Resistance. 

No. 

Pounds  per  Ton. 

In  Terms  of  Load. 

1 

Asphalt — artificial  sheet 

30-  70 
15-  40 
50-100 
50-200^ 
50-100 
20-100 
30-  50 
100-200 
30-  80 
15-  40 
30-  50 
40-  80 

l   _  l 

2 

Brick 

T¥  3  ~  3V 
To" "  ¥ff 

3 

Cobble  stones 

4 
5 

Earth  roads — ordinary  condition. 
Gravel  roads 

6 

Macadam           

1         l 

F0~-T0" 

lis  ~  F0" 
1    _    1 

5  0  ~?T 

7 

Plank  road   

8 
9 

Sand — ordinary  condition 

Stone  block 

10 

Steel  wheelway 

11 
12 

Wood  block — rectangular 

"         "         cylindrical 

Grades  are  ordinarily  expressed  in  terms  of  the  rise  or  fall  in  feet 
per  hundred  feet,  or  as  a  per  cent  of  the  horizontal  distance.  If 
A  B  be  100  feet,  then  the  number  of  feet  in  B  C  is  the  per  cent  of  the 
grade;  and  therefore  the  grade  resistance  is  equal  to  the  load  mul- 
tiplied b}'  the  per  cent  of  the  grade.  Or  the  grade  resistance  isr 
equal  to  20  pounds  per  ton  multiplied  by  the  per  cent  of  the  grade. 

38.  POWER  OF  A  HORSE.  The  horizontal  pull  which  a  horse  can. 
exert  depends  upon  its  weight,  its  form  or  build,  the  method  of 
hitching,  the  foothold  afforded  by  the  surface,  the  speed,  the  length 
of  duration  of  the  effort,  the  rest-time  between  efforts,  and  the  tax 
upon  the  future  efficiency  of  the  horse.  The  chief  of  these  are  the 
weight,  the  speed,  and  the  length  of  the  effort. 

Horses  vary  in  weight  from  800  to  1,800  pounds.  The  larger 
horses  do  not  usually  travel  more  than  2h  or  3  miles  per  hour.  With 
reasonably  good  footing  a  horse  can  exert  a  pull  equal  to  one  tenth 
of  his  weight  at  a  speed  of  2\  miles  per  hour  (3f  feet  per  second) 
for  10  hours  per  day  for  6  days  per  week  and  keep  in  condition. 
This  is  a  common  rate  of  exertion  by  farm  horses  in  pulling  plows, 
mowers,  and  other  agricultural  implements.  On  this  baiis  a  1650- 
pound  horse  would  develop  550  foot-pounds  per  second  (the  con- 
ventional horse-power),  and  16,500,000  foot-pounds  per  day.  A 
lighter  horse  will  exert  a  proportionally  less  force.  This  may  be 
considered  about  the  limit  of  endurance.     If  the  time  of  the  effort 


32  ROAD    ECONOMICS..  [CHAP.   I. 

is  decreased,  the  draft  may  be  proportionally  increased;  or  if  the 
speed  is  increased,  the  draft  must  be  decreased  in  a  like  proportion. 
In  other  words,  the  foot-pounds  of  energy  that  can  be  developed  per 
day  by  any  particular  horse  is  practically  constant. 

The  maximum  draft  for  a  horse  is  about  half  of  his  weight, 
although  horses  have  been  known  to  exert  a  pull  of  two  thirds  of 
their  weight.  Most  horses  can  exert  a  tractive  power  equal  to  half 
their  weight,  at  a  slow  walk  for  about  100  feet.  On  the  road  in 
emergencies,  as  in  starting  the  load  or  in  overcoming  obstacles,  a 
horse  id  ay  be  expected  to  exert  a  pull  equal  to  half  his  weight,  but 
at  this  rate  he  would  develop  a  day's  energy  in  about  2  hours;  and 
consequently  if  he  is  expected  to  work  all  day,  he  should  not  be 
called  upon  to  exert  his  maximum  power  except  for  a  short  time. 
Similarly,  a  horse  can  exert  a  draft  equal  to  one  quarter  of  his  weight 
for  a  longer  time.  The  working  tractive  power  of  a  horse  may  be 
taken  as  one  tenth  of  its  weight,  with  an  ordinary  maximum  of  one 
quarter,  and  in  great  emergencies  a  maximum  of  one  half  its  weight. 

39.  Increasing  the  number  of  horses  does  not  increase  the  power 
proportionally — for  somewhat  obvious  reasons.  It  is  stated  that 
for  a  two-horse  team  the  efficiency  of  each  horse  is  about  95  per 
cent;  for  a  three-horse  team,  about  85  per  cent.  Of  course  such 
data  are  not  much  more  than  guesses. 

40.  Effect  of  Grade.  The  effective  tractive  power  of  a  horse 
upon  an  inclined  road  surface  is  decreased  by  the  fact  that  the 
horse  must  lift  his  own  weight  up  the  grade.  If  T  =  the  tractive 
power  on  a  level,  W  =  the  weight  of  the  horse,  t  =  the  tractive 
power  on  a  grade  in  per  cent  of  the  weight  of  the  horse,  and  g  =  the 
per  cent  of  the  grade  or  inclination,  then,  with  sufficient  accuracy, 

T=;tW-gW=(t-g)W (1) 

If  it  be  assumed  that  the  average  working  tractive  power  of  the 
horse  is  one  tenth  of  its  weight,  then  £  =  10  per  cent;  and  equation 
(1)  shows  that  on  a  1  per  cent  grade  the  horse  can  exert  an  effective 
tractive  power  of  9  per  cent  of  his  weight,  and  also  that  he  will  be 
able  to  carry  his  own  weight  up  a  10  per  cent  grade.  If  it  be  as- 
sumed that  the  horse  exerts  a  tractive  power  equal  to  20  per  cent  of 
his  weight,  then  equation  (1)  shows  that  on  a  10  per  cent  grade  he 
can  take  his  own  weight  up  and  in  addition  exert  a  tractive  power  of 


POWER   OF   A    HORSE.  35 


10  per  cent  of  his  weight  upon  the  load.  By  assigning  values  to  t 
and  g,  equation  (1)  readily  shows  the  effective  draft  of  a  horse 
upon  any  grade. 

Equation  (1)  is  not  mathematically  correct,  since  it  assumes 
that  the  weight*  of  the  horse  is  always  normal  to  the  road  surface. 
However,  the  formula  is  sufficiently  accurate  for  use  in  comparing: 
the  relative  tractive  power  of  a  horse  on  different  grades  (see  §  41). 
At  best  such  a  formula  can  be  only  approximate,  since  the  tractive 
power  varies  greatly  with  the  foothold. 

41.  Maximum  Load  on  a  Grade.  On  a  grade  the  effective  trac- 
tive power  as  given  by  equation  (1)  is  used  up  in  moving  the  load 
over  the  road  surface  and  in  lifting  the  load  vertically.  If  L  =  the 
load,  and  ju.  the  co-efficient  of  road  resistance,  then 

(t-g)W=  ML  +  gL.     ......    (2) 

and 

L^-^-W .     (3) 

m-+  g 

Equation  (3)  gives  the  load  that  a  horse  can  draw  up  any  road 
surface. 

Table  10,  page  34,  is  computed  from  equation  (3)  for  a  value  of 
/  equal  to  one  tenth  of  the  weight  of  the  horse.  The  top  line  of  the 
table  shows  the  loads  that  a  horse  can  draw  on  the  level  on  the 
various  road  surfaces ;  and  any  column  of  the  table  shows  the  load 
that  a  horse  can  pull  on  any  grade  for  that  particular  road  surface- 
As  showing  the  different  effects  of  grades  upon  different  roads,, 
notice  that  on  a  muddy  earth  road  a  1  per  cent  grade  reduces  the 
load  less  than  one  tenth,  while  on  asphalt  a  1  per  cent  grade  reduces 
the  load  more  than  one  half;  or,  again,  notice  that  with  a  5  per 
cent  grade,  on  iron  rails  the  load  is  less  than  one  twentieth  of  the 
load  on  the  level,  while  on  the  best  earth  road  the  load  is  one  fifth 
of  that  on  the  level. 

Table  10  shows  the  load  a  horse  can  draw  upon  different  grades 
and  different  road  surfaces  when  exerting  a  uniform  pull  equal  to- 
one  tenth  of  its  weight.  If  we  desire  to  know  the  maximum  load 
which  a  horse  can  draw  up  any  grade,  we  must  insert  in  equation 
(3)  the  maximum  value  of  t  and  compute  the  corresponding 
value  of  L.     The  value  of  rto  be  used  in  this  computation  will 


*^ 


34 


ROAD   ECONOMICS. 


[CHAP.   I. 


TABLE  10. 

Effect  of  Grade  upon  the  Load  a  Horse  can  Draw  on  Different  Roads. 

The  Load  is  in  terms  of  the  Weight  of  the  Horse. 


Earth  Road. 

Rate  of 
Grade. 

Iron 
Rails. 

Sheet 
Asphalt. 

Broken 
Stone . 

Stone 
Block. 

Ref.  No. 

per  cent. 

^  =  305 

M  =  iJo. 

/*  =  Vo- 

M=E\». 

Best 

Spongy. 
M=ao- 

Muddy. 

1 

0. 

20,00 
6  00 

10.00 

6.00 

5.00 

3.00 

2.00 

1.00 

2 

1 

4.50 

3.33 

3.00 

2.09 

1.50 

0.91 

3 

2 

3.20 

2.67 

2.16 

2.00 

1.51 

1.14 

0.67 

4 

3 

2.00 

1.75 

1.49 

1.40 

1.11 

0.87 

0.54 

5 

4 

1.33 

1.20 

1.05 

1.00 

0.82 

0.66 

0.43 

6 

5 

0.91 

0.83 

0.75 

0.71 

0.60 

0.50 

0.33 

7 

6 

0.62 

0.57 

0  52 

0.50 

0.43 

0.36 

0.25 

8 

7 

0.40 

0.38 

0.34 

0.33 

0.29 

0.25 

0.18 

9 

8 

0.24 

0.22 

0.21 

0.20 

0.18 

0.15 

0.11 

10 

9 

0.15 

0.10 

0.09 

0.09 

0.08 

0.07 

0.05 

11 

10 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

TABLE  11. 

Load  which  a  Horse  can  Draw  on  a  Grade  in  Terms   of  the  Load  on 
the  Level   when  Exerting  a  Uniform   Force  Equal   to  One  Tenth 

of  its  Weight. 


Earth  Road. 

Rate  of 
Grade, 

Iron 
Rails. 

Sheet 
Asphalt 

Broken 
Stone 

Stone 
Blocks. 

Ref.  No. 

per  cent. 

^  =  2&0- 

M=ita- 

l*  =  BV 

l*  =  *V 

Best. 

M=3V 

Spongy 
(*■  =  A- 

Muddy. 

1 

0 

1.00 

1.00 

1.00 

1.00 

1.00 

1.00 

1.00 

2 

1 

0.30 

0.45 

0.56 

0.60 

0.62 

0.75 

0.91 

3 

2 

0.16 

0.27 

0.36 

0.40 

0.50 

0.57 

0.67 

4 

3 

0.10 

0.18 

0.25 

0.28 

0.37 

0.44 

0.54 

5 

4 

0.07 

0.12 

0.17 

0.20 

0.27 

0.33 

0.43. 

6 

5 

0.04 

0.08 

0.12 

0.14 

0.20 

0.25 

0.33 

7 

6 

0.03 

0.06 

0.08 

0.10 

0.14 

0.18 

0.25 

8 

7 

0.02 

0.04 

0.06 

0.06 

0.10 

0.12 

0.18 

9 

8 

0.01 

0.02 

0.04 

0.04 

0.06 

0.08 

0.11 

10 

9 

0.01 

0.01 

0.02 

0.02 

0.03 

0.04 

0.05 

11 

10 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

depend  upon  the  length  of  the  grade  and  upon  the  frequency  with 
which  it  occurs.  If  the  grade  is  only  a  few  hundred  feet  long,  it 
will  probably  be  safe  to  assume  a  pull  equal  to  one  fourth  of  the 
weight  of  the  horse ;  but  this  value  should  be  assumed  only  for  the 


lDministratiox.  35 


maximum  grade,  since  such  pulling  is  too  exhausting  for  continuous 
work. 

Table  11,  page  34,  presents  the  same  data  as  Table  10,  but  in  a 
slightly  different  form. 

42.  The  maximum  load  which  a  horse  can  draw  upon  any  roadr 
particularly  upon  the  steepest  grade,  is  jiot,  Jiowever,  necessarily 
proportional  to  the  rate  of  grade  and  to  the  resistance,  since  the 
pull  that  a  horse  can  exert  depends  upon  the  foothold.  Owing 
to  the  danger  of  slipping  on  steep  grades,  particularly  when  the 
road  is  wet  or  icy,  it  is  not  customary  to  lay  sheet  asphalt  on 
grades  of  more  than  4  per  cent,  or  ordinary  stone  blocks  on  more 
than  10  per  cent.  On  steeper  grades,  special  forms  of  stone  blocks 
are  sometimes  employed  to  increase  the  tractive  power  by  affording 
better  foothold  for  the  horses. 

43.  Road  Administration.  Up  to  the  present  time,  with  but 
few  exceptions,  the  management  of  roads  has  rested  upon  local 
authorities,  either  those  of  townships  or  counties.  In  those  cases 
in  which  the  administration  of  road  affairs  is  nominally  in  the  hands 
of  the  county  authorities,  nothing  has  usually  been  done  except  to 
divide  the  county  into  road  districts  and  virtually  transfer  all 
authority  to  local  officials  appointed  for  that  purpose.  Apparently 
it  is  impossible  to  secure  either  good  roads  or  an  efficient  road  ad- 
ministration by  the  action  of  officials  who  have  only  local  authority, 
and  who  are  necessarily  swayed  by  purely  local,  if  not  individual, 
interests.  This  is  not  peculiar  to  America,  since  great  difficulties 
have  always  been  encountered  in  maintaining  a  system  of  public 
highways  by  any  locally  governed  community. 

The  fundamental  difficulty  is  that  the  small  administrative  unit 
'makes  it  impossible  to  secure  efficient  supervision,  since  the  time 
necessarily  required  in  road  administration  is  but  an  incident 
among  private  or  official  duties.  Another  difficulty  is  that  the 
official  is  usually  elected  for  political  reasons,  rather  than  for  his 
ability  in  matters  relating  to  the  roads.  A  further  difficulty  is  that 
the  tenure  of  office  is  short,  and  successive  officials  have  conflicting 
views  as  to  road  administration  and  road  improvement. 

Another  objection  to  the  small  administrative  unit  is  the  im- 
probability of  the  district's  having  suitable  machinery  in  sufficient 
quantity  to  effectively  and  economically  care  for  the  roads.    At 


36  ROAD    ECONOMICS.  [CHAP.   I. 

present  a  large  amount  of  time  is  wasted  in  transferring  machinery 
from  one  locality  to  another. 

44.  Classification  of  Roads.  As  a  remedy  for  present  evils,  it 
has  frequently  been  urged  that  the  roads  should  be  classified,  ac- 
cording to  their  importance,  into  state,  county,  and  township  roads, 
or  into  county,  township  and  neighborhood  roads,  the  roads  of  each 
class  to  be  under  a  corresponding  administrative  board.  The  possi- 
bilities and  need  of  this  classification  vary  greatly  with  the  topography 
of  a  locality.  For  example,  in  a  prairie  country  one  road  is  nearly 
as  good  as  another,  the  market  places  on  the  railroads  are  nearly 
■uniformly  distributed,  and  all  of  the  roads  have  substantially  equal 
traffic;  while  in  a  broken  country  the  railroads  are  in  the  valleys, 
and  a  wagon  road  in  a  valley  may  carry  the  traffic  for  a  very  large 
outlying  area.  The  proposed  classification  has  never  been  practi- 
cally tried  in  this  country  except  perhaps  in  the  cases  where  state 
aid  is  granted — :as  will  be  considered  presently  (see  §  54).  The 
proposed  change  promises  some  advantages,  but  it  is  by  no  means 
proved  that  the  difficulties  of  administration  would  be  lessened  or 
that  the  quality  of  the  roads  would  be  improved. 

In  some  of  the  older  countries  of  Europe,  the  public  highways 
are  classified  in  a  manner  similar  to  that  referred  to  above,  and 
the  work  of  administration  seems  to  be  reasonably  effective;  but 
success  in  Europe  does  not  guarantee  equal  success  in  America 
with  its  different  social,  political,  and  industrial  conditions.*  There 
is  also  an  important  difference  between  our  own  and  European 
countries  as  to  the  abundance  and  distribution  of  road-building 
material  (§  300),  and  also  as  to  the  length  of  roads  proportional  to 
area  and  population. f 

To  a  great  extent,  the  nations  of  Europe  which  are  noted  for 
their  improved  highways  were  experienced  in  road  building  and 
administration  before  the  advent  of  railroads;  and  consequently  a 
large  proportion  of  the  wagon  roads  are  permanently  hard  roads — 
either  broken  stone  or  stone  block.  On  the  other  hand,  the  develop- 
ment of  America  has  taken  place  to  a  large  degree  since  the  intro- 

*  For  an  outline  of  the  systems  of  road  administration  in  the  several  American 
states  and  in  the  countries  of  Europe,  see  page  14-37  of  Annual  Report  of  the  Depart- 
ment of  Highways  of  the  State  of  California  for  1900. 

•)■  See  an  article  by  the  author  in  Proc.  111.  Soc.  of  Engineers  for  1902,  p.  144-48. 


ROAD    ADMINISTRATION.  37 

duction  of  railroads,  the  railroad  in  many  cases  preceding  the  coming 
of  the  population;  and  consequently  the  railroad  has  made  unneces- 
sary national  or  state  wagon  roads.  A  large  proportion  of  the 
wagon  roads  of  America  are  purely  local,  i.  e.,  run  from  the  farm  to 
the  railroad  town,  and  only  those  near  the  large  cities  have  more 
than  local  importance;  and  hence  a  large  proportion  of  American 
roads  have  only  an  earth  surface,  and  do  not  require  as  close  watch- 
ing nor  as  much  care  as  the  more  expensive  European  roads  with 
their  greater  traffic.  Ordinarily,  in  America  the  amount  of  money 
expended  per  mile  of  road  is  so  small  that  any  adequate  supervision 
by  a  county  or  state  official  would  probably  add  disproportionately 
to  the  expense  (see  §  51). 

Although  in  America  there  are  no  roads  of  state  or  national  im- 
portance as  lines  of  communication,  yet  as  factors  in  the  general 
welfare  of  the  people  wagon  roads  are  of  general  interest  and  con- 
cern to  both  the  state  and  the  nation. 

45.  Education  vs.  Legislation.  Unquestionably  the  prevailing 
American  system  is  not  perfect,  but  a  practical  solution  of  the  prob- 
lem— one  that  will  meet  all  the  conditions — will  be  found  difficult 
of  attainment.  It  is  easy  to  criticise  existing  evils,  to  point  out 
unerringly  the  incongruities  of  the  diversified  provisions  of  the 
statute  books  relative  to  roads,  and  to  join  in  a  general  demand  for 
reform.  Apparently  the  greatest  hope  for  an  improvement  in  the 
public  roads  and  in  road  administration,  is  in  calling  attention  to 
the  defects  in  the  present  methods  and  in  offering  suggestions  for 
their  improvement.  It  is  better  to  try  to  grow  into  an  improved 
system  of  road  management  by  adopting  first  that  which  is  most 
essential  or  the  easiest  to  obtain — then  taking  other  steps  as  the 
people  become  educated  to  the  importance  of  efficient  road  admin- 
istration,— rather  than  to  attempt  a  revolution  in  road  affairs  by 
legislation.  Our  efficient  railways  were  not  created  in  a  day,  but 
are  a  natural  development.  A  cheap  line  was  first  constructed, 
and  this  was  gradually  perfected  as  the  necessary  money  could  be 
obtained  and  as  the  conditions  were  better  understood  and  as  the 
requisite  skill  was  developed. 

It  is  probably  wiser  to  direct  attention  to  the  defects  in  the 
present  roads  and  to  the  inefficient  administration  of  the  present 
laws,  than  to  attempt  to  secure  improved  roads  and  effective  admin- 


38  ROAD    ECONOMICS.  [CHAP.  I. 

istration  by  enacting  new  laws.  As  illustrating  the  improbability 
of  securing  improved  road  administration  by  legal  enactment  un- 
supported by  public  sentiment,  it  may  be  mentioned  that  at  one 
time  in  Illinois  a  state  law  wisely  required  that  the  major  part  of 
the  labor  road-tax  should  be  paid  in  May  and  June, — when  the 
roads  most  need  attention  and  when  the  labor  would  be  most 
effective; — but  the  law  was  practically  a  dead  letter,  since  in  thcs3 
months  the  farmers  were  more  interested  in  putting  in  their  crops. 

For  a  valuable  discussion  of  European  and  American  systems 
of  road  administration,  see  pages  88-108  and  176-185  of  Shaler's 
American  Highways,  New  York,  1896. 

46.  The  following  extracts  from  a  farmer's  bulletin  by  the 
author,  suggests  some  details  as  to  the  methods  to  be  employed  in 
securing  an  effective  administration  of  road  affairs.  These  sug- 
gestions were  made  with  direct  reference  to  earth  roads — which 
constitute  perhaps  90  or  95  per  cent  of  the  highways  of  this  country, 
— but  they  are  hardly  less  applicable  to  any  system  of  roads. 

"1.  It  is  believed  that  material  improvement  can  be  attained 
by  paying  more  attention  to  the  office  of  Highway  Commissioner 
and  Pathmaster.  Elect  only  the  very  best  men,  without  regard  to 
party;  men  who  have  judgment  in  business  affairs,  who  have  ideas 
on  road  making  and  maintenance,  who  have  skill  in  directing  the 
labor  of  others,  and  who  will  give  to  their  official  duties  their  best 
endeavor.  If  they  do  reasonably  well  and  are  continually  seeking 
to  increase  their  road  knowledge  and  to  improve  the  roads  under 
their  care,  continue  them  in  office.  If  not,  try  again  to  find  some 
one  who  will  do  these  things.  Dignify  the  office  by  every  means 
possible. 

"2.  In  private  conversation  and  in  public  meeting,  discuss  ways 
and  means  of  improving  the  earth  roads.  Organize  for  the  purpose 
of  creating  interest  in  common  earth  roads.  As  soon  as  possible 
adopt  rules  for  the  guidance  of  the  road  officials,  and  then  let  each 
tax  payer  note  whether  these  rules  are  obeyed.  Do  not  fail  to 
give  due  credit  if  they  are ;  and  if  they  are  not,  do  not  shrink  from 
entering  a  respectful  protest.  Unless  the  earth  roads  are  main- 
tained in  reasonably  good  condition,  it  is  folly  even  to  talk  of  con- 
structing high-priced  broken-stone  roads. 

"3.  Divide  the  roads  up  and  allot  definite  sections  to  particular 


KOAD    TAXES.  39 


farmers,  and  publish  these  allotments,  which  fixes  responsibility.  As 
far  as  possible  require  each  man  to  care  for  the  road  nearest  home  and 
which  he  travels  most.  By  private  conversation  and  public  meet- 
ing seek  to  stimulate  pride  in  road  making  and  maintenance,  and 
try  to  secure  the  effect  of  competition  in  road  work.  Possibly  have 
annual  inspections,  and  award  prizes  and  diplomas.  Railroads  find 
annual  inspections  and  nominal  cash  prizes  and  diplomas  exceed- 
ingly effective.  France  has  a  system  of'  gratuities  for  excellence 
in  road  work. 

"4.  Permanently  hard  roads  are  very  desirable  if  their  cost  is 
not  too  great;  but  remember  that  high-class  stone  or  gravel  roads 
are  not  feasible  unless  the  road-bed  is  thoroughly  underdrained, 
and  unless  the  subgrade  is  adequately  crowned,  and  unless  the 
public  understands  the  superiority  of  perpetual  maintenance  over 
annual  repairs,  and  unless  the  road  officials  are  intelligent,  energetic, 
and  conscientious.  Fortunately  these  things  are  the  very  best 
investments  for  earth  roads,  and  good  earth  roads  are  the  very 
best  preparation  for  good  gravel  or  broken-stone  roads. 

"5.  Do  not  overlook  the  fact  that  the  interest  in  good  roads 
should  have  a  broader  foundation  than  mere  commercial  needs. 
Comfortable  and  easy  communication  between  the  members  of  a 
rural  community  and  also  between  rural  and  urban  inhabitants  is 
of  great  importance  in  the  social  and  educational  development  of 
a  community." 

47.  ROAD  TAXES.  How  shall  the  expense  of  constructing  and 
maintaining  roads  be  distributed?  This  question  has  been  answered 
in  various  ways  in  different  parts  of  this  country  and  in  different 
countries  of  Europe.  There  are  three  forms  of  road  taxes;  viz.: 
(1)  a  tax  upon  the  traveler,  (2)  a  capitation  tax,  and  (3)  a  prop- 
erty tax.  The  first  leads  to  toll  roads ;  and  the  second  is  usually 
called  a  poll-tax. 

48.  Toll  Roads.  These  are  conducted  on  the  theory  that  the 
travelers  over  a  road  are  the  recipients  of  its  benefits  and  should 
pay  for  its  support.  Toll  roads  are  justifiable  only  in  a  new  country 
where  the  amount  of  taxable  property  is  small,  and  where  for  long 
stretches  of  territority  there  are  few  inhabitants,  since  they  induce 
the  investment  of  capital  that  possibly  the  pioneer  or  the  new 
community  could  not  afford;  and  even  under  these  conditions  they 


40  ROAD    ECONOMICS.  [CHAP.   I. 

are  practicable  only  where  there  is  considerable  traffic.  In  early 
times  the  government  collected  the  toll  and  used  it  for  the  main- 
taining and  extension  of  the  road ;  but  in  recent  times  toll  roads  are 
usually  in  the  hands  of  private  capitalists.         -v-  «u- 

Toll  roads  are  objectionable  owing  to  the  proportionally  great 
expense  of  collecting  the  revenue,  and  owing  to  the  fact  that  they 
are  managed  solely  with  reference  to  securing  returns  upon  the 
capital  invested  and  without  regard  to  the  interests  of  the  public. 
The  only  remedy  for  the  evils  of  the  system  is  for  the  public  to 
support  the  roads.  Roads  are  an  indispensable  public  convenience 
— a  benefit  to  every  citizen,  whether  a  direct  user  of  the  road  or 
not, — and  consequently  should  be  maintained  by  a  universal  tax. 
At  present  the  toll  system  is  regarded  as  unwise  for  both  economic 
and  political  reasons;  and  toll  roads  have  almost  entirely  been 
abolished  both  in  this  country  and  in  Europe. 

49.  Poll-tax.  Notwithstanding  the  fact  that  most  writers  on 
political  economy  consider  a  capitation  tax  an  undesirable  form 
of  taxation,  nearly  all  of  the  states  levy  a  poll-tax  for  road  purposes. 
Apparently  it  is  the  only  capitation  tax.  It  is  not  wise  to  occupy 
space  here  to  inquire  into  either  the  wisdom  or  reason  for  this  form 
of  road  taxes. 

Almost  universally  the  law  permits  the  payment  of  the  poll 
road-tax  in  money  or  labor,  and  it  is  usually  paid  in  labor.  In  the 
poorer  and  less  populous  states,  this  tax  is  nearly  the  sole  support 
of  the  road  system.  In  many  states  there  are  numerous  exemp- 
tions, and  in  all  states  the  tax  is  difficult  to  collect,  and  consequently 
the  poll-tax  is  an  unimportant  element  in  road  construction  and 
maintenance. 

50.  Property  Tax.  There  are  three  forms  of  the  property  road 
tax:  the  special  assessment,  the  direct  tax,  and  the  general  tax. 

In  many  states  when  any  considerable  road  improvement  is 
contemplated,  part  or  all  of  the  cost  of  the  same  is  laid  as  a  special 
tax  or  assessment  on  all  real  estate  within  some  certain  distance  of 
the  improvement.  In  Indiana  at  one  time,  this  distance  was  two 
miles ;  and  in  Wisconsin,  three.  Ordinarily  this  tax  is  not  uniform 
over  the  included  area,  but  is  graded  according  to  the  supposed 
benefits.     This  tax  is  usually  payable  in  money. 

In  most  of  the  states,  the  territory  is  divided  into  small  units, 


ROAD    TAXES.  41 


called  road  districts,  and  a  uniform  road  tax  is  laid  upon  all  prop- 
erty within  the  district.  Usually  this  tax  may  be  paid  in  either 
money  or  labor;  and  when  so  permitted,  is  usually  paid  in  labor. 

In  most  states  there  is  also  a  general  property  tax  for  road  and 
bridge  purposes,  which  must  be  paid  in  money. 

In  poorer  communities  the  roads  are  cared  for  principally  by 
the  district  road  tax,  which  is  usually  paid  in  labor;  but  in  wealthier 
communities  the  general  property  road  and  bridge  tax  (cash  tax) 
is  greater  than  the  district  road  tax  (labor  tax). 

51.  Cost  of  Roads.  There  are  almost  no  definite  data  as  to  the 
amount  expended  for  road  purposes.  The  following  are  all  that 
can  be  found. 

In  Massachusetts  the  average  annual  expenditures  of  the 
towns  (townships),  exclusive  of  the  cities,  for  highways,  exclusive 
of  the  bridges,  for  the  years  1889,  1890,  1891,  were  as  follows:* 
$22.17  per  mile  of  road,  the  range  for  the  different  towns  (townships) 
being  from  $2.20  to  $191.00;  $50.72  per  square  mile;  or  $0.46  per 
capita,  the  range  being  $0.06  to  $4.68.  In  20  per  cent  of  the 
townships,  the  average  annual  expenditure  was  $5.40  per  mile;  in 
the  next  27  per  cent,  $9.60;  and  in  the  next  18  per  cent,  $12.73. 
These  were  the  expenditures  before  the  inauguration  of  state  aid 
(§  54).  It  is  interesting  to  note  that  the  per  cent  of  the  total  tax- 
receipts  spent  upon  the  roads  is  practically  the  same  in  the  rural 
districts  as  in  the  cities,  being  13.7  per  cent  in  the  former  and  11.2 
in  the  latter. 

"In  1893  the  road  expenditures  in  New  Jersey  were  $778,470.82, 
or  $43.24  per  mile  (about  one  fifth  being  for  new  broken-stone  roads) ; 
in  New  York  about  $2,500,000,  or  about  $30  per  mile."t 

In  Vermont  in  1893  the  .  expenditures  for  road  purposes,  includ- 
ing culverts  but  excluding  bridges,  in  country  and  cities,  were 
$30.22  per  mile;  and  in  1894,  $32,134 

In  Connecticut  in  1889  the  expenditures  for  roads  in  the  different 
townships  averaged  $34.04  per  mile,  the  maximum  being  $201.22 
and  the  minimum  $7.91.§ 

♦Report  of  Massachusetts  Highway  Commission  for  1893,  p.  218-31. 

f  Gen.  Francis  V.  Greene,  before  the  students  of  Union  College,  Schenectady, 
N.  Y.,  reprinted  in  Bulletin  No.  17  of  the  Road  Inquiry  Office  of  the  U.  S.  Depart- 
ment of  Agriculture. 

|  Report  of  Highway  Commission,  1894,  p.  77-91;  1896,  p.  61-74. 

§  Proc.  Conn.  Assoc,  of  Civil  Engineers  and  Surveyors,  1890  and  1891,  p.  107-110. 


42  ROAD    ECONOMICS.  [CHAP.   I. 

"The  public  roads  of  Washington  County,  Md.,  have  cost  $20 
per  year."  * 

In  Champaign  county,  111.,  according  to  statistics  collected  by 
the  author,!  the  expenditures  for  road  purposes,  outside  of  incor- 
porated cities  and  villages,  in  1900  were  $34.86  (for  details  see 
§  220). 

52.  Labor  vs.  Money  Tax.  In  all  the  states  except  five,  the 
labor  tax  is  regularly  employed. X  ^n  one  state  at  least  (Illinois) 
the  road  tax  may  be  collected  in  money  or  labor  as  the  township 
by  election  may  decide, — and  a  large  majority  of  the  towns  vote 
in  favor  of  the  labor  system.  The  labor-tax  system  was  inherited 
from  England,  and  is  a  survival  of  the  feudal  method  of  requiring 
all  able-bodied  men  to  render  public  service.  England  and  France 
have  a.  labor  road-tax,  but  upon  a  much  less  extensive  scale  than 
has  this  country. 

The  roads  and  streets  of  the  cities,  towns,  and  villages  are  usually 
under  the  control  of  the  municipalities,  in  which  as  a  rule  the  labor 
tax  does  not  exist;  therefore  the  labor-tax  system  applies  chiefly, 
if  not  wholly,  to  rural  communities.  Further,  since  a  very  large 
proportion  of  the  roads  are  of  earth,  the  labor-tax  system  is  usually 
applied  to  the  construction  and  care  of  earth  roads. 

It  is  common  to  assume  that  the  labor-tax  system  is  all  wrong, 
and  that  its  evils  would  be  escaped  by  paying  road  taxes  in  money. 
The  labor  tax  has  inherent  disadvantages,  but  many  of  the  defects 
charged  to  it  belong  rather  to  defective  administration  and  to  the 
system  that  leaves  the  control  of  the  public  highways  to  a  small 
locally  governed  community.  Public  work  is  seldom  as  economi- 
cally done  as  private  work.^^K5^ 

The  objections  to  the  labor-tax  system  are:  1.  The  labor  is  in- 
different and  inefficient.  2.  It  is  impossible  to  get  the  work  done 
at  the  most  suitable  time.  3.  The  system  allows  no  selection  of 
the  laborer.     All  of  these  are  important  considerations. 

The  reply  to  the  above  objections  is  usually  about  as  follows: 
1.  The  farmer  is  willing  to  pay  more  in  labor  than  in  money,  which 
compensates  in  part,  at  least,  for  the  objections  to  the  labor-tax 
system.     This  preference  is  not  peculiar  to  the  American  farmer. 

♦Trans.  Amer.  Soc.  of  C.  E.,  Vol.  28,  p.  111. 

fProc.  Illinois  Society  of  Engineers  and  Surveyors,  1901,  p.  48-52. 

%  Road  Legislation  for  the  American  State,  Jeremiah  W.  Jenks,  Baltimore,  1889. 


KOAD   TAXES.  43 


In  France,  if  the  road  tax  is  paid  in  money,  a  reduction  of  40  to  50 
per  cent  is  made;  but  still  60  per  cent  of  the  people  prefer  to  pay  in 
labor.*  Farmers  not  infrequently  give  more  both  in  labor  and 
money  than  is  exacted  as  road  taxes,  because  they  are  interested 
in  better  roads.  2.  In  many  rural  communities  it  is  impossible  to 
secure  any  one  to  do  road  work  at  reasonable  wages  at  the  most 
suitable  season.  3.  If  the  tax  were  paid  in  money,  there  is  no 
certainty  that  the  labor  would  be  any  more  efficient.  Streets  are 
maintained  under  the  cash-tax  system,  but  the  labor  is  not  ideally 
efficient.  The  authority  that  virtually  wastes  the  labor  tax  will 
probably  also  waste  the  cash  tax. 

53.  The  labor  tax  is  not  necessarily  the  cause  of  inferior  roads, 
nor  the  cash-tax  system  in  itself  the  cause  of  improved  roads. 
Townships  under  the  labor-tax  system  often  have  better  roads  than 
adjoining  townships  under  the  cash-tax  system.  The  one  thing 
absolutely  necessary  for  successful  road  management  is  effective 
supervision  of  the  work.  Without  it  neither  system  will  accom- 
plish much,  and  with  it  either  system  will  do  reasonably  well. 

Many  townships  have  changed  from  the  labor-tax  system  to  the 
cash-tax  system  with  a  marked  improvement  in  the  condition  of  the 
roads — due  chiefly,  if  not  wholly,  to  better  administration.  For  in 
many  of  these  cases  the  so-called  cash-tax  system  is  practically 
only  a  change  in  the  method  of  administering  the  labor-tax  system, 
since  farmers  desiring  to  do  so  are  given  an  opportunity  to  work  out 
their  road  taxes  under  the  cash  system.  Under  the  labor-tax 
system  those  working  upon  the  roads  receive  credit  on  their  road 
taxes,  while  in  the  so-called  cash  system  the  laborer  receives  an 
order  which  is  accepted  as  cash  in  paying  taxes.  In  these  cases  the 
public  sentiment  that  demanded  road  improvement  secured  the 
change  from  the  labor  tax  to  the  cash  tax;  and,  consciously  or  un- 
consciously, also  secured  a  more  efficient  road  administration. 

The  labor-tax  system  is  more  objectionable  with  broken-stone 
roads  than  with  earth  ones,  since  the  construction  of  the  former  is 
more  difficult  and  tneir  maintenance  requires  intimate  knowledge 
and  constant  attendance,  and  also  since  the  former  are  built  only 
where  there  is  more  travel  and  where  the  labor  of  maintenance  is 

*  French  Roads,  their  Administration,  Construction,  and  Maintenance,  Prof. 
Frank  H.  Neff,  Jour.  Associated  Eng'g  Societies,  Vol.  11,  p.  1-16. 


44  ROAD   ECONOMICS.  [CHAP.   I. 

greater.     This  subject  will  be  considered  incidentally  under  Mainte- 
nance in  the  chapters  on  earth,  gravel,  and  broken-stone  roads. 

54.  State  Aid.  In  1891  New  Jersey  inaugurated  a  new  depar- 
ture in  road  administration  in  America — that  of  state  aid  in  road 
construction.  A  state  law  provides  that  on  „he  petition  of  a  major- 
ity of  the  adjacent  property  owners,  a  gravel  or  broken-stone  road 
shall  be  built,  under  the  direction  of  the  State  Highway  Commis- 
sioner, 33J  per  cent  of  the  expense  to  be  borne  by  the  state,  10  per 
cent  by  the  abutting  property,  and  56 J  per  cent  by  the  county.  The 
maintenance  of  the  improved  road  is  in  the  hands  of  the  county 
officials. 

In  1893  Massachusetts  inaugurated  a  somewhat  similar  system 
of  state  aid  for  road  improvement.  Under  the  Massachusetts  law 
the  road  improvement  may  be  petitioned  for  by  the  town,  county^ 
or  city  authorities;  and  the  state  bears  75  per  cent  of  the  expense, 
and  the  county  25  per  cent.  Notice  that  no  part  of  the  expense  of 
the  improvement  is  laid  directly  upon  either  the  abutting  property 
or  the  township.  This  is  a  concession  to  the  poorer  communities, 
which  are  'frequently  most  in  need  of  improved  highways.  The 
maintenance  of  the  roads  is  in  the  hands  of  the  township  authorities, 
with  a  general  oversight  by  the  State  Commission. 

In  1895  Connecticut  inaugurated  a  similar  system  of  state  aid. 
The  distribution  of  the  expense  has  changed  from  time  to  time:  in 
1895  one  third  each  by  state,  county,  and  town;  in  1897,  one  half 
each*  by  state  and  town;  and  in  1899,  one  third  by  small  towns  and 
two  thirds  by  large  towns,  the  remainder  in  each  case  by  the  state. 

In  1898  New  York  adopted  a  state-aid  system,  whereby  the  state 
pays  50  per  cent,  the  county  35  per  cent,  and  the  town  15  per  cent. 
The  practice  in  New  York  differs  from  that  in  the  other  states  in 
that  the  state-aid  fund  may  be  used  for  the  improvement  of  earth 
roads. 

55.  The  principle  of  state  aid  is  defended  on  the  ground  that 
(1)  it  secures  centralized  control,  (2)  makes  the  wealth  of  the  city 
bear  part  of  the  expense  of  maintaining  the  country  roads,  and  (3) 
compels  the  railroads  and  other  state-wide  corporations  to  bear 
part  of  the  expense  of  local  improvements. 

In  Europe  nearly  all  countries  give  national  aid  in  some  form 
for  building  roads. 


SUPPLEMENTAL  NOTE. 

COST  OF   WAGON  TRANSPORTATION. 

On  pages  11-21  is  a  discussion  of  some  statistics  concerning 
the  cost  of  transportation  on  wagon  roads  collected  by  the  Road 
Inquiry  Office  of  the  U.  S.  Department  of  Agriculture  and  pub- 
lished under  date  of  April  4,  1896.  Under  date  of  February  28, 
1907,  the  Bureau  of  Statistics  of  the  same  Department  published 
Bulletin  No.  49  —  Cost  of  Hauling  Crops  from  Farm  to  Shipping 
Points.*  It  is  proposed  to  briefly  compare  the  results  of  these 
two  investigations,  and  also  to  study  the  reliability  of  the  con- 
clusions of  the  second  bulletin. 

In  the  last  investigation  the  cost  of  hauling  the  twelve  leading 
farm  products  from  the  farm  to  the  shipping  point  during  the 
crop  year  of  1905-06  is  said  to  be  $84,684,000;  whereas  in. the 
first  investigation  the  cost  in  1895  of  hauling  all  crops  from  the 
farm  to  the  market  was  said  to  be  70  per  cent  of  $946,314,666  or 
$652,000,000.  Notice  that  the  cost  according  to  the  later  and 
more  elaborate  investigation  is  only  about  one  eighth  of  that  by 
the  former  investigation,  notwithstanding  the  fact  that  the 
weight  of  the  seven  leading  crops  was  almost  exactly  50  per 
cent  greater  in  1905  than  in  1895  ;  in  other  words,  on  the  face 
of  the  returns,  the  result  in  the  first  bulletin  is  about  sixteen 
times  too  great.  Besides,  the  result  of  the  second  investigation 
is  too  large,  on  account  of  four  serious  errors;  and  hence  the 
first  result  is  still  more  too  great. 

1.  The  average  distance  of  haul  is  too  great.  The  question 
was:  "What  is  the  greatest  distances  of  haul  by  any  consider- 
able number  of  farmers?  "  In  deducing  the  results  it  was  assumed 
that  the  answer  was  the  radius  circumscribing  the  area  tributary 
to  the  particular  shipping  point.  This  assumption  is  seriously 
in  error,  since  produce  may  be  hauled  much  farther  from  one 
direction  than  from  another;  and  therefore  the  tabulated  result 
is  too  great.  The  average  length  of  haul  for  corn  in  Illinois  is 
given  as  5.7  miles;  while  the  actual  distance  is  probably  about 
3.2  miles  (see  §§15-18).     Therefore   the   actual   distance   which 

*  Fully  abstracted  in  Engineering  News,  Vol.  57,  p.  419-20. 
44a 


446  ROADS    AND    PAVEMENTS. 

corn  is  hauled  in  Illinois  is  probably  only  about  60  per  cent  of 
that  stated  in  Bulletin  No.  49;  and  doubtless  the  results  for  other 
products  and  other  states  are  equally  in  error. 

2.  The  average  weight  of  a  load  of  corn  in  Illinois  is  given  at 
2754  lbs.  (1.37  tons).  Judging  by  the  results  in  §  19,  it  is  prob- 
able that  the  actual  load  is  about  2  tons;  and  therefore  we  may 
conclude  that  the  cost  of  transportation  given  in  Bulletin  No.  49 
is  proportionally  too  high,  or  in  other  words,  for  this  reason 
alone  the  actual  cost  is  only  about  68  per  cent  of  that  stated  in 
Bulletin  No.  49. 

3.  The  cost  per  ton-mile,  as  given  in  Bulletin  No.  49,  was  found 
by  asking  the  usual  cost  per  day  of  hiring  team  and  driver.  This 
method  is  wrong,  since  the  cost  to  a  farmer  is  quite  different 
than  that  to  a  professional  teamster,  owing  to  differences  in  the 
conditions  of  service,  in  the  cost  of  rent  and  of  feed,  in  the  cost 
of  driver,  etc.  The  cost  of  a  team  and  driver  in  Illinois  is  given 
at  $2.94  per  day,  which  is  nearly  10  per  cent  higher  than  the 
maximum  given  in  paragraph  1,  §  20.  The  conclusion  of  the 
above  discussion  is  that  the  actual  cost  of  hauling  corn  in 
Illinois  is  only  about  0.60  X  0.67  X  0.90  =  35  per  cent  of  that 
stated  in  Bulletin  No.  46.  According  to  Bulletin  No.  46  the 
cost  of  hauling  corn  to  market  is  equivalent  to  19  cents  per 
ton-mile,  while  the  values  stated  in  §  21  are  only  one  half  to 
one  third  this  amount,  which  roughly  checks  the  above 
discussion. 

4.  The  second  bulletin  finds  the  cost  of  hauling  crops  from 
the  farm  to  the  market  to  be  $72,984,000;  and  then  adds 
$11,700,000  as  the  cost  of  hauling  wheat  to  local  mills  to  be 
ground.  This  allowance  is  altogether  too  great,  since  it  assumes 
that  more  than  one  third  of  the  wheat  not  used  for  seed  is 
ground  at  the  local  mill.  No  data  are  known  by  which  to 
determine  the  amount  of  this  particular  error. 

Correcting  the  above  errors  would  reduce  the  total  of  the 
second  bulletin  to  one  half  or  one  third,  and  make  the  first 
result  thirty  to  fifty  times  too  great.  Unfortunately  the  results 
of  the  first  investigation  are  frequently  used  in  discussions  con- 
cerning road  economics,  and  the  object  of  this  note  is  to  more 
fully  show  their  utter  unreliability. 


CHAPTER   II. 
ROAD  LOCATION. 

56.  ELEMENTS  INVOLVED.  In  general  the  determination  of  the 
best  location  for  a  road  requires  a  study  of  the  topographical  fea- 
tures of  the  region  through  which  the  road  is  to  pass,  and  also  an 
investigation  of  the  nature  and  extent  of  the  traffic  to  be  provided 
for.  Viewed  as  a  question  of  economics,  the  best  location  is  that 
for  which  the  sum  of  the  interest  on  the  cost  of  construction  and  of 
the  annual  cost  of  maintaining  the  road  and  of  conducting  trans- 
portation over  it,  is  a  minimum.  The  location  of  a  wagon  road  is 
not,  however,  entirely  a  question  of  economics,  since  the  location 
should  be  made  with  reference  to  the  convenience  and  comfort, 
and  perhaps  also  to  the  pleasure,  of  those  who  use  it;  and  is  fre- 
quently more  of  a  social  or  political  question  than  one  of  economics. 
Only  the  economic  features  of  location  will  be  considered  here,  and 
they  only  briefly. 

However,  in  locating  a  new  wagon  road,  it  is  well  to  remember 
that  the  location  will  probably  serve  for  many  generations,  and 
perhaps  for  all  time,  as  the  growing  importance  of  the  surrounding 
country  and  the  location  of  buildings  and  of  division  lines  of  the 
land  with  reference  to  the  road  make  it  increasingly  more  difficult 
and  expensive  to  change  the  location.  Thus  the  location  of  a  road 
is  the  field  where  costly  errors  and  permanent  blunders  may  creep 
in  and  forever  fasten  themselves  upon  the  road  and  its  users;  and, 
worst  of  all,  these  errors  become  more  costly  as  the  use  of  the  road 
increases. 

In  most  parts  of  the  United  States,  the  roads  are  in  the  main 
already  located,  and  the  necessity  for  the  location  of  new  ones  does 
not  often  arise;  and  hence  as  a  rule,  the  only  application  of  the 
principles  of  economic  location  will  be  in  the  re-location  of  com- 
paratively short  stretches  of  roads.     The  original  location  may 

45 


46  ROAD   LOCATION.  [CHAP.   II. 

have  been  fit  and  proper  when  the  region  was  new  and  undeveloped, 
but  the  increase  in  the  amount  and  the  change  in  the  character  of 
the  traffic  may  justify  a  very  considerable  change.  There  are  many 
roads  that  could  be  materially  improved  by  a  careful  re-location. 

57.  The  principles  to  be  observed  and  the  methods  to  be  em- 
ployed in  making  the  location  of  a  wagon  road  are  substantially  the 
same  as  those  used  in  the  location  of  a  railroad.  The  method  of 
examining  the  country  and  of  making  surveys  will  not  be  considered 
here,  as  such  subjects  are  elaborately  presented  in  treatises  on  rail- 
road location. 

The  fundamental  principles  applicable  in  locating  a  new  road 
or  in  improving  an  old  one  will  be  briefly  considered;  but  no  hard 
and  fast  rules  can  be  laid  down,  for  each  road  must  be  designed  for 
the  place  it  is  to  occupy  and  the  service  it  is  to  render.  In  the  loca- 
tion of  any  road  there  will  always  be  an  opportunity  to  exercise 
keen  insight  and  good  judgment. 

The  subject  will  be  considered  under  the  four  heads:  distance, 
grades,  curves,  width,  and  placing  the  line. 

58.  DISTANCE.  Other  things  being  equal,  the  shorter  the 
road  the  better,  since  any  unnecessary  length  causes  a  constant 
threefold  waste:  (1)  the  interest  on  the  cost  of  constructing  the 
extra  length;  (2)  the  ever-recurring  cost  of  repairing  it;  and  (3) 
the  time  and  labor  employed  in  traveling  over  it.  However,  the 
advantage  of  straightness,  i.  e.,  of  shortness,  is  usually  greatly  over- 
estimated. The  difference  in  length  between  an  absolutely  straight 
line  and  one  deflecting  a  little  to  one  side  is  not  very  great.  For 
example,  in  Fig.  3,  if  A  B=B  C=  1,000  feet,  and  B  D=  10  feet,  the 

line  A  B  C  is  only  one  tenth  of  a  foot 
longer  than  the  line  A  D  C*  If 
A  B=BC=1  mile,  and  B  D  =  S00 
feet,  the  line  A  B  C  is  only  17  feet 
longer  than  ADC.  "If  a  road  be- 
tween two  places  ten  miles  apart  were  made  to  curve  so  that  the 
eye  could  nowhere  see  more  than  a  quarter  of  a  mile  of  it  at  once, 

*  The  difference  between  A  D  and  A  B  is  given  with  sufficient  accuracy  by  the 
approximate  formula  :AB-AD  =  2AI)  =  ^~~.  For  the  demonstration  of  this 
formula,  see  the  author's  Engineer's  Surveying  Instruments,  p.  16. 


DISTANCE.  47 


its  length  would  exceed  that  of  a  perfectly  straight  road  between 
the  same  points  by  only  about  one  hundred  and  fifty  yards."  * 

One  of  the  most  common  defects  of  ordinary  country  roads  is 
that  distance  has  been  saved  by  a  disregard  of  the  desirability  of 
easy  gradients.  The  curving  road  around  a  hill  may  often  be  no 
longer  than  the  straight  one  over  it;  for  the  latter  is  straight  only 
with  reference  to  the  horizontal  plane,  but  curved  as  to  the  vertical 
plane,  while  the  former  is  curved  as  to  the  horizontal  plane,  but 
straight  as  to  the  vertical  plane.  Both  lines  curve,  and  the  one 
passing  over  the  hill  is  called  straight  only  because  its  vertical 
curvature  is  less  apparent  to  the  eye. 

59.  Value  of  Saving  Distance.  Theoretically  the  value  of  a 
difference  in  length  may  be  computed  by  determining  (1)  the 
amount  of  traffic,  (2)  the  cost  per  ton-mile,  and  (3)  the  total  cost 
of  conducting  the  traffic;  and  then  assuming  that  the  value  of  any 
difference  of  length  is  to  the  total  cost  of  transportation  as  the 
difference  of  the  length  is  to  the  total  length.  If  the  annual  cost  of 
conducting  transportation  over  a  given  road  is  known,  then  this 
cost  divided  by  the  length  of  the  road  gives  the  annual  interest  upon 
the  sum  that  may  be  reasonably  expended  in  shortening  the  road 
1  mile,  i.  e.,  the  value  of  a  saving  of  a  mile  of  distance;  and  of  course 
dividing  this  sum  by  the  number  of  feet  in  a  mile  will  give  the  value 
of  saving  1  foot  of  distance. 

Unfortunately  it  is  not  possible  to  determine  the  amount  of 
traffic  with  any  considerable  degree  of  accuracy.  At  some  railroad 
stations  the  sole  freight  shipped  out  is  agricultural  produce,  in 
which  case  the  traffic  over  any  particular  wagon  road  can  be  approx- 
imated by  distributing  the  shipments  according  to  the  contributing 
area.  The  average  load  can  be  determined  with  sufficient  accuracy 
by  consulting  the  records  of  the  grain  dealers  In  addition  to  the 
above,  which  may  be  called  the  heavy  freight  traffic,  there  is  a 
considerable  amount  of  light  freight  and  passenger  traffic  which 
would  be  benefited  by  a  saving  of  distance. 

For  the  sake  of  working  out  an  example,  it  will  be  assumed  that 
the  cost  of  transportation  is  10  cents  per  ton-mile.  This  cost  is 
made  up  of  the  cost  of  loading  and  unloading,  of  driving,  of  feed, 

*  Gillespie's  Manual  of  Road  Making,  p.  27.    New  York,  1847. 


48  KOAD    LOCATION.  [CHAP.   II. 

and  of  wear  aid  tear  of  horses,  wagon,  and  harness.  The  cost  of 
loading  and  unloading  is  independent  of  distance.  The  cost  of 
driving  nominally  varies  as  the  time,  i.  e.,  as  the  distance  (see  third 
paragraph  of  §  60).  The  cost  of  feed  and  of  wear  and  tear  varies 
as  the  distance.  It  is  impossible  to  assign  reliable  values  to  these 
several  factors  of  the  cost,  but  it  is  certain  that  only  part  of  the  cost 
of  transportation  varies  as  the  distance;  and  for  the  sake  of  com- 
pleting the  illustration,  it  will  be  assumed  that  8  cents  per  ton-mile 
varies  as  the  distance.  This  sum  multiplied  by  the  number  of  tons 
passing  over  the  road  in  a  year  will  give  the  sum  that  may  be  spent 
annually  to  secure  a  saving  of  1  mile  of  distance. 

For  example,  a  road  leading  to  a  certain  village  was  originally 
laid  out  on  the  east  and  north  sides  of  a  quarter-section,  but  on 
account  of  low  ground  on  the  northeast  corner  another  road  was 
opened  on  the  south  and  west  sides.  The" quarter-section  was  one 
large  field.  How  much  expense  would  the  traffic  justify  in  order  to 
secure  a  road  diagonally  through  the  quarter-section?  The  heavy 
freight  traffic  was  approximately  3,000  loads  of  1  ton  each  per  annum. 
The  annual  value  of  saving  1  mile  would  then  be  8  cents  X  3,000  = 
$240.  The  saving  in  distance  by  going  through  the  quarter-sec- 
tion is  0.29  mile;  and  the  annual  value  of  saving  this  distance  is 
$240X0.29 -=$69.60.  The  diagonal  road  occupies  2 J  acres  less  land 
than  the  longer  one;  and  as  the  land  rented  for  $3  per  acre,  this 
adds  $3  X  2 J  =  $7  per  annum  to  the  value  of  the  diagonal  road.  The 
annual  saving  from  these  two  items  is  then  $69.60 +  $7.00  =  $76.60. 
This  is  the  interest  at  5  per  cent  on  $1,532,  which  sum,  according  to 
the  above  computations,  could  be  borrowed,  and  used  to  secure  this 
improvement,  and  the  community  be  no  worse  off  financially. 

In  addition,  there  would  be  some  advantage  to  the  light  freight 
and  passenger  traffic  by  shortening  the  road,  but  it  is  difficult,  if  not 
impossible,  to  estimate  this  saving;  and  as  the  benefit  per  trip 
would  probably  be  less  than  for  the  heavy  freight  traffic,  it  was 
neglected.  There  would  be  a  slight  saving  in  the  cost  of  mainte- 
nance of  the  shorter  road,  as  in  this  case  the  soil  and  drainage  was 
as  good  on  one  line  as  on  the  other.  Further,  there  would  be  some 
saving  on  the  return  trip  by  the  shorter  road.  On  the  other  hand, 
it  is  probable  that  the  smaller  number  of  acres  required  for  the 
diagonal  road  would  cost  at  least  as  much  as  for  the  road  around 


DISTANCE.  49 


the  quarter-section,  owing  to  the  farmers'  justifiable  dislike  for  non- 
rectangular  fields,  and  because  the  diagonal  road  would  divide  the 
quarter-section. 

60.  There  are  several  matters  that  materially  affect  the  relia- 
bility of  the  method  of  the  above  investigation.  In  the  first  place, 
the  cost  of  transportation  can  not  be  known  with  any  degree  of 
reliability.  The  farmers  concerned  would  stoutly  contend  that  the 
price  assumed  above  is  much  too  great  (see  §  20-21) ;  while  freighters 
would  claim  that  the  value  assumed  was  too  low  (see  §  4-7). 

In  the  second  place,  not  all  of  the  computed  annual  saving  is 
available  for  making  the  improvement,  since  some  of  it  should  be 
set  aside  to  form  a  sinking  fund  to  be  used  ultimately  in  extinguish- 
ing the  debt.  It  is  not  the  part  of  wisdom  to  extend  the  debt  very 
far  into  the  future,  since  the  conditions  may  materially  change. 
For  example,  a  new  railroad  may  divert  the  traffic  from  this  par- 
ticular road,  or  improvements  in  the  condition  of  the  surface  of  the 
road  may  decrease  the  cost  of  transportation, — either  of  which 
would  decrease  the  value  of  the  proposed  improvement.  Of  course, 
certain  contingencies  may  increase  the  traffic  and  thereby  add  to 
the  value  of  the  improvement;  but  it  is  not  wise  to  incur  a  definite 
debt  for  an  equal  and  somewhat  problematic  saving.  *  Road  re- 
formers sometimes  overlook  the  fact  that  interest  is  a  yearly  charge 
and  that  the  debt  must  finally  be  paid. 

In  the  third  place,  the  cost  of  transportation  does  not  necessarily 
vary  proportionally  to  the  distance,  as  was  assumed  above.  If  the 
difference  in  distance  is  sufficient  to  make  a  difference  of  one  trip 
per  day,  then  the  value  of  the  saving  in  distance  is  tangible;  but 
where  the  saving  in  length  is  insufficient  for  an  additional  trip,  the 
value  of  the  difference  in  distance  depends  upon  the  value,  for 
other  work,  of  the  small  portions  of  time  of  men  and  teams  which 
may  be  saved  by  the  shorter  route, — a  value  which  exists,  but  which 
is  difficult  to  estimate. 

Therefore  any  estimate  as  to  the  value  of  a  saving  of  distance  is 
necessarily  only  a  rough  approximation ;  and  at  best  it  should  be 
used  only  as  a  guide  to  the  judgment. 

61.  The  problem  to  find  the  value  of  saving  distance  is  very 
different  for  wagon  roads  than  for  railroads.  In  the  case  of  railroads 
the  cost  of  the  various  elements  has  been  carefully  investigated  for 


50  ROAD    LOCATION.  [CHAP.   II- 

many  years,  and  the  transportation  is  all  conducted  under  a  single 
management  and  by  the  same  party  that  maintains  the  road  surface ; 
while  in  the  case  of  wagon  roads,  a  multitude  of  private  parties 
conduct  the  transportation  under  various  conditions,  and  the  main- 
tenance of  the  road  is  in  the  hands  of  public  officials. 

62.  GRADES.  A  level  road  is  the  most  desirable;  but  as  it  can 
seldom  be  obtained,  we  must  investigate  the  effect  of  grades  upon 
the  cost  of  constructing  and  operating  the  road,  and  also  determine 
what  is  the  steepest  allowable  grade. 

The  "grade  may  be  reduced  (1)  by  going  round  the  hill  or  by 
zigzagging  up  the  slope,  or  (2)  by  cutting  down  the  hill.  If  the 
slope  to  be  ascended  is  a  long  one,  the  first  method  must  be  em- 
ployed; but  if  the  grade  is  short,  the  second  is  usually  the  cheaper. 
Increasing  the  length  adds  to  the  cost  of  construction  and  of  trans- 
portation, while  cutting  down  the  hill  adds  only  to  the  cost  of 
construction.  The  maintenance  of  the  longer  and  flatter  line  may 
cost  either  more  or  less  than  the  shorter  and  steeper  one  according 
to  the  circumstances  of  the  case.  In  a  broken  or  rough  country, 
a  proper  adjustment  of  the  grades  is  the  most  important  part  of  the 
art  and  science  of  road  building ;  and  the  better  the  road  surface  the 
more  necessary  is  such  an  adjustment. 

63.  All  grades  are  objectionable  for  two  distinct  reasons,  viz.: 
because  a  grade  increases  the  amount  of  power  required  to  move  a 
load  up  it.  and  because  a  grade  may  be  so  steep  as  to  limit  the 
amount  of  the  load  that  can  be  moved  over  the  road.  The  first 
applies  to  all  grades  whatever  their  rate  or  height;  while  the  latter 
applies  only  to  the  steepest  grade  on  the  road,  and  in  a  measure  is 
independent  of  its  height  and  depends  only  on  its  rate.  At  present 
only  the  first  objection  to  grades  will  be  considered;  and  subse- 
quently the  second  objection  will  be  discussed  (see  §  71). 

64.  Effect  of  Grade  upon  Load  Table  10,  page  34,  shows  the 
load  (in  terms  of  the  weight  of  the  horse)  which  a  horse  with  a 
pull  equal  to  one  tenth  of  his  weight  can  draw  up  various  grades  on 
several  road  surfaces.  To  emphasize  the  effect  of  the  grade  upon 
the  load,  the  same  data  are  presented  in  a  slightly  differerrt  form  in 
Table  11,  page  34,  which  shows  at  a  glance  the  load  on  any  grade 
in  terms  of  the  load  on  the  level.  Tables  10  and  11  show  that  the 
better  the  condition  of  the  road  surface,  i.  e.,  the  less  the  rolling 


GRADES.  51 


resistance,  the  more  deleterious  a  grade.  For  example,  according 
to  Table  11,  on  iron  rails  on  a  3  per  cent  grade  a  horse  can  draw- 
only  10  per  cent  as  much  as  on  a  level;  while  on  a  broken-stone 
road  on  a  3  per  cent  grade  he  can  draw  25  per  cent  as  much  as  on 
a  level. 

A  horse  can  occasionally  and  for  a  short  time  exert  a  pull  equal 
to  more  than  one  tenth  of  his  weight.  If  the  grade  is  not  too  long9 
a  horse  can  safely  exert  a  force  equal  to  one  quarter  of  his  weight 
and  in  emergencies  one  half.  If  the  maximum  force  exerted  is  equal 
to  one  quarter  of  his  weight,  up  what  grade  can  he  pull  the  ordi- 
nary load? 

To  move  a  load  over  an  ordinary  earth  road  requires  a  tractive 
force  of  100  lb.  per  ton  (see  Table  9,  page  31),  and  therefore  a  team 
of  1200-pound  horses  exerting  a  force  equal  to  one  tenth  of  their 
weight  can  draw  2.4  tons  on  the  level.  The  reserve  power  to  take 
the  load  up  the  hill  is  (0.25-0.10) X  1200X2  =  360  pounds.  The 
total  load  to  be  carried  up  the  grade  is  the  wagon  and  its  load  plus 
the  weight  of  the  team,  or  2.4 +  (1200X2 -2000)  =  3.6  tons.  The 
grade  resistance  is  20  lb.  per  ton  for  each  per  cent  of  inclination 
(see  §  37) ;  and  the  grade  resistance  for  this  load  on  a  1  per  cent  grade 
is  3.6  X  20  =  72  lb.  Therefore,  the  grade  up  which  a  pull  of  360  lb. 
will  take  the  3.6  tons  is  360  -=-  72  =  5  per  cent,  which  is  the  maximum 
permissible  grade  for  an  earth  road  in  ordinary  condition.  The 
team  could  probably  pull  this  load  up  400  to  500  feet  of  such  a 


By  the  same  method  of  analysis,  the  load  for  the  same  team  on  a 
level,  muddy  earth  road  having  a  tractive  resistance  of  200  lb.  per 
ton  is  1.2  tons,  and  the  maximum  permissible  grade  is  7.5  per  cent. 

For  a  broken-stone  road  having  a  .tractive  resistance  of  33  lb. 
per  ton,  the  load  on  the  level  is  7.3  tons,  and  the  permissible  maxi- 
mum grade  is  2.2  per  cent. 

65.  What  load  can  the  above  team  take  up  a  4  per  cent  maxi- 
mum grade  on  a  broken-stone  road  having  a  tractive  resistance  of 
33  lb.  per  tonV  The  grade  resistance  is  20  X  4  =  80  lb.  per  ton; 
and  the  tractive  resistance  is  33  lb.  per  ton;  therefore  the  total 
resistance  *is  80  +  33  =  113  lb.  per  ton.  The  maximum  tractive 
power  of  the  team  is  equal  to  one  quarter  of  its  weight,  or  600  lb.; 
and  the  grade  resistance  for  the  weight  of  the  team  =  2400  •*■  2000  X 


52  ROAD    LOCATION.  [CHAP.   II. 

80  =  96  lb.;  therefore  the  net  tractive  power  of  the  team  is  600  — 
96  =  504  lb.  Then  the  weight  of  the  wagon  and  the  load  which  the 
team  can  draw  up  this  grade  is  504  -=-  113  =  4.4  tons. 

The  above  computations  are  for  two  1200-pound  horses,  but 
the  conclusions  would  not  materially  differ  for  horses  of  other 
weight. 

66.  Rise  and  Fall.  By  rise  and  fall  is  meant  the  vertical  height 
through  which  the  load  must  be  lifted  in  passing  over  the  road  in 
each  direction.  One  foot  of  rise  and  fall  is  a  foot  of  ascent  with  its 
corresponding  foot  of  descent.  In  passing  over  a  ridge  10  feet  high 
standing  in  the  middle  of  a  level  plain,  there  is  only  10  feet  of  rise 
and  fall;  and  not  10  feet  of  rise  plus  10  feet  of  fall.  If  the  road  is 
level,  Fig.  4,  then  an  elevation  or  depression  of,  say,  1  foot  produces 
literally  1  foot  of  rise  and  a  corresponding  foot  of  fall;  but  if  the 
road  is  on  a  steep  grade,  Fig.  5,  an  elevation  of  1  foot  above  the  grade 
line  or  of  a  like  amount  below  the  grade  line,  literally  speaking, 
produces  no  rise  and  fall,  because  in  either  case  it  is  a  continuous 


Fig.  4.  Fig.  5. 

up  grade.  However,  as  far  as  the  operation  is  concerned,  the  two 
cases  are  exactly  alike,  and  each  has  a  foot  of  rise  and  fall. 

Rise  and  fall  is  measured  by  the  number  of  vertical  feet  of  rise, 
as  shown  by  the  differences  of  elevation  on  the  profile. 

67.  The  introduction  of  rise  and  fall  is  a  question  either  (1) 
between  the  increased  cost  of  operation  and  the  increased  cost  of 
construction  required  to  fill  up  the  hollow  or  to  cut  down  the  hill, 
or  (2)  between  the  cost  of  operation  of  the  rise  and  fall  and  of  the 
increased  distance  necessary  to  go  around  the  obstruction. 

The  following  example  is  often  cited  as  showing  the  improve- 
ment that  can  be  made  in  locating  roads.  "An  old  road  in  Anglesea 
rose  and  fell  between  its  extremities,  24  miles  apart,  a  total  per- 
pendicular amount  of  3,540  feet;  while  a  new  road  laid  out  by  Telford 
between  the  same  points,  rose  and  fell  only  2,257  feet;  so  that  1,283 
feet  of  vertical  height  is  now  done  away  with,  which  every  horse 


GRADES.  53 


passing  over  the  road  had  previously  been  obliged  to  ascend  and 
descend  with  its  load.  The  new  road  is,  besides,  more  than  two 
miles  shorter.  Such  is  one  of  the  results  of  the  labors  of  a  skilful 
road  maker."  *  The  road  may  have  been  economically  re-located, 
but  the  citation  fails  to  show  whether  the  increased  cost  of  construc- 
tion to  eliminate  rise  and  fall  was  justified  by  the  decreased  cost  of 
operation. 

The  following  example  from  the  same  author,  also  frequently 
quoted,  shows  that  rise  and  fall  was  eliminated  by  increasing  the 
distance,  although  no  attempt  is  made  to  show  that  the  increased 
distance  was  more  economical  than  the  rise  and  fall  thereby  elimi- 
nated. "A  plank  road,  lately  laid  out  under  the  supervision  of 
Mr.  Geddes,  between  Cazenovia  and  Chittenango,  N.  Y.,  is  an  ex- 
cellent exemplification  of  the  true  principles  of  road  making.  Both 
these  villages  are  situated  on  the  Chittenango  Creek,  the  former 
being  800  feet  higher  than  the  latter.  The  most  level  wagon  road 
between  these  villages  rises  more  than  1,200  feet  in  going  from 
Chittenango  to  Cazenovia,  and  rises  more  than  400  feet  in  going 
from  Cazenovia  to  Chittenango,  in  spite  of  this  latter  place  being 
800  feet  lower.  It  thus  adds  one  half  to  the  ascent  and  labor  going 
in  one  direction;  and  in  the  other  direction  it  goes  up  hill  one  half 
the  height,  which  should  have  been  a  continuous  descent.  The 
line  of  the  plank  road  by  following  the  creek  (crossing  it  five  times) 
ascends  only  the  necessary  800  feet  in  one  direction,  and  has  no 
ascents  in  the  other,  with  two  or  three  trifling  exceptions  of  a  few 
feet  in  all,  admitted  in  order  to  save  expense.  There  is  a  nearly 
vertical  fall  in  the  creek  of  140  feet.  To  overcome  this,  it  was 
necessary  to  commence  far  below  the  falls,  to  climb  up  the  steep 
hillside,  following  up  the  sides  of  the  lateral  ravines  until  they  were 
narrow  enough  to  bridge,  and  then  turning  and  following  back  the 
opposite  sides  till  the  main  valley  was  again  reached.  The  extreme 
rise  is  at  the  rate  of  1  foot  to  the  rod  (1  in  16J),  and  this  only  for 
short  distances,  and  in  only  three  instances,  with  a  much  less  grade 
or  a  level  intervening."  f 

68.  Classes  of  Rise  and  Fall     In  discussing  the  effect  of  rise  and 


*  Roads  and  Road  Making,  W.  M.  Gillespie,  p.  36.     New  York,  1847. 
f  Ibid.,  p.  233-34. 


54  ROAD    LOCATION.  [CHAP.   II. 

fall  upon  the  operation  of  a  road  a  distinction  must  be  made  between 
three  classes  of  rise  and  fall,  as  follows: 

Class  A.  Rise  and  fall  on  grades  at  a  less  slope  than  the  angle 
of  repose  (the  grade  on  which  a  vehicle  by  its  own  weight  will  main- 
tain a  uniform  speed) ,  and  so  situated  as  not  to  require  any  addition 
to  the  total  power  required  to  move  a  load  over  the  road. 

Class  B.  Rise  and  fall  on  grades  so  steep  as  to  require  either  the 
holding  back  of  the  load  by  the  team  or  the  application  of  brakes. 

Class  C.     Rise  and  fall  on  the  maximum  grade. 

69.  An  example  of  the  first  class  of  rise  and  fall  is  shown  in 
Fig.  6.     The  team  is  relieved  on  the  down  grade  an  amount  exactly 

^_   _ equal  to   the   extra  tax  upon  the  up 

^-^^  grade,   and   the   only   effect   upon   the 

FlG"  6'  team  is  that  the  effort  is  concentrated 

on  the  up  grade  instead  of  being  uniformly  distributed  over  the  road ; 
but  as  the  slope  is  assumed  to  be  equal  to  or  less  than  the  angle  of 
repose,  the  maximum  effort  is  equal  to  or  less  than  twice  the  normal. 
If  the  grade  line  rises  above  the  level  instead  of  dipping  below  it, 
the  case  is  not  changed  except  that  the  rise  is  a  little  more  unfavor- 
ble,  since  the  team  has  no  relief  before  the  increase  in  effort  is 
required.     Therefore  this  class  of  rise  and  fall  costs  little  or  nothing. 

In  the  preceding  examples,  a  change  of  velocity  would  alter  the 
power  required  at  any  particular  instant;  but  in  wagon-road  traffic 
the  speed  is  always  small  and  consequently  the  effect  of  variations 
of  speed  are  quite  small,  and  may  be  entirely  neglected.  On  rail- 
roads a  variation  of  the  velocity  materially  affects  the  cost  of  rise 
and  fall. 

If  the  grade  is  greater  than  the  angle  of  repose,  the  team  in  de- 
scending must  hold  back  the  load,  which  is  lost  energy,  or  brakes 
must  be  applied,  which  tend  to  destroy  the  road ;  and  in  ascending, 
the  demand  upon  the  team  is  greater  than  twice  the  normal.  There- 
fore in  either  case  this  class  of  rise  and  fall  adds  to  the  cost  of  oper- 
ating the  road. 

If  the  grade  is  the  maximum,  it  may  be  sufficient  to  limit  the 
amount  of  the  load  a  team  may  draw  over  the  more  level  portions 
of  the  road,  and  therefore  greatly  add  to  the  cost  of  transportation. 
As  a  chain  is  no  stronger  than  its  weakest  link,  so  a  road  is  no  better 
than  its  steepest  grade. 


GRADES.  55 


70.  Cost  of  Rise  and  Fall.  What  does  it  cost  to  develop  the 
power  required  to  haul  a  load  up  a  grade  less  than  the  grade  of 
repose?     In  other  words,  what  is  the  cost  of  Class  A  rise  and  fall? 

The  cost  of  transportation  consists  chiefly  of  the  cost  of  driving, 
of  feed,  and  of  the  wear  and  tear  on  the  team.  Usually  the  cost  of 
driving  will  be  approximately  half  of  the  total  cost  of  transportation ; 
and  as  a  team  can  draw  a  load  up  the  grade  of  repose  at  practically 
the  same  speed,  at  least  for  short  stretches,  as  upon  the  level,  there 
will  usually  be  no  material  increase  in  the  cost  of  driving.  Even 
though  the  team  may  travel  slower  because  of  the  grade,  the  cost 
of  the  increased  time  can  scarcely  be  computed  because  of  the  im- 
possibility of  determining  the  value  of  fractions  of  time  for  other 
purposes.  The  cost  of  feed  and  of  wear  and  tear  on  the  team  must 
vary  approximately  as  the  total  power  developed.  Therefore  the 
conclusion  may  be  drawn  that  rise  and  fall  belonging  to  Class  A  will 
not  add  appreciably  to  the  cost  of  transportation.  This  conclusion 
is  corroborated  by  the  popular  belief  that  a  gently  undulating  road 
is  less  fatiguing  to  horses  than  one  which  is  perfectly  level.  The 
argument  in  support  of  this  belief  is  that  alternations  of  ascents, 
descents,  and  levels  call  into  play  different  muscles,  allowing  some 
to  rest  while  others  are  exerted,  and  thus  relieving  each  in  turn. 
The  argument  is  false,  and  probably  originated  in  the  prejudices  of 
man  in  his  quest  for  variety,  rather  than  in  the  anatomy  of  the  horse; 
but  the  above  theory  would  not  have  gained  its  wide  popularity 
if  a  gently  undulating  road  were  appreciably  more  fatiguing  to  a 
horse  than  a  perfectly  level  one.  A  perfectly  level  road  is  the  best 
for  ease  of  transportation. 

71.  If  the  grade  is  steeper  or  longer  than  that  up  which  the  team 
can  draw  the  normal  load  by  exerting  twice  the  tractive  power  re- 
quired on  the  level,  i.  e.,  if  the  rise  and  fall  belongs  to  Class  C,  then 
the  grade  has  the  effect  of  limiting  the  load  that  can  be  drawn  over 
the  level  portion  of  the  road,  and  consequently  increases  the  cost  of 
transportation.  The  load  which  a  team  can  draw  up  any  grade  can 
be  approximately  computed  as  in  §  65.  If  the  load  that  can  be 
drawn  up  any  particular  grade  is,  for  example,  three  fourths  of  the 
normal  load  on  the  level;  then  it  will  cost  as  much  to  haul  three 
fourths  of  a  load  with  this  grade  as  a  full  load  without  the  grade. 
If  the  cost  with  a  grade  less  than  the  maximum  is  10  cents  per  ton- 


56  KOA.D    LOCATION.  [CHAP.   II. 

mile  (see  §  4-7  and  §  20-21),  then  the  cost  with  the  maximum  grade 
will  be  10  -T-  |  =  13J  cents  per  ton-mile;  and  therefore  for  each  ton 
going  over  the  road,  the  maximum  grade  adds  3 J  cents  per  ton-mile. 
In  determining  the  amount  of  traffic,  only  full  loads  should  be 
included;  but  notice  that  the  full  load  varies  with  the  speed.  A 
ton  may  be  a  full  load  at  3  miles  per  hour,  while  half  a  ton  may  be  a 
full  load  at  6  miles  per  hour. 

Knowing  the  load  on  the  maximum  grade  and  also  the  cost  per 
ton-mile  for  a  level  road  or  for  a  grade  less  than  the  maximum,  the 
justifiable  expenditure  to  reduce  the  maximum  grade  may  be  com- 
puted as  follows :  The  difference  in  cost  per  ton-mile  with  and  with- 
out the  maximum  grade  may  be  determined  as  in  the  preceding 
paragraph;  and  this  multiplied  by  the  annual  number  of  loads 
going  over  the  road  gives  the  sum  that  may  be  spent  annually  to 
reduce  the  maximum  grade  to  the  lesser  value.  This  sum  may  be 
used  to  pay  interest  on  the  cost  of  cutting  down  the  hill  or  of  filling 
up  the  hollow. 

The  data  are  so  uncertain  that  the  result  must  be  regarded  only 
as  a  rough  approximation;  and  yet  it  is  worth  while  to  make  an 
investigation  as  above  as  a  guide  to  the  judgment. 

72.  Class  B  rise  and  fall  is  intermediate  between  Class  A  and 
Class  C,  and  its  cost  is  even  more  difficult  to  compute  than  that  of 
Class  C.  The  chief  difficulty  is  in  determining  the  relative  cost  of 
developing  power  on  a  level  and  up  a  grade.  Only  an  estimate  can 
be  made,  and  the  estimate  will  vary  greatly  with  the  point  of  view. 
For  example,  farmers  usually  have  a  surplus  of  power  (horses)  as 
far  as  transportation  is  concerned,  and  therefore  they  would  con- 
sider a  slight  increase  in  the  demand  for  power  as  a  matter  of  small 
moment.  Again,  teamsters  differ  greatly  as  to  what  is  a  proper 
or  economical  load  for  a  horse,  and  also  as  to  the  effect  of  a  tem- 
porary over-load. 

There  are  two  methods  of  computing  the  cost  of  this  class  of 
rise  and  fall,  neither  of  which  are  more  than  roughly  approximate. 

1.  Assume  that  the  cost  of  Class  B  rise  and  fall  bears  the  same 
relation  to  that  of  Classes  A  and  C,  that  the  grade  of  B  bears  to  that 
of  A  and  C.  Then  if  the  grade  for  Class  B  is  only  a  little  greater 
than  the  angle  of  repose,  the  cost  is  only  a  trifle  greater  than  that 


GRADES.  5? 


of  Class  A;  and  if  the  grade  is  neirly  a  maximum,  then  the  cost  of 
the  rise  and  fall  closely  approximatos  that  of  Class  C, 

2.  Assume  that  the  energy  developed  on  a  grade  over  and  above 
that  required  on  the  grade  of  repose,  co,?ts  the  same  per  unit  as  that 
of  an  equal  amount  of  energy  developed  on  the  level.  For  example, 
assume  that  the  rise  is  1  foot  more  than  the  angle  of  repose;  and 
assume  that  the  cost  of  drawing  a  load  on  a  good  broken-stone  road 
h  5  cents  per  ton-mile  (see  §  5-6),  and  that  the  tractive  power  is 
43  lb.  per  ton.  Then,  moving  a  ton  one  mile  will  develop  5,280  X 
40  =  211,200  foot-pounds  of  energy,  which  will  cost  5  cents.  The 
cost  of  one  foot-pound  of  energy,  then,  is  5-7-211,200  =  0.000,023,7 
cents.  Drawing  a  ton  over  a  rise  1  foot  high  develops  2,000  foot- 
pounds, the  cost  of  which  is  0.000,023,7 -2X2,000  =  0.023,7  cents. 
In  going  up  the  above  grade,  the  team  must  develop  enough  power 
to  move  the  load  up  the  grade  of  repose  and  in  addition  must  de- 
velop enough  to  lift  the  load  through  1  foot  vertically.  Therefore 
the  cost  of  the  1  foot  of  rise  assumed  above  is  0.023,7  cents  for  each 
ton  going  over  the  road. 

It  was  assumed  above  that  the  load  is  retarded  in  the  descent  by 
the  application  of  brakes;  but  if  the  grade  in  question  is  situated  in 
a  flat  country  where  brakes  are  not  usually  placed  upon  vehicles, 
the  team  must  hold  back  on  the  descent  an  amount  equal  to  the 
extra  energy  required  on  the  ascent,  and  therefore  the  cost  of  the 
foot  of  rise  and  fall  will  be,  almost  or  quite,  doubled. 

With  data  similar  to  the  above,  and  with  a  knowledge  of  the 
amount  of  traffic,  it  is  a  simple  arithmetical  process  to  compute  the 
sum  that  may  be  spent  annually  to  eliminate  one  or  more  feet  of 
rise  and  fall.  Notice  that  in  this  case  only  the  full  loads  should  be 
considered  (see  the  first  paragraph  of  §  71).  For  example,  assume 
that  a  broken-stone  road  has  a  traffic  of  20  tons  per  day  one  way  for 
300  days  of  the  year,  or  an  annual  traffic  of  20  X  300  =  6,000  tons. 
The  cost  of  a  foot  of  rise  and  fall  per  ton  of  traffic  is  0.023,7  cents, 
and  the  annual  cost  on  this  particular  road  is  0.000,237X6,000= 
$1.42.  This  is  the  amount  which,  according  to  the  above  inves- 
tigation, can  be  spent  annually  to  cut  down  the  hill  or  to  fill  up 
the  hollow  sufficiently  to  eliminate  1  foot  of  rise  and  fall. 

Similarly,  for  an  earth  road  having  a  cost  of  15  cents  per  ton-mile 
and   a  tractive  power  of  100  pounds  per  ton,  1  foot  of  rise  costs 


58  KOAD    LOCATION".  [CHAP.   II. 

0.028,4  cents,  and  tho  foot  of  ascent  assumed  above  will  cost  0.02S.4 
cents  for  each  ton  going  over  the  road.  If  this  road  has  a  traffic 
of  5  tons  one  way  for  300  days  of  th^  year,  the  annual  cost  of  the 
foot  of  rise  and  fall  is  0.028,4X  5X  300  =  44.6  cents,  which  is  the  sum 
that  can  be  spent  annually  to  eliminate  the  foot  of  rise  and  fall. 

From  the  point  of  view  of  the  last  solution,  it  appears  that  the 
cost  of  Class  A  rise  and  fall  increases  with  the  steepness  of  the  grade, 
that  is,  increases  as  the  rate  of  the  grade  approaches  the  angle  of 
repose.  In  all  probability  this  is  correct,  but  all  the  data  involved 
are  too  uncertain  to  warrant  any  further  discussion  of  the  subject 
here.  However,  the  engineer  should  bear  such  relations  in  mind 
in  solving  a  particular  problem. 

73.  Distance  vs.  Rise  and  Fall.  In  locating  a  road  the  question 
may  arise  between  the  relative  desirability  of  introducing  rise  and 
fall  and  of  increasing  the  length  of  the  line.  The  problem  then  is 
to  determine  the  relative  value  of  distance  and  of  rise  and  fall. 

If  the  conclusion  in  §  70  is  correct,  that  the  cost  of  Class  A  rise 
and  fall  is  not  appreciable,  then  the  distance  should  not  be  increased 
at  all  to  eliminate  Class  A  rise  and  fall. 

74.  For  Class  B  rise  and  fall  an  approximate  solution  can  be 
obtained  by  assuming  that  it  costs  the  same  to  develop  a  certain 
amount  of  energy  in  overcoming  Class  B  rise  and  fall  as  to  develop 
a  like  amount  of  energy  in  moving  a  load  on  a  level  road.  This 
assumption  is  probably  reasonably  correct. 

For  example,  the  tractive  resistance  of  the  best  broken-stone 
road  is  33  pounds  per  ton,  and  the  work  necessary  to  raise  1  ton 
through  1  foot  of  rise  is  2,000  foot-pounds;  therefore  to  develop 
2,000  foot-pounds  of  work  on  a  level  broken-stone  road,  a  ton  must 
be  moved  2,000  -f-  33  =60  feet.  Hence  the  cost  of  operating  60  feet 
of  distance  on  this  road  may  be  considered  as  equivalent  to  1  foot 
of  rise  and  fall.  Therefore  to  eliminate  a  foot  of  rise  and  fall  of 
Class  B,  the  length  of  the  road  may  be  increased  60  feet.  Table  12, 
page  59,  gives  the  corresponding  distance  for  other  road  surfaces.* 

*  The  above  relations  are  for  a  load  transported  on  wheels.  It  may  be  interest- 
ing to  know  the  corresponding  relations  for  pedestrians.  The  work  (energy)  re- 
quired of  a  man  in  walking  is  practically  independent  of  the  nature  of  the  road 
surface.  A  man  makes  progress  in  walking  by  allowing  his  body  to  fall  through  a 
small  space  and  then  raising  it  again  preparatory  to  another  fall.    For  an  average 


GRADES.  59 


.  .      10  feet 

. .      20 

tt 

.  .      25 

1 

. .      50 

tt 

..     25 

it 

.  .      40 

a 

.  .      25 

tt 

. .      60 

" 

. .     40 

tt 

. .     80 

it 

. .   100 

tt 

. .  200 

tt 

TABLE  12. 
Horizontal  Distance  Equivalent  to  1  Foot  of  Class  B  Rise  and  Fall. 

Earth  roads,  muddy (tractive  resistance  200  lb.  per  ton). 

"      ordinary "  100  "  "  " 

"      dry  and  hard "  80"  "  "  .. 

Stone-block  pavement,  best "  40"  "  "  . . 

ordinary "  80  "  "  "  . 

Gravel,  best "  50"  "  "  . 

"       ordinary «  80  "  "  "  . , 

Broken-stone  road,  best "  33  "  "  "  . 

"     ordinary "  50  "  "  "  . 

Brick  on  concrete "  25  "  "  "  .  , 

Sheet  asphalt "  20  "  "  "  . 

Iron  rails,  clean "  10  "  "  "  . 

75.  Apparentl}r  writers  on  roads  have  not  made  a  distinction 
between  the  several  classes  of  rise  and  fall.  Herschel  says:  *  "To 
determine  whether  it  is  more  advisable  to  go  over  than  around  a 
hill,  all  other  considerations  being  equal,  we  have  this  rule:  Call  the 
difference  between  the  distance  around  on  a  level  and  that  over  the 
hill  d  (the  distance  around  being  taken  as  the  greater),  and  call  h 
the  height  of  the  hill.  Then  in  case  of  a  first-class  road,  we  go  round 
when  d  is  less  than  16ft;  and  in  case  of  a  second-class  road,  we  go 
round  when  d  is  less  than  \(MP  Although  not  specially  so  stated, 
ihe  above  rule  was  plainly  intended  for  broken-stone  roads. 

The  above  rule  (which  has  been  frequently  quoted)  recognizes 
no  distinction  between  the  several  classes  of  rise  and  fall.  It  makes 
the  avoidance  of  a  foot  of  rise  in  going  over  a  small  culvert  or  of  a 
foot  of  fall  in  crossing  an  open  ditch,  equally  as  important  as  the 
elimination  of  a  foot  of  rise  and  fall  on  the  maximum  grade  It  i3 
not  possible  to  draw  sharp  lines  between  the  several  classes  of  rise 
and  fall,  but  it  is  certain  that  there  is  a  great  difference  in  cost  be- 
tween a  foot  of  rise  and  fall  on  a  flat  grade  and  the  same  quantity 
on  the  maximum  or  limiting  grade.  Notice  that  the  above  rule 
makes  the  horizontal  distance  equivalent  to  a  foot  of  rise  much  less 
than  that  stated  in  Table  12  above. 

man,  the  energy  expended  in  walking  16  to  20  feet  horizontally  is  sufficient  to  raise 
his  body  through  1  foot  vertically.  Therefore,  for  pedestrians  1  foot  of  rise  and 
fall  is  equivalent  to,  say,  18  feet  of  horizontal  distance. 

♦Clemens  Herschel,  Science  of  Road  Making,  Prize  Essay  of  the  State  Board  of 
Agriculture  of  Massachusetts,  Boston,  1869,  p.  207-63;  revised  edition,  Engineering 
News,  New  York,  1890,  p.  9. 


60  KOAD    LOCATION.  [CHAP.   II. 

76.  Maximum  Grade.  The  fixing  of  the  proper  maximum  or 
ruling  grade  is  the  most  important  matter  connected  with  the  loca- 
tion of  a  road.  To  do  this  intelligently,  the  maximum  grade  must  be 
considered  both  as  an  ascent  and  also  as  a  descent.  Viewed  as  an 
ascent,  the  maximum  or  ruling  grade  chiefly  concerns  the  draught  of 
heavy  loads;  and  viewed  as  a  descent,  it  chiefly  concerns  the  safety 
of  rapid  traveling.  In  both  respects,  the  effect  of  the  grade  in 
limiting  the  load  depends  upon  its  rate,  and  is  practically  inde- 
pendent of  its  height. 

77.  As  an  Ascent.  The  load  which  a  team  can  draw  over  any 
road  is  determined  by  the  length  and  steepness  of  the  maximum 
grade;  or,  in  other  words,  the  length  and  rate  of  the  permissible 
maximum  grade  depends  upon  the  endurance  of  the  team.  The 
method  of  computing  the  load  that  a  team  can  draw  up  any  grade 
was  explained  in  §  65,  page  51.  That  investigation  shows  that  the 
maximum  grade  varies  greatly  with  the  conditions  of  the  surface; 
and  that  the  better  the  surface  the  less  should  be  the  ruling  grade. 
In  other  words,  unless  the  maximum  grade  is  light,  the  amount  that 
can  be  hauled  on  a  broken-stone  road  does  not  differ  greatly  from 
that  on  an  earth  road. 

The  team  could  probably  pull  the  maximum  load  up  a  stretch 
of  the  maximum  grade  400  to  500  feet  long;  and  if  the  maximum 
grade  does  not  occur  too  often,  it  could  probably  pull  the  load  up  a 
stretch  two  or  three  times  as  long.  On  long  maximum  grades,  it  is 
wise  to  provide  a  little  stretch  of  nearly  level  grade  upon  wyhich  to 
let  the  team  rest.  In  the  above  computation,  the  team  is  assumed 
to  have  a  reserve  power  equal  to  that  exerted  on  the  maximum 
grade;  but  the  power  required  to  start  the  load  may  be  four  or 
five  times  the  normal  tractive  resistance,  and  hence  a  nearly  level 
resting  place  is  required,  so  that  the  team  may  readily  start  the 
load. 

78.  Many  of  the  books  on  roads  state  that  if  the  maximum  grade 
is  long,  the  slope  should  be  flattened  toward  the  summit  to  com- 
pensate for  the  decreased  strength  of  the  fatigued  horses.  This 
recommendation  is  both  improper  and  impracticable.  It  is 
improper,  since  it  assumes  that  if  the  horse  is  to  develop  energy  to 
lift  the  load  up  the  incline,  he  should  not  work  at  a  uniform  rate. 
Universally  the  race  horse  goes  fastest  on  the  home  stretch;  and  if 


GRADES.  61 


he  is  .urged  to  his  utmost  speed  at  first,  he  is  sure  to  lose  the  race. 
The  recommendation  is  impracticable,  since  the  topography  would 
rarely  permit  the  flattening  of  the  grade  at  the  top  without  in- 
creased expense,  and  it  would  not  be  wise  to  incur  extra  cost  for  this 
purpose. 

79.  If  the  loads  are  much  heavier  in  one  direction  than  in  the 
other,  it  is  permissible  to  oppose  the  lighter  traffic  with  the  steeper 
ruling  grade. 

80.  As  a  Descent.  Viewed  as  a  descent,  the  maximum  grade 
concerns  chiefly  the  safety  of  rapid  traveling.  Many  of  the  writers 
on  roads  claim  that  the  descending  grade  should  not  exceed  the 
angle  of  repose,  i.  e.,  should  not  exceed  the  inclination  down  which 
the  vehicle  will  descend  by  its  own  weight.  This  limit  is  impracti- 
cable, since  the  angle  of  repose  varies  with  the  kind  of  vehicle, 
degree  of  lubrication,  amount  of  load,  size  of  wheels,  etc.  Besides, 
this  limitation  is  unnecessary,  since  the  resistance  of  traction  in- 
creases as  the  speed,  and  in  going  down  it  is  only  necessary  to  drive 
faster  to  prevent  the  vehicle  from  unduly  crowding  upon  the  team  ; 
but  of  course  this  remedy  has  its  limitations.  Further,  the  speed 
in  descending  may  be  checked  by  the  application  of  the  brake ;  but 
it  should  be  remembered  that  the  use  of  the  brake  is  detrimental 
to  the  road  surface,  particularly  on  the  maximum  grade. 

On  Ordinary  roads,  grades  twice  as  steep  as  the  angle  of  repose 
are  operated  without  inconvenience 'or  danger.  In  Europe  it  is 
usually  assumed  that  on  a  good  broken-stone  road,  of  which  the 
angle  of  repose  is  about  2  or  2\  per  cent,  a  5  per  cent  grade  is  the 
maximum  that  can  be  descended  safely  at  a  trot  without  brakes; 
and,  if  the  stretch  is  long,  3  per  cent  is  considered  the  maximum  for 
safety.  On  mountain  roads  having  a  broken-stone  surface,  freight 
wagons  descend  12  per  cent  grades  by  the  use  of  brakes,  but  with 
expert  drivers. 

81.  Examples  of  Maximum  Grades  for  Earth  Roads.  For  ob- 
vious reasons  there  are  not  much  data  under  this  head.  In  hilly 
country  short  grades  of  1  in  3  (33%)  are  occasionally  found — par- 
ticularly in  a  new  country, — and  grades  of  1  in  4  (25%)  are  some- 
what common.  In  comparatively  flat  country,  grades  of  1  in  8 
(12J%)  are  not  infrequent. 

In  improving  the  celebrated  Holyhead  road,  Telford  found  in 


62  ROAD    LOCATION.  [CHAP.  II. 

old  roads  many  grades  of  1  in  6  and  1  in  7.  A  number  of  roads 
improved  by  state  aid  in  New  Jersey  originally  had  grades  of  14 
per  cent.  Of  course,  only  the  roads  having  the  most  traffic  were 
improved;  and  less  frequented  roads  in  the  same  locality  have 
much  greater  grades. 

82.  Examples  of  Maximum  Grades  on  Broken-stone  Roads.  In 
Prussia  the  standard  is:  in  mountainous  country  1  in  20  (5%),  in 
hilly  country  1  in  25  (4%),  and  in  level  country  1  in  40  (2£%). 

In  Hanover  the  regulations  are:  in  mountainous  country  1  in 
25  (4%),  in  hilly  country  1  in  30  (3J%),  and  in  level  country  1  in 
40  (2i%). 

In  Baden  the  standard  is :  main  highways  5  per  cent,  secondary 
roadways  6  per  cent,  and  mountain  roads  8  per  cent. 

In  Brunswick  the  regulations  are:  on  the  plains  1  in  33J  (3%), 
in  hilly  country  1  in  25  (4%),  and  in  mountainous  country  1  in  18 
(5i%). 

In  France  the  standard  is:  on  national  roads,  not  exceeding 
3  per  cent;  departmental  roads,  not  exceeding  4  per  cent;  and 
subordinate  roads,  not  exceeding  6  per  cent.  On  the  great  Alpine 
road  over  the  Simplon  Pass,  built  under  the  direction  of  Napoleon 
Bonaparte,  the  grades  average  1  in  22  (4£%)  on  the  Italian  side, 
and  1  in  17  (5.9%)  on  the  Swiss  side,  and  in  only  one  case  become 
as  steep  as  1  in  13  (7.7%). 

In  Great  Britain,  the  celebrated  Holyhead  road,  built  by  Tel- 
ford through  the  very  mountainous  district  of  North  Wales,  has  an 
ordinary  maximum  of  1  in  30  (3J%),  with  one  piece  of  1  in  22  (4£%) 
and  a  very  short  piece  of  1  in  17  (5.9%),  on  both  of  which  pieces 
special  care  was  taken  to  make  the  surface  harder  and  smoother 
than  on  the  remainder  of  the  road. 

On  the  National  Pike  over  the  Alleghenies,  built  before  the  intro- 
duction of  the  railroad,  the  maximum  was  7  per  cent.  At  an  early 
day  the  New  York  law  limited  the  grades  of  turnpikes  (toll  roads)  to 
1  in  11  (9%). 

In  New  York  on  state-aid  roads  the  nominal  maximum  is  5  per 
cent,  but  grades  as  steep  as  64  per  cent  have  been  found  necessary 
in  some  cases.  In  New  Jersey  are  a  number  of  state-aid  roads  hav- 
ing grades  of  7  and  8  per  cent,  and  one  of  lOf  per  cent.  In  Massa- 
chusetts no  hard-and-fast  standard  has  been  adopted  for  the  state- 


GRADES.  63 


aid  roads,  but  a  few  have  5  per  cent  grades  and  a  considerable  num- 
ber have  4  per  cent.  It  is  said  that  on  some  important  roads  the 
grade  can  not  at  reasonable  expense  be  reduced  below  7  per  cent. 

83.  In  improving  city  streets  it  is  often  impossible  to  make  any 
radical  change  in  the  grade  owing  to  the  resulting  damage  to  abut- 
ting property,  and  it  is  always  impossible  to  avoid  the  steep  grade 
by  a  change  of  location;  and  consequently  some  city  streets  have 
very  steep  grades  which  are  used  with  surprisingly  good  results. 
Newton,  Mass.,  has  a  number  of  macadamized  streets  which  have 
long  stretches  of  9  and  10  per  cent  grades,  and  has  one  12  per  cent 
grade  1,000  feet  long.  Waltham,  Mass.,  has  one  400-foot  stretch  of 
macadam  on  a  12  per  cent  grade,  and  another  on  a  13  per  cent 
grade.  In  the  Borough  of  Richmond  (Staten  Island),  New  York 
City,  are  several  pieces  of  10,  11,  and  12  per  cent  grades,  and  100 
feet  of  14  per  cent,  two  stretches  of  200  feet  each  of  16  per  cent,  and 
one  piece  200  feet  long  of  20  per  cent  grade. 

84.  For  mountain  roads  where  the  bulk  of  the  traffic  is  down 
hill,  the  maximum  grade  is  often  8  per  cent  and  sometimes  as  much 
as  12  per  cent.  "  Experience  in  heavy  freighting  has  shown  that 
wagons  can  be  satisfactorily  controlled  in  all  weathers  on  12  per 
cent  grades,  but  they  can  not  be  safely  controlled  on  steeper  grade." 

85.  For  pleasure  driving,  the  grade  of  a  good  gravel  or  broken- 
stone  road  should,  if  practicable,  not  exceed  4  per  cent.  A  good 
horse  with  a  light  buggy  and  two  persons  will  easily  trot  up  this 
grade,  and  also  trot  down  without  a  brake;  but  with  a  steeper 
grade  the  strain  in  either  direction  is  unduly  great. 

For  bicycle  travel,  a  2  per  cent  grade  can  be  ascended  with  com- 
parative ease  and  descended  with  but  little  effort.  Heavier  grades, 
up  to  5  per  cent,  can  be  ascended  by  the  average  bicycle  rider  with- 
out extreme  effort  and  descended  without  serious  danger.  A  5  per 
cent  grade  should  be  used  only  when  unavoidable,  and  steeper 
grades  can  not  be  ascended  with  reasonable  effort  or  descended  with 
assured  safety. 

86.  Minimum  Grade.  Considering  only  the  cost  of  transporta- 
tion, a  perfectly  level  road  is  the  best;  but  it  costs  less  to  maintain 
a  road  upon  a  slight  grade  than  one  perfectly  level.  All  roads 
should  be  higher  in  the  center  than  at  the  sides,  so  as  to  shed  the 
rain  to  the  side  ditches,  but  on  any  road  longitudinal  ruts  are  lia- 


64  ROAD    LOCATION".  [CHAP.   II. 

ble  to  form  and  interfere  with  the  surface  drainage ;  and  therefore  if 
the  road  is  perfectly  level  in  its  longitudinal  direction,  its  surface 
can  not  be  kept  free  from  water  without  giving  it  so  great  an  incli- 
nation transversely  as  to  expose  vehicles  to  the  danger  of  overturn- 
ing. On  a  perfectly  level  road,  every  rut  will  hold  water,  which  will 
soak  into  the  road  and  soften  it  whether  it  be  earth  or  broken  stone ; 
whereas  with  even  a  slight  longitudinal  grade,  every  wheel  track 
becomes  a  channel  to  carry  off  the  rain  water.  It  is  a  common  ob- 
servation that  earth  roads  running  up  hill  and  down  dale  are  better 
to  travel  upon  than  more  level  ones.  This  is  largely  due  to  the 
better  longitudinal  surface  drainage. 

The  harder  the  road  material  the  less  the  necessity  for  longitudi- 
nal drainage  of  the  surface.  An  earth  road-surface  is  certain  to 
wear  into  ruts,  and  hence  is  greatly  benefited  by  having  a  longi- 
tudinal slope.  Gravel  and  broken-stone  roads  are  liable  to  wear 
into  longitudinal  ruts,  and  hence  need  longitudinal  drainage. 
Broken-stone  roads  built  with  the  hardest  limestones  or  trap  are 
not  easily  worn  into  ruts,  and  therefore  the  necessity  for  a  longi- 
tudinal grade  is  least  with  this  class  of  construction. 

A  longitudinal  grade  decreases  the  cost  of  maintenance,  and  the 
advisability  of  introducing  a  grade  for  such  a  purpose  depends  upon 
the  relative  cost  of  constructing  it  and  upon  the  capitalized  value 
of  the  cost  of  maintaining  it.  With  earth  roads  the  expenditures 
for  maintenance  are  ordinarily  too  slight  to  justify  much  expense  in 
securing  a  longitudinal  grade;  but  with  high  class  broken-stone 
roads,  which  naturally  have  a  heavy  traffic,  a  considerable  expense 
to  secure  a  slight  longitudinal  grade  is  usually  justifiable.  Engi- 
neers whose  experience  has  been  largely  upon  railroads  and  canals 
are  prone  to  spend  money  to  secure  an  absolutely  level  road,  where 
a  slight  grade  could  be  secured  at  a  less  expense.  In  filling  up  a 
hollow  or  cutting  down  a  hill,  the  employment  of  a  light  longitudinal 
grade  may  decrease  the  cost  of  construction  and  also  the  cost  of 
maintenance  without  increasing  the  cost  of  transportation  (§  68-70). 
The  important  principle  to  remember  is  that  a  slight  longitudinal 
grade  is  an  advantage ;  although  over  a  long  stretch  of  level  country 
it  may  not  be  practicable  to  secure  it. 

The  following  is  the  minimum  grade  adopted  by  leading  engi- 
neers for  broken-stone  roads:  in  England  1  in  80,  or  1J  per  cent;  in 


CURVES. — WIDTH.  65 


France,  by  the  Corps  des  Ponts  et  Chaussees,  1  in  125,  or  0.8  per  cent; 
in  the  United  States  1  in  200,  or  0.5  per  cent. 

87.  CURVES.  Theoretically  the  shortest  radius  of  curvature 
allowable  on  roads  depends  upon  the  width  of  the  road,  and  upon  the 
maximum  length  of  teams  frequenting  the  road  or  upon  the  speed 
of  the  shorter  teams.  Since  the  length  of  a  four-horse  team  and 
vehicle  is  about  50  feet,  to  permit  such  a  team  to  keep  upon  a  12- 
foot  roadway  would  require  a  radius  of  the  inside  of  the  curve  of 
about  100  feet;  on  a  16-foot  roadway  a  radius  of  about  75  feet 
would  be  required;  and  on  an  18-foot  roadway,  a  radius  of  about  65 
feet.  In  France  the  minimum  radius  is  as  follows:  on  main  and 
departmental  roads  of  which  the  trackway  is  20  to  22  feet  wide,  165, 
and  in  extreme  cases  100  feet;  on  principal  country  roads  which  are 
20  feet  wide,  50.  In  Saxony  the  minimum  radius  on  principal  roads 
is  82  feet,  and  on  ordinary  country  roads  it  is  40  feet. 

"On  mountain  roads  with  grades  of  1  or  2  per  cent,  heavy  teams 
require  curves  of  40  feet  radius,  and  light  ones  30  feet;  and  with 
grades  of  3  or  4  per  cent,  heavy  teams  require  65  and  light  ones  50 
feet."  *  "In  extreme  cases  on  mountain  roads  four-  and  six-horse 
teams  haul  maximum  loads  over  16-foot  roads  having  a  radius  at 
their  outer  edge  of  30  feet."  However,  in  this  case  the  roads  on 
the  curves  must  be  level,  as  the  rear  team  is  expected  to  do  all  of 
the  pulling. 

88.  WIDTH.  Under  this  head  will  be  considered  primarily  the 
width  of  the  right  of  way,  the  width  of  the  wheelway,  or  improved 
portion,  being  considered  later,  in  the  chapter  relating  to  the  par- 
ticular road  surface. 

The  legal  width  of  right  of  way  varies  greatly  in  different  states. 
In  an  early  day,  before  any  attempt  was  made  to  improve  the  wheel- 
way,  the  legal  width  was  often  100  feet,  and  sometimes  10  rods 
(165  feet).  In  some  of  the  states  where  land  is  cheap,  the  former 
width  still  prevails  to  some  extent.  In  most  of  the  states  of  the 
Mississippi  Valley,  particularly  those  in  which  the  land  was  divided 
according  to  the  system  of  U.  S.  public  land  surveys,  the  legal  width 
of  right  of  way  is  usually  66  feet.     A  few  of  these  states  classify  the 


*  Prize  Essay  on  Road  Making,  Clemens  Herschel,  Massachusetts  State  Board  of 
Agriculture,  Report  for  1869,  p.  207-63. 


66  ROAD    LOCATION.  [CHAP.   II. 

roads,  making  the  less  frequented  ones  narrower;  for  example,  in 
Texas  the  widths  of  first,  second,  and  third  class  roads  are  60,  30, 
and  20  feet  respectively.  In  the  earlier  settled  states  along  the 
Atlantic  coast,  3  rods  (49£  feet)  is  a  common  width,  although  some 
of  the  less  frequented  roads  are  only  2  rods  (33  feet)  wide. 

If  the  surface  is  loam  or  clay,  a  considerable  width  of  traveled 
way  is  required  that  the  traffic  may  not  cut  the  surface  up  so  badly 
when  it  is  soft.  This  is  probably  the  explanation  of  the  60  or  66 
feet  so  common  in  the  Mississippi  Valley.  In  some  of  the  states, 
for  example,  Illinois,  the  law  specifies  that,  "if  possible,"  a  strip 
equal  in  width  to  one  tenth  of  the  right  of  way  shall  be  reserved  for 
pedestrians  on  each  side  between  the  property  line  and  the  ditch. 
This  leaves  53  feet  for  the  wheelway  and  ditches,  which  is  probably 
none  too  much  for  a  loam  or  clay  road.  If  the  ditches  are  deep  and 
consequently  wide,  the  sidewalk  is  usually  curtailed  rather  than  the 
wheelway. 

In  Massachusetts  the  roads  improved  by  state  aid  usually  have  a 
width  of  right  of  way  of  50  feet,  and  in  localities  where  there  was  a 
possibility  of  space  being  required  by  an  electric  road  they  are  60 
feet,  the  latter  being  considered  sufficient  to  accommodate  a  double- 
track  electric  road,  wagon  ways,  and  sidewalks. 

89.  In  England  the  principal  roads,  especially  those  near  popu- 
lous cities,  are  laid  out  66  feet  wide,  20  or  22  feet  being  covered 
with  broken  stone.  Telford's  celebrated  Holyhead  road,  a  model 
road  for  a  hilly  country,  has  a  width  of  32  feet  in  flat  country  and 
22  feet  along  steep  ground  and  precipices. 

In  Holland  the  usual  width  is  38  feet,of  which  14  feet  is  improved. 
In  France  the  standard  widths  are  as  follows,  to  the  nearest  foot : 

Class  of  Road.  Right  of  Way.  Width  Improved. 

National  roads 66  feet  22  feet 

Departmental  roads 40    "  20    " 

Provincial  *     33    "  20    " 

Neighborhood     "    26    "  16    " 

90.  CROSS  SECTION.  The  cross  section  of  a  road  depends  upon 
the  material  of  the  road  surface,  and  hence  will  be  considered  in  the 
respective  chapters  following. 

91.  PLACING  THE  LINE.  The  controlling  points  of  a  line  are 
certain  points  at  which  the  position  of  the  road  is  restricted  within 


PLACING    THE    LINE.  67 


narrow  limits  and  is  not  subject  to  change.  These  may  be  points 
where  the  location  is  governed  by  the  necessity  of  providing  an  out- 
let for  the  traffic,  or  points  where  the  position  of  the  line  is  restricted 
by  topographical  considerations — such  as  a  summit  over  which  the 
road  must  pass,  or  a  suitable  location  for  a  bridge. 

After  the  reconnoissance  of  the  locality  is  completed  and  the 
position  and  elevation  of  the  controlling  points  are  known,  the  line 
must  be  marked  upon  the  ground.  For  example,  assume  that  it  is 
desired  to  run  a  road  from  A  to  D,  Fig.  7,  page  68,  D  being  a  pass 
over  the  ridge.  If  the  road  follows  the  line  A  B  C  D,  it  will  have 
the  profile  shown  near  the  bottom  of  Fig.  7.  The  average  grade 
from  A  to  B  is  1  per  cent,  and  from  B  to  C  5  per  cent.  If  it  is  de- 
sired to  locate  a  road  that  shall  have  a  grade  no  steeper  than  5  per 
cent,  we  may  begin  at  D  and  locate  a  line  having  an  uniform  5  per 
cent  grade.  It  is  best  to  commence  the  location  from  D,  since 
usually  the  slopes  nearer  the  foot  of  the  hills  are  flatter  than  those 
at  the  summit,  and  consequently  there  is  more  choice  of  position  of 
the  line  there  than  at  the  summit.  Frequently  in  rough  country, 
the  only  controlling  point  fixed  before  beginning  the  location  survey 
is  the  lowest  pass  over  a  ridge  or  mountain  range. 

Beginning  at  D,  a  line  may  be  located  either  (1)  by  setting  off 
the  angle  of  the  gradient  on  the  vertical  circle  of  a  transit  or  on  a 
gradienter,*  and  sighting  upon  a  rod  which  is  moved  until  the  line 
of  sight  strikes  it  at  the  same  height  from  the  ground  that  the  instru- 
ment is  above  grade;  or  (2)  the  points  for  the  line  may  be  found 
by  running  a  line  of  levels  ahead  of  the  transit,  and  measuring  the 
distances  by  which  to  reckon  the  rate  of  the  grade.  The  line  DEC, 
Fig.  7,  has  a  uniform  gradient  of  5  per  cent. 

If  a  contour  map  is  at  hand,  the  line  can  be  located  approxi- 
mately by  opening  a  pair  of  dividers  until  the  distance  between  the 
points  corresponds  to  100  feet,  setting  one  point  on  the  place  of 
beginning  and  the  other  on  the  next  lower  contour,  which  gives  a 
line  100  feet  long  with  a  grade  equal  to  the  distance  between  con- 
tours— in  Fig.  7,  five  feet. 

The  fine  D  F  G  has  a  uniform  grade  of  5  per  cent.     From  H  to  A 

♦Baker's  Engineer's  Surveying  Instruments,  p. 209-16. 


68 


ROAD   LOCATION. 


[CHAP.   II. 


PLACING    THE    LIKE.  69 


the  road  will  have  considerably  less  grade  than  5  per  cent,  and  can 
have  a  comparatively  wide  range  of  position. 

The  average  grade  from  A  to  D  is  a  little  less  than  5  per  cent,  but 
the  slopes  are  so  steep  between  D  and  C  that  it  is  impossible,  within 
the  limits  of  the  map,  to  locate  such  a  line.  If  such  a  gradient  is 
located  from  D  toward  A,  it  will  necessarily  make  a  number  of  short 
turns  on  itself,  which,  although  undesirable,  are  sometimes  un- 
avoidable. These  short  turns  seriously  impede  traffic,  since  vehi- 
cles can  not  easily  pass  each  other  on  such  short  curves — particu- 
larly if  each  is  drawn  by  a  long  team.  Short  turns  are  also 
dangerous  in  descending,  in  case  control  of  the  vehicle  is  lost  or  the 
team  runs  away. 

92.  The  line  A  B  C  D  may  be  considered  as  an  old  road  which  it 
is  proposed  to  improve  by  reducing  the  grades.  Substituting  the 
line  C  E  D  for  C  D  changes  the  maximum  grade  from  10  to  5  per 
cent. 

93.  In  placing  the  line  attention  should  be  given  to  the  nature 
of  the  soil  on  alternative  lines,  since  on  one  side  of  the  valley  the 
surface  may  be  clay,  upon  the  opposite  gravel;  in  the  bottom  of 
the  valley  the  soil  is  usually  alluvial,  while  higher  up  it  is  generally 
better  for  road  purposes.  It  should  be  remembered  that  in  almost 
all  steep  slopes  covered  with  loose  material,  the  debris  is  either  slowly 
moving  down  the  slope  or  has  attained  a  state  of  repose  so  deli- 
cately adjusted  that  an  excavation  for  a  road-bed  on  the  inclined 
surface  will  again  set  the  mass  in  motion.  Such  movements  are 
particularly  common  in  loose  materials  in  countries  where  the  frost 
penetrates  deeply  and  the  ground  becomes  very  soft  when  thawing, 
and  frequently  entail  long-continued  and  serious  expense  in  main- 
tenance. 

If  the  road  is  to  have  a  surface  of  gravel  or  broken  stone,  the 
relative  proximity  of  the  materials  for  the  original  construction  as 
well  as  for  repairs  should  be  considered  in  deciding  between  possible 
locations.  However,  it  should  be  remembered  that  after  the  road 
is  completed,  the  amount  of  hauling  required  to  supply  materials 
for  maintenance  must  of  necessity  be  small  in  comparison  with  the 
ordinary  traffic  over  the  road;  and  hence  this  consideration  should 
not  have  undue  weight. 

Attention  should  also  be  given  to  the  disposal  of  the  drainage 


70  KOAD   LOCATION.  [CHAP.   II. 

water,  and  to  the  question  of  danger  from  high  water  in  the  streams. 
For  example,  in  Fig.  7  it  is  possible  to  locate  a  line  on  the  upper  side 
of  the  map  with  an  uniform  grade  of  4  per  cent7  but  such  a  line  will 
lie  so  near  the  branch  entering  the  main  stream  at  B  as  to  be  in 
danger  from  floods.  The  matter  of  crossing  streams  should  receive 
the  most  careful  study.  Bridges  are  comparatively  expensive  to 
build  and  to  maintain. 

It  may  be  cheaper  to  carry  the  road  across  the  gully  on  an  em- 
bankment or  a  trestle  than  to  make  a  detour  around  the  head  of  the 
valley.  This  question  can  be  determined  by  comparing  the  greater 
cost  of  construction  of  the  shorter  line  with  the  capitalized  value 
of  the  greater  cost  of  operating  the  longer  line. 

In  some  localities  the  protection  of  the  road  against  snow  is  an 
important  matter.  Deep  cuts  almost  always  catch  snow;  and  for 
this  reason  it  is  sometimes  better  to  go  around  a  point  by  a  sup- 
ported grade  than  to  cut  through  it.  In  a  snow  country  roads 
should  be  located  on  slopes  facing  south  and  east  in  preference  to 
slopes  facing  north  and  west,  as  the  sun  has  greater  power  on  the 
former  to  melt  the  snow. 

"Nothing  pays  like  first  cost  in  road  building,"  i.  e.,  money  ex- 
pended in  intelligent  study  of  the  location  is  the  most  economical 
expenditure  in  the  construction  of  a  road. 

94.  ESTABLISHING  THE  GRADE  LINE.  After  placing  the  center 
line,  the  topography  should  be  taken  on  each  side  of  the  line  for 
some  distance — the  distance  depending  upon  the  lay  of  the  land; — 
and  then  a  map  should  be  drawn  showing  the  line  and  the  contours. 
This  will  serve  to  show  whether  the  line  is  placed  to  the  best  advan- 
tage, and  whether  any  changes  are  desirable.  This  is  especially 
necessary  over  rough  ground  or  where  the  line  is  on  a  maximum 
grade. 

The  center  line  for  a  final  location  should  be  carefully  run  and 
permanently  marked,  so  that  it  may  be  re-located  if  necessary.  A 
line  of  levels  should  be  run  and  a  profile  drawn,  upon  which  the 
grades  may  be  established  and  from  which  the  earthwork  may  be 
estimated  (see  §  125). 


CHAPTER    III. 
EARTH     ROADS. 

95.  The  earth  road  is  the  cheapest  road  in  first  cost,  and  is  by 
far  the  most  common.  It  is  a  light  traffic  road,  and  only  when  the 
traffic  becomes  considerable  is  it  possible  to  procure  the  money  with 
which  to  improve  the  surface  by  the  use  of  some  foreign  material,  as 
gravel  or  broken  stone.  Fortunately,  the  best  form  for  the  earth 
road  is  also  the  best  preparation  for  any  improved  surface.  This 
surface,  whatever  its  nature,  is  only  a  roof  to  protect  the  earth  from 
the  effects  of  weather  and  travel,  and  any  preparation  that  will 
enable  the  native  soil  when  unprotected  to  resist  these  elements  will 
enable  it  the  better  to  serve  as  a  foundation  for  the  improved  sur- 
face. Because  of  the  importance  of  earth  roads  as  a  means  of  trans- 
portation and  also  because  of  the  importance  of  a  properly  formed 
and  well-drained  road-bed  for  all  improved  road  surfaces,  earth 
roads  will  be  considered  somewhat  fully. 

96.  The  term  earth  road  will  be  used  as  applying  to  roads  whose 
surface  consists  of  the  native  soil,  and,  unless  otherwise  stated,  it 
will  be  understood  as  meaning  a  road  whose  surface  is  loam  or  clay. 
The  Construction  and  Maintenance  of  roads  on  loam  and  clay  will 
be  discussed  in  Art.  1  and  2,  and  roads  on  sand  in  Art.  3. 

Art.  1.     Construction. 

97.  DRAINAGE.  Drainage  is  the  most  important  matter  to  be 
considered  in  the  construction  of  earth  roads,  since  no  road,  whether 
earth  or  stone,  can  long  remain  good  without  it.  Drainage  alone 
will  often  change  a  bad  earth  road  to  a  good  one,  while  the  best 
stone  road  may  be  destroyed  by  the  absence  of  proper  drainage. 
Water  is  the  natural  enemy  of  earth  roads,  for  mixed  with  dirt  it 
makes  mud,  and  mud  makes  bad  going    The  rain  or  snow  softens 

71 


72  EARTH    ROADS.  [CHAP.    III. 

the  earth;  the  horses'  feet  and  the  wagon  wheels  mix  and  knead 
it;  and  soon  the  road  becomes  impassable  mud,  which  the  frost 
finally  freezes,  the  second  state  of  the  road  being  worse  than  the 
first — for  a  time  at  least.  Further,  if  the  water  is  allowed  to  course 
down  the  middle  of  the  road,  it  will  wash  away  the  earth,  and  leave 
gullies  in  the  surface  that  must  be  laboriously  filled  up  by  traffic 
or  repairs.  No  road,  however  well  made  otherwise,  can  endure  if 
water  collects  or  remains  on  it.  Prompt  and  thorough  drainage  is 
a  vital  essential  in  all  road  construction,  and  particularly  so  for 
earth  roads. 

A  perfectly  drained  road  will  have  three  systems  of  drainage, 
each  of  which  must  receive  special  attention  if  the  best  results  are  to 
be  obtained.  This  is  true  whether  the  trackway  be  iron,  broken 
stone,  gravel,  or  earth,  and  it  is  emphatically  true  of  earth.  These 
three  systems  are  underdrainage,  side  ditches,  and  surface  drainage. 

98.  Underdrainage.  Any  soil  in  which  the  standing  water  in 
the  ground  comes  at  any  season  of  the  year  within  4  or  5  feet  of  the 
surface  will  be  benefited  by  drainage;  that  is,  if  the  soil  does  not 
have  a  natural  underdrainage,  it  will  be  improved  for  road  purposes 
by  artificial  subsurface  drainage.  It  is  the  universal  observation 
that  roads  in  low  places  which  are  underdrained  dry  out  sooner  than 
undrained  roads  on  high  land.  Underdrained  roads  never  get  as 
bad  as  do  those  not  so  drained.  Underdrainage  without  grading 
is  better  than  grading  without  drainage;  and,  in  general,  it  may  be 
said  that  there  is  no  way  in  which  road  taxes  can  be  spent  to  better 
advantage  than  in  subsurface  drainage.  Underdrainage  is  the  very 
best  preparation  for  a  gravel  or  stone  road.  Gravel  or  broken 
stone  placed  upon  an  undrained  foundation  is  almost  sure  to  sink 
(perhaps  slowly,  but  none  the  less  surely),  whatever  its  thickness; 
whereas  a  thinner  layer  upon  a  drained  road-bed  will  give  much 
better  service.  Underdrained  roads  without  gravel  are  better  than 
graveled  roads  without  underdrainage. 

99.  The  Object.  The  opinion  is  quite  general  that  the  sole  object 
of  underdrainage  is  to  remove  the  surface  water,  but  this  is  only  a 
small  part  of  the  advantages  of  the  underdrainage  of  roads. 

The  most  important  object  is  to  lower  the  water  level  in  the  soil. 
The  action  of  the  sun  and  the  breeze  will  finally  dry  the  surface  of 
the  road;  but  if  the  foundation  is  soft  and  spongy,  the  wheels  will 


AKT.   1.]  CONSTRUCTION.  73 

wear  ruts  and  the  horses'  feet  will  make  depressions  between  the 
ruts.  The  first  shower  fills  these  depressions  with  water,  and  the 
road  is  soon  a  mass  of  mud.  A  good  road  can  not  be  maintained 
without  a  good  foundation,  and  an  undrained  soil  is  a  poor 
foundation,  while  a  dry  subsoil  can  support  almost  any  load. 

A  second  object  of  underdrainage  is  to  dry  the  ground  quickly 
after  a  freeze.  When  the  frost  comes  out  of  the  ground  in  spring, 
the  thawing  is  quite  as  much  from  the  bottom  as  from  the  top.  If 
the  land  is  underdrained,  the  water  when  released  by  thawing  from 
below  will  be  immediately  carried  away.  This  is  particularly  im- 
portant in  road  drainage,  since  the  foundation  will  then  remain  solid 
and  the  road  itself  will  not  be  cut  up.  Underdrainage  will  usually 
prevent  the  " bottom  dropping  out"  when  the  frost  goes  out  of  the 
ground. 

A  third,  and  sometimes  a  very  important,  object  of  subdrainage 
is  to  remove  what  may  be  called  the  underflow.  In  some  places 
where  the  ground  is  comparatively  dry  when  it  freezes  in  the  fall,  it 
will  be  very  wet  in  the  spring  when  the  frost  comes  out — surpris- 
ingly so  considering  the  dryness  before  freezing.  The  explanation 
is  that  after  the  ground  freezes,  water  rises  slowly  in  the  soil  by 
the  hydrostatic  pressure  of  the  water  in  higher  places;  and  if  it  is 
not  drawn  off  by  underdrainage  it  saturates  the  subsoil  and  rises  as 
the  frost  goes  out,  so  that  the  ground  which  was  comparatively  dry 
when  it  froze  is  practically  saturated  when  it  thaws. 

100.  The  underdrainage  of  a  road  not  only  removes  the  water, 
but  prevents,  or  greatly  reduces,  the  destructive  effect  of  frost. 
The  injurious  effect  of  frost  is  caused  entirely  by  the  presence  of 
water,  and  the  more  water  there  is  in  the  road-bed  the  greater  the 
injury  to  the  road.  The  water  expands*  on  freezing,  the  surface  of 
the  road  is  upheaved,  and  the  soil  is  made  porous;  when  thawing 
takes  place,  the  ground  is  left  honeycombed  and  spongy,  ready  to 
settle  and  sink,  and  under  traffic  the  road  "breaks  up."  If  the 
road  is  kept  dry,  it  will  not  break  up.  Underdrainage  can  not  pre- 
vent the  surface  of  the  road  from  becoming  saturated  with  water 
during  a  rain,  but  it  is  the  best  means  of  removing  the  surplus 
water,  thus  drying  the  surface  and  preventing  the  subsequent  heav- 
ing by  frost. 

That  frost  is  harmless  where  there  is  no  moisture,  is  shown  on  a 


74  EARTH  ROADS.  [CHAP.  III. 

large  scale  in  the  semi-arid  regions  west  of  the  Mississippi  river. 
The  ground  there  is  normally  so  dry  that  during  the  winter,  when 
it  is  frozen,  cracks  form  half  an  inch  or  more  wide,  owing  to  the  dry- 
ing and  consequent  contraction  of  the  soil,  which  shows  that  there 
is  no  expansion  by  the  freezing  of  the  water  in  the  soil;  and  there- 
fore in  this  region  there  is  no  heaving  or  disturbance  by  frost. 
Houses  are  often  built  on  the  very  surface  of  the  ground,  and  no 
trouble  is  ever  experienced  by  the  action  of  frost. 

101.  The  Tile.  The  best  and  cheapest  method  of  securing  under- 
drainage  is  to  lay  a  line  of  porous  or  farm  tile  3  or  4  feet  deep  on  one 
or  both  sides  of  the  roadway.  The  ordinary  farm  tile  is  entirely 
satisfactory  for  road  drainage.  It  should  be  uniformly  burned, 
straight,  round  in  cross  section,  smooth  inside,  and  have  the  ends 
cut  off  square.  Tile  may  be  had  from  3  to  30  inches  in  diameter 
The  smaller  sizes  are  usually  a  little  over  a  foot  long, — the  excess 
length  being  designed  to  compensate  for  breakage;  and  the  larger 
sizes  are  nominally  2  or  2\  feet  long,  but  usually  a  little  longer.  The 
cost  of  tile  free  on  board  at  the  factory  is  usually  about  as  in  Table 
13,  page  75.  Y's  for  connections  can  be  had  at  most  factories,  but 
they  cost  four  or  five  times  as  much  as  an  ordinary  tile.  With 
patience  and  a  little  experience  ordinary  tile  can  be  cut  to  make 
fairly  good  connections. 

Before  the  introduction  of  tile  for  agricultural  drainage,  it  was 
customary  to  secure  underdrainage  by  digging  a  trench  and  deposit- 
ing in  the  bottom  of  it  logs  or  bundles  of  brush,  or  a  layer  of  broken 
stone;  or  a  channel  for  the  water  was  formed  by  setting  a  line  of 
stones  on  each  side  of  the  trench  and  joining  the  two  with  a  third 
line  resting  on  these  two.  Apparently  it  is  still  the  practice  in  some 
localities  to  use  such  substitutes  for  ordinary  drain  tile.  Tiles  are 
better,  since  they  are  more  easily  laid  and  are  less  liable  to  get 
clogged.  Tiles  are  cheaper  in  first  cost,  even  when  shipped  consid- 
erable distances  by  rail,  than  any  reasonably  good  substitute,  and 
the  drains  are  much  more  durable. 

Tiles  are  laid  simply  with  their  ends  in  contact,  care  being  taken 
to  turn  them  until  the  ends  fit  reasonably  close.  In  some  localities 
there  is  apparently  fear  that  the  tile  will  become  stopped  by  fine 
particles  of  soil  entering  at  the  joints,  and  consequently  it  is  specified 
that  the  joint  shall  be  covered  with  tarred  paper  or  something  of  the 


ART.   1.] 


CONSTRUCTION. 


75 


sort ;  but  in  the  Mississippi  Valley,  where  immense  quantities  of  tile 
have  been  laid,  no  such  difficulty  has  been  encountered.  With  a 
very  slight  fall  or  even  no  fall  at  all,  tiles  will  keep  clean,  if  a  free 
outlet  is  provided,  and  they  are  not  obstructed  by  roots  of  trees — 
particularly  willow. 

In  some  localities  it  is  apparently  customary  to  use  collars 
around  the  ends  of  the  tile  to  keep  them  in  line.  If  the  bottom  of 
the  trench  is  made  but  little  wider  than  the  diameter  of  the  tile,  or 
if  a  groove  is  scooped  out  in  the  bottom  of  the  trench  to  fit  the  tile, 
no  difficulty  need  be  apprehended  from  this  source. 


TABLE  13. 
Cost  and  Weight  of  Drain  Tile. 


Inside 

Price  per  1000, 

Weight 

Number  of  Feet 

Diameter. 

f.  o.  b.  Factory. 

per  Foot. 

in  a  Car  Load. 

3  inches 

$10.00 

5  1b. 

7  000 

4      " 

15.00 

7  " 

6  500 

5      " 

20.00 

9  " 

5  000 

6      " 

27.00 

12  " 

4  000 

7      " 

35.00 

14  " 

3  000 

8      " 

45.00 

18  " 

2  500 

9      " 

55.00 

21   " 

1800 

10      " 

65.00 

25  " 

1600 

12      " 

90.00 

33  " 

1000 

14      " 

120.00 

43  " 

800 

16      " 

150.00 

50  " 

600 

18      " 

240.00 

70  " 

400 

20      " 

300.00 

83  " 

330 

24      " 

360.00 

112   " 

300 

102.  The  Fall.  There  is  no  danger  of  the  grade  of  the  tile  being 
too  great,  and  the  only  problem  is  to  secure  sufficient  fall.  A  num- 
ber of  authorities  on  farm  drainage  and  also  several  engineering 
manuals  assert  that  a  fall  of  2\  or  3  inches  per  100  feet  is  the  lowest 
limit  that  should  be  attempted  under  the  most  favorable  conditions; 
but  practical  experience  has  abundantly  proved  that  a  much  smaller 
fall  will  give  good  drainage.  In  central  Illinois  and  northern 
Indiana  are  many  lines  of  tile  having  falls  of  only  J  to  }  of  an  inch 
per  100  feet  which  are  giving  satisfactory  drainage;  and  not  un- 
frequently  the  ordinary  porous  tiles  laid  absolutely  level  directly 
upon  the  earth  in  the  bottom  of  the  trench,  without  collars  or  other 
covering  over  the  joints,  have  given  good  drainage  without  trouble 


76  EARTH    ROADS.  [CHAP.   III. 

from  the  deposit  of  sediment.  Of  course,  extremely  flat  grades  are 
less  desirable  than  steeper  ones,  since  larger  tiles  must  be  used,  and 
greater  care  must  be  exercised  in  laying  them,  and  there  is  more 
risk  of  the  drain  becoming  obstructed;  but  these  extremely  flat 
grades  are  sometimes  all  that  can  be  obtained,  and  such  drains 
abundantly  justify  the  expense  of  their  construction. 

If  possible  at  reasonable  expense,  the  grade  should  be  at  least 
2  inches  per  100  feet;  and  should  never  be  less  than  \  inch  per  100 
feet  unless  absolutely  necessary.  On  level  or  nearly  level  ground, 
the  fall  may  be  increased  by  laying  the  tile  at  the  upper  end  shallower 
than  at  the  lower. 

103.  Size  of  Tile.  The  following  formula  has  frequently  been 
employed  to  determine  the  size  of  tile: 

Q  =  39.25>J[d5,   ........     (1) 

in  which  Q  is  the  discharge  in  cubic  feet  per  second,  /  the  fall  in  a 
distance  I  (both  in  feet),  and  D  the  inside  diameter  of  the  tile  in 
feet.  The  above  formula  may  be  reduced  to  the  following  more 
useful  form: 

V  =  6,798yjld% (2) 

in  which  V  is  the  discharge  in  cubic  feet  per  24  hours,  and  d  is  the 
diameter  of  the  tile  in  inches.  Water  1  inch  deep  over  an  acre  of 
land  amounts  to  3,630  cubic  feet;  and  therefore  if  we  divide  the 
constant  in  equation  (2)  by  3,630,  we  get  the  following  formula: 

A  =  l$^Td\ (3) 

in  which  A  is  the  number  of  acres  for  which  a  tile  having  a  diameter 
of  d  inches  and  a  fall  of  /  feet  in  a  length  of  I  feet  will  remove  1  inch 
in  depth  of  water  in  24  hours. 

Equation  (1)  is  the  formula  ordinarily  employed  for  the  flow  of 
water  through  smooth  cast-iron  pipe,  and  is  only  roughly  applicable 
to  tile.  It  probably  gives  too  great  a  capacity  for  tile.  However, 
all  the  factors  of  the  problem  are  too  uncertain  to  justify  an  attempt 
at  mathematical  accuracy.  For  example,  we  can  not  know  with 
any  certainty  the  maximum  rate  of  rainfall,  the  duration  of  the 


ART.    l.J  CONSTRUCTION.  77 

maximum  rate,  the  permeability  of  the  soil,  the  amount  of  water 
retained  by  the  soil,  the  effect  of  surface  water  flowing  onto  the 
road  from  higher  ground,  the  area  to  be  drained,  etc.  The  above 
formula  is  useful  only  in  a  locality  where  there  is  no  local  experience 
with  tile ;  and  its  chief  value  consists  in  showing  the  relation  between 
capacity  and  grade,  and  the  effect  of  a  variation  in  the  diameter  of 
the  tile. 

The  object  of  underdraining  a  road  is  to  prevent  the  plane 
of  saturation  from  rising  so  near  the  surface  as  to  soften  the 
foundation  of  the  road  even  during  a  wet  time,  and  therefore  the 
provision  for  underdrainage  should  be  liberal;  but  what  will  be 
adequate  in  any  particular  case  depends  upon  the  amount  of  traffic, 
the  local  conditions,  the  soil,  etc.  The  best  practice  in  agricultural 
drainage  provides  for  the  removal  of  0.5  to  1  inch  of  water  per  day; 
but  since  the  side  ditches  will  assist  in  removing  rain  water  from  the 
road,  it  is  probable  that  a  provision  for  the  removal  of  half  an  inch 
per  day  is  sufficient  for  the  underdrainage  of  a  road.  If  there  is  an 
underflow  of  water  from  higher  ground,  or  if  the  ground  is  "  springy," 
then  the  ordinary  provisions  for  underdrainage  should  be  increased. 

104.  It  is  not  wise  to  lay  a  smaller  tile  than  a  4-inch  one,  and 
probably  not  smaller  than  a  5-inch.  Tiles  can  not  be  laid  in  exact 
line,  and  any  tilting  up  of  one  end  reduces  the  cross  section.  Again, 
if  there  is  a  sag  in  the  line  equal  to  the  inside  diameter,  the  tile  will 
shortly  become  entirely  stopped  by  the  deposit  of  silt  in  the  de- 
pression. 

It  is  sometimes  wiser  to  lay  a  larger  tile  than  to  increase  the  fall. 
Again,  it  may  be  better  to  lay  a  large  tile  near  the  surface  with 
smaller  fall  than  to  lay  small  tile  deeper  with  a  greater  fall. 
Ordinarily,  the  deeper  the  tile  the  better  the  drainage,  although  3^ 
or  4  feet  deep  is  usually  sufficient. 

105.  Laying  the  Tile.  It  is  unwise  to  enter  upon  any  detailed 
discussion  of  the  art  of  laying  the  tile.  The  individual  tiles  should 
be  laid  in  line  both  vertically  and  horizontally,  with  as  small  joints 
at  the  end  as  practicable.  Care  should  also  be  taken  that  the  tile 
is  laid  to  a  true  grade,  particularly  if  the  fall  is  small,  for  if  there  is 
a  sag  it  will  become  filled  with  sediment,  or  if  there  is  a  crest  silt 
will  be  deposited  just  above  it.  The  drain  should  have  a  free  and 
adequate  outlet.     The  end  of  the  line  of  tile  should  be  protected 


78  EARTH    ROADS.  [CHAP.   III. 

by  masonry,  by  plank  nailed  to  posts,  or  by  replacing  three  or 
four  tiles  at  the  lower  end  by  an  iron  pipe  or  by  a  wooden  box. 

106.  Cost  of  Laying  Tile.  The  prevailing  prices  for  laying  tile 
in  loam  with  clay  subsoil  is  about  as  follows:  for  8-inch  tile  or  less 
10  cents  per  rod  for  each  foot  of  depth;  for  9-inch,  11  cents;  for 
12-inch,  14  cents;  for  15-inch,  17  cents;  and  for  16-inch,  18  cents. 
To  aid  in  remembering  the  above  data,  notice  that  the  price  is  10 
cents  per  rod  per  foot  of  depth  for  8-inch  tile  or  less,  with  an  in- 
crease of  1  cent  for  each  additional  inch  of  diameter. 

The  cost  of  a  mile  of  5-inch  tile  drain  is  usually  from  $200  to 
$250,  exclusive  of  freight  on  the  tile.  If  there  is  any  considerable 
amount  of  work,  the  above  prices  for  the  smaller  tile  can  be  reduced 
10  to  20  per  cent;  and  often  there  is  enough  discount  on  the  prices 
given  in  Table  13,  page  75,  to  cover  the  railroad  freight-charges. 
A  tile  drain  is  a  permanent  improvement  with  no  expense  for  main- 
tenance, the  benefit  being  immediate  and  certain;  and  therefore  it 
is  doubtful  if  money  can  be  spent  on  earth  roads  to  better  advan- 
tage than  in  laying  tile. 

107.  One  vs.  Two  Lines.  Usually  a  line  of  tile  2\  to  3  feet  ieep 
under  the  ditch  at  one  side  of  the  road  will  give  sufficient  drainage. 
Some  tests  made  by  the  Illinois  Agricultural  Experiment  Station 
(not  yet  published)  seem  to  indicate  that  one  line  will  give  fairly 
good  drainage  under  the  most  adverse  conditions.  The  experiment 
consisted  in  the  drainage  of  a  piece  of  land  selected  as  the  worst 
that  could  be  found  in  a  part  of  the  state  notorious  as  having  a  large 
area  of  hard-pan  which  it  was  generally  considered  could  not  be 
underdrained  "  because  the  soil  held  water  like  a  jug."  Lines  of  tile 
were  laid  2\  feet  deep  and  50  feet  apart.  The  water  level  at  a  point- 
midway  between  the  lines  of  tiles  was  lowered  18  inches,  when  at 
the  same  time  the  water  level  in  the  undrained  portion  of  the  field 
was  only  6  inches  below  the  surface.  In  this  case  the  surface  oi  the 
ground  water  had  a  slope  of  1  foot  in  25  feet. 

A  few  other  observations  seem  to  confirm  the  above  result  for  <he 
slope  of  the  surface  of  saturation.  The  exact  form  of  the  surface 
of  saturation  is  not  known,  but  it  is  known  to  be  a  curve  slightly 
convex  upward.  The  inclination  varies  with  the  nature  of  the  soil, 
is  most  convex  near  the  tile,  and  is  most  convex  immediately  after 
a  rain  and  gradually  thereafter  approaches  an  inclined  plane. 


AKT.   1.]  CONSTRUCTION.  79 

The  traveled  portion  is  usually  not  more  than  50  feet  wide,  and 
therefore  a  single  line  of  tile  2-i-  to  3  feet  below  the  bottom  of  the 
side  ditch,  if  of  adequate  size,  will  give  nearly  perfect  drainage;  and 
a  second  line  will  not  materially  improve  it.     For  example,  in  Fig.  8, 


Fjg.  8. 

if  A  represents  the  first  line  of  tile,  the  surface  of  the  ground  water 
is  represented  by  the  lines  ABC.  If  a  second  line  of  tile,  D,  is  laid, 
the  water  surface  will  be  A  B  D,  and  the  second  line  will  drain  only 
the  comparatively  small  portion  C  B  D.  The  diagram  shows  that 
a  single  line  well  below  the  surface  is  far  better  than  two  shallow 
ones.  For  example,  lowering  the  tile  A  6  inches,  lowers  the  water 
surface  to  A'  C ,  which  represents  better  drainage  than  the  line 
A  B  D  with  the  two  lines  of  tile. , 

It  is  generally  conceded  that  for  agricultural  drainage  it  is  suffi- 
cient to  place  the  lines  of  tile  100  feet  apart,  provided  they  are 
of  reasonable  size  and  at  sufficient  depth.  A  tile  will  give  agricul- 
tural drainage  50  feet  on  either  side  of  it;  that  is,  a  tile  under  only 
one  side  ditch  will  give  agricultural  drainage  of  the  traveled  way. 
More  thorough  drainage  is  required  for  agricultural  than  for  road 
purposes,  since  wrhen  damp  most  soils  will  pack,  which  is  harmful 
to  agricultural  land  but  beneficial  to  a  road. 

108.  The  above  seems  to  prove  that  one  line  of  tile,  if  of  proper 
size  and  at  sufficient  depth,  will  afford  sufficient  drainage  for  road 
purposes;  but  nevertheless  it  is  claimed  by  competent  authorities 
that  two  lines  are  sometimes  required.  In  some  localities  a  stratum 
of  hard-pan  near  the  surface  makes  it  necessary  to  lay  the  tile  so 
shallow  that  two  lines  are  really  required;  and  sometimes  the  tile 
is  so  small  or  so  poorly  laid  that  one  line  is  insufficient. 

In  case  of  doubt  as  to  whether  one  or  two  lines  of  tile  are 
needed,  put  in  one  and  watch  the  results.  If  both  sides  of  the 
road  are  equally  good,  another  tile  drain  is  not  needed.     In  mak- 


80  EARTH    ROADS.  [CHAP.   III. 

ing  these  observations  care  should  be  taken  not  to  overlook  any  of 
the  factors,  as,  for  example,  the  difference  in  the. effect  of  the  sun 
upon  the  south  and  the  north  sides'  of  vthe  road,  the  effect  of  shade 
or  of  seepage  water,  the  transverse  slopes  of  the  surface  of  the  road, 
etc. 

109.  Location  of  Tile.  Some  writers  on  roads  recommend  a 
line  of  tile  under  the  middle  of  the  traveled  portion.  A  tile 
under  the  middle  of  the  road  is  a  little  more  effective  than  one 
at  the  same  level  under  the  side  ditch;  but  the  former  is  con- 
siderably more  expensive  to  lay,  since  it  necessitates  more  digging — 
whether  the  tile  is  laid  before  or  after  the  road  is  graded.  With  the 
same  depth  of  digging,  a  tile  under*  the  side  ditch  is  more  effective 
than  one  under  the  center  of  the  road.  Further,  if  the  tile  is  under 
the  center,  there  is  liability  of  the  settling  of  the  soil  in  the  trench, 
which  will  make  a  depression  and  probably  a  mud  hole;  and  if  the 
tile  becomes  stopped,  it  is  expensive  to  dig  it  up,  and  the  doing  so 
interferes  with  traffic  Finally,  if  the  road  is  ever  graveled  or 
macadamized,  the  disadvantage  of  having  the  tile  drain  under  the 
center  of  the  road  is  materially  increased. 

Some  writers  advocate  the  use  of  a  line  of  tile  near  the  surface, 
on  each  side  of  the  trackway.  The  object  of  placing  the  tile  in  this 
position  is  to  secure  a  rapid  drainage  of  the  surface;  but  very  little, 
if  any,  water  from  the  surface  will  ever  reach  a  tile  so  placed,  since 
the  road  surface  when  wet  is  puddled  by  the  traffic,  which  pre- 
vents the  water  percolating  through  the  soil.  It  is  certain  that 
in  clay  or  loam  the  drainage  thus  obtained  is  of  no  practical  value. 
Many  farmers  have  tried  to  drain  their  barns-yard  by  laying  tile 
near  the  surface,  but  always  without  appreciable  effect.  The 
deeper  the  tile  the  better  the  drainage. 

One  writer  advocates  digging  a  trench  in  the  middle  of  the  road 
and  filling  it  nearly  full  with  broken  stone  or  poles,  and  then  filling 
the  remainder  with  earth.  This  drain  is  to  be  connected  with  both 
side  ditches  by  cross  drains  50  feet  apart.  Such  construction  would 
be  very  expensive  and  practically  useless. 

The  rapid  surface  drainage  sought  by  putting  a  tile  or  its  equiva- 
lent near  the  surface,  can  best  be  secured  by  giving  the  surface  of 
the  road  a  proper  crown  and  keeping  it  free  from  ruts  and  holes 
(see  §  194). 


ART.   1.]  CONSTRUCTION.  81 

While  a  line  of  tile  on  one  side  of  the  road  is  usually  sufficient, 
there  is  often  a  great  difference  as  to  the  side  on  which  it  should  be 
laid.  If  one  side  of  the  road  is  higher  than  the  other,  the  tile  should 
be  on  the  high  side  to  intercept  the  ground  water  flowing  down  the 
slope  under  the  surface.  Sometimes  a  piece  of  road  is  wet  because 
of  a  spring  in  the  vicinity,  or  perhaps  the  road  is  muddy  because 
of  a  stratum  which  brings  the  water  to  the  road  from  higher  ground ; 
in  either  case,  the  source  of  supply  should  be  tapped  with  a  line 
of  tile  instead  of  trying  to  improve  the  road  by  piling  up  earth. 

110.  Side  Ditches.  The  side  ditches  are  to  receive  the  water 
from  the  surface  of  the  traveled  way,  and  should  carry  it  rapidly  and 
entirely  away  from  the  roadside.  They  are  useful,  also,  to  inter- 
cept and  carry  off  water  that  would  otherwise  flow  from  the  side 
hills  upon  the  road.  Ordinarily  they  need  not  be  deep;  but,  if 
possible,  should  have  a  broad,  flaring  side  toward  the  traveled  way, 
to  prevent  accident  if  a  vehicle  should  be  crowded  to  the  extreme 
side  of  the  roadway.  The  outside  bank  should  be  flat  enough  to 
prevent  caving. 

If  the  road  is  tiled  as  above  recommended,  the  side  ditch  need 
not  be  very  large;  but  it  should  be  of  such  a  form  as  to  permit  its 
construction  with  the  road  machine  or  scraping  grader  (§  142)  or 
with  a  drag  scraper  (§  137),  instead  of  requiring  to  be  made  by  hand. 
On  comparatively  level  ground,  the  proper  form  of  side  ditch  is 
readily  and  cheaply  made  with  the  usual  road  machine.  Fig.  9, 
page  85,  shows  a  shallow  ditch  of  the  proper  form;  and  Fig.  10 
shows  a  deeper  one  of  the  same  general  form.  If  a  larger  ditch  is 
needed,  it  should  be  of  such  a  form  as  to  be  made  chiefly  with  the 
drag-scoop  scraper. 

A  deep  narrow  ditch  is  also  expensive  to  maintain,  since  it  is 
easily  obstructed  by  the  caving  banks,  by  weeds,  and  by  floating 
trash.  Fortunately  the  shallow  ditch  is  easy  and  cheap  to  construct 
and  also  to  maintain.  If  it  is  necessary  to  carry  water  along  the 
side  of  the  road  through  a  rise  in  the  ground,  it  is  much  better  to  lay 
a  line  of  tile  and  nearly  fill  the  ditch  than  to  attempt  to  maintain  a 
narrow  deep  ditch.  A  tile  is  much  more  effective  per  unit  of  cross 
section  than  most  open  ditches. 

111.  The  side  ditch  should  have  a  uniform  grade  and  a  free  out- 
let into  some  stream,  so  as  to  carry  the  water  entirely  away  from 


82  EARTH    ROADS.  [CHAP.   III. 

the  road.  No  good  road  can  be  obtained  with  side  ditches  that 
hold  the  water  until  it  evaporates.  Much  ostensible  road  work 
is  a  positive  damage  for  this  reason.  Piling  up  the  earth  in  the 
middle  of  the  road  is  perhaps  in  itself  well  enough,  but  leaving 
undrained  holes  at  the  side  probably  more  than  counterbalances 
the  benefits  of  the  embankment.  A  road  between  long  artificial 
ponds  is  always  inferior  and  is  often  impassable.  It  is  cheaper  and 
better  to  make  a  lower  embankment,  and  to  drain  thoroughly  the 
holes  at  the  side  of  the  road.  Public  funds  can  often  be  more 
wisely  used  in  making  ditches  in  adjoining  private  lands  than  in 
making  ponds  at  the  roadside  in  an  attempt  to  improve  the  road 
by  raising  the  surface.  It  is  cheaper  and  better  to  allow  the  water 
to  run  away  from  the  road  than  to  try  to  lift  the  road  out  of  the 
water. 

When  the  road  is  in  an  excavation,  great  care  should  be  taken 
that  a  ditch  is  provided  on  each  side  to  carry  away  the  water  so  that 
it  shall  not  run  down  the  middle  of  the  road.  Every  road  should 
have  side  ditches,  even  one  that  runs  straight  down  the  side  of  a 
hill.  Indeed,  the  steepest  road  needs  the  side  ditch  most,  although 
it  often  has  none.  Frequently  the  water  runs  down  the  middle  of 
the  road  on  a  side  hill  and  wears  it  into  gullies,  which  are  a  discom- 
fort, and  often  dangerous,  in  both  wet  weather  and  dry. 

In  a  slightly  rolling  country,  the  side  ditch  frequently  has  no 
outlet,  and  the  water  is  allowed  to  accumulate  at  the  foot  of  the 
slope  and  there  remain  until  it  is  absorbed  by  the  ground  or  seeps 
into  a  tile  drain.  The  difficulty  could  be  remedied  by  providing  an 
inlet  from  the  open  ditch  to  the  tile.  This  may  be  a  well,  walled 
with  plank  or  masonry  without  mortar  (except  near  the  top)  and 
having  a  grating  in  the  side  or  top  through  which  the  water  may 
pass.  The  well  should  be  large  enough  to  allow  a  man  to  enter  it  to 
clean  it,  and  should  extend  a  foot  or  more  below  the  bottom  of  the 
tile.  Earth  roads  in  villages  and  towns  are  usually  better  provided 
with  such  inlets  than  country  roads,  but  both  could  be  materially 
improved  at  comparatively  small  expense  by  attention  to  this 
matter. 

112.  If  it  can  be  prevented,  no  attempt  should  be  made  to  carry 
water  long  distances  in  side  ditches;  for  large  bodies  of  water  are 
hard  to  handle,  and  are  liable  to  become  very  destructive.     Side 


AM.   1.]  CONSTRUCTION.  83 

ditches  should  discharge  frequently  into  the  natural  watercourses, 
though  to  compass  this,  it  may  in  some  cases  be  necessary  to  carry 
the  water  from  the  high  side  to  the  low  side  of  the  road.  This  is 
sometimes  done  by  digging  a  gutter  or  by  building  a  dam  diagonally 
across  the  road,  but  both  are  very  objectionable.  A  better  way 
is  to  lay  a  tile  or  put  in  a  culvert  (see  Fig.  55,  page  210),  the  amount 
of  water  determining  which  shall  be  done. 

It  is  sometimes  necessary  to  carry  water  a  considerable  distance 
in  the  side  ditches,  as,  for  example,  when  the  road  is  in  excavation. 
This  requires  deep  ditches,  which  are  undesirable  and  dangerous; 
and  if  the  grade  is  considerable,  the  ditches  wash  rapidly.  In  such 
cases,  it  is  wise  to  lay  a  line  of  tile  under  the  side  ditch,  and  turn  the 
water  from  the  surface  ditch  into  the  tile  drain  at  intervals.  This 
can  be  accomplished  readily  by  inserting  in  the  line  of  porous  tile  a 
Y  section  of  vitrified  sewer  pipe,  with  the  short  arm  opening  up  hill. 
Of  course,  the  short  arm,  i.  e.,  the  vertical  arm,  need  not  be  as  large 
as  the  body.  If  necessary,  two  or  three  lengths  of  porous  tile  may 
be  added  at  the  upper  end  of  the  Y  to  make  connection  with  the 
bottom  of  the  open  ditch.  Earth,  sods,  or  stones  can  be  piled 
around  the  upper  end  of  the  tile  to  make  a  dam  and  to  hold  the  tile 
in  place. 

Some  road  engineers  lay  a  line  of  tile  under  the  side  ditch,  and 
fill  the  trench  with  broken  stone,  thus  making  the  tile  carry  both 
the  surface  water  and  the  underdrainage.  This  practice  probably 
affords  better  surface  drainage,  but  it  costs  more  than  to  allow  the 
surface  water  to  flow  away  in  the  side  ditches.  This  construction 
is  sometimes  defended  on  the  ground  that  the  broken  stone  prevents 
the  wheels  from  striking  the  tile  when  vehicles  are  forced  into  the 
ditches  in  passing.  This  danger  does  not  seem  very  great,  and 
would  not  occur  at  all  if  the  tile  were  laid  at  the  proper  depth ;  but 
this  is  sometimes  impossible  owing  to  a  hard  substratum. 

113.  As  a  rule  side  ditches  will  not  have  too  much  fall,  but 
sometimes  a  ditch  straight  down  a  hill  will  have  so  much  as  to  wash 
rapidly,  in  which  case  it  is  an  advantage  to  put  in  an  obstruction  of 
stone  or  brush.  In  extreme  cases  the  bottom  of  the  ditch  is  paved 
with  stones. 

114.  Surface  Drainage.  The  drainage  of  the  surface  of  a  road 
is  very  important,  and  is  provided  for  by  making  the  surface  crown- 


84  EARTH  ROADS.  [CHAP.  III. 

ing  and  keeping  it  smooth.  It  should  be  remembered  that  water 
upon  the  surface  of  the  road  can  not  be  carried  away  by  the  under- 
drains,  since  the  water  can  reach  them  only  after  it  has  penetrated 
and  softened  the  road  surface.  The  slope  from  the  center  to  the 
side  should  be  enough  to  carry  the  water  freely  and  quickly  to  the 
side  ditch;  and  if  the  surface  is  kept  free  from  ruts  and  holes,  less 
crown  will  suffice  than  if  no  attention  is  given  to  keeping  the  surface 
smooth.  If  there  is  not  enough  crown,  the  water  can  not  easily 
reach  the  side  ditches;  and  hence  the  road  soon  becomes  water- 
soaked. 

On  the  other  hand,  the  crown  may  be  too  great.  If  the  side 
slopes  are  so  steep  that  traffic  keeps  continually  in  the  middle,  the 
road  will  be  worn  hollow  and  retain  the  water  instead  of  shedding  it 
promptly  to  the  side  ditches.  If  the  crown  is  too  great,  it  is  difficult 
for  vehicles  to  turn  out  in  passing  each  other.  Again,  if  the  earth 
is  piled  too  high  in  the  middle,  the  side  slopes  will  be  washed  into 
the  side  ditches,  which  not  only  damages  the  road  but  also  fills  up 
the  ditches.  Further,  if  the  side  slopes  are  steep,  the  top  of  the 
wheel  will  be  farther  from  the  center  of  the  road  than  the  bottom, 
and  the  mud  picked  up  by  the  bottom  of  the  wheel  will  be  carried  to 
the  top  of  the  wheel  and  then  dropped  farther  from  the  centei  of  the 
road  than  it  was  before,  each  vehicle  acting  like  a  plow  and  moving 
the  earth  from  the  center  toward  the  side  of  the  road.  With  the 
ordinary  method  of  caring  for  earth  roads,  more  water  stands  on  a 
very  convex  road  than  on  a  flatter  one. 

The  slope  from  the  center  to  the  side  should  be  at  least  half  an 
inch  to  a  foot,  or  1  foot  in  24  feet;  and  it  should  not  be  more  than  1 
inch  to  a  foot,  or  1  foot  in  12  feet.  If  the  surface  is  well  cared  for, 
the  former  is  better  than  the  latter;  but  in  no  case  is  it  wise  to  ex- 
ceed the  latter  slope. 

There  is  considerable  difference  of  opinion  as  to  the  exact  form 
to  be  given  to  the  surface  of  a  roadway  (see  §  308-12).  Some  claim 
that  it  should  be  the  arc  of  a  circle,  and  others  that  it  should  consist 
of  two  planes  meeting  at  the  center  and  having  their  junction 
rounded  off  with  a  short  curve.  The  first  form  is  shown  in  Fig.  9 
and  the  second  in  Fig.  10.  Great  refinement  in  this  matter  is  neither 
possible  nor  important.  The  proper  crown  can  be  easily  and  cheaply 
constructed  with  the  road  machine  or  scraping  grader  (§  142). 


ART.   1.]  CONSTRUCTION".  85 

The  drainage  of  the  surface  of  a  road  is  chiefly  a  matter  of  main- 
tenance (see  Art.  2  of  the  present  chapter);  and  one  of  the  most 
common  defects  of  maintenance  is  the  failure  to  fill  the  ruts  and 
keep  the  surface  smooth  so  that  the  water  will  be  promptly  dis- 
charged into  the  side  ditches.     A  comparatively  shallow  rut  will 

I- 6ft. +&+ 7fr.6in.  -  -  *♦«  - -  16ft. 


Fig.  9.— Road  Surface  an  Arc.     Shallow  Side  Ditch. 

nullify  the  effect  of  any  reasonable  amount  of  crown,  and  wear 
deeper  and  deeper  with  each  passing  vehicle.  Seldom  is  a  mile  of 
road  seen  which  does  not  have  a  number  of  ruts  and  saucer-like 
depressions  which  catch  and  hold  the  water.  On  undulating  roads, 
ruts  and  holes  are  naturally  drained;  and  this  is  the  reason  why 
undulating  roads  are  better  than  perfectly  flat  ones  (see  Minimum 
Grade,  §  86). 

»— - 6A---f  3/fc-«r 9ft. 7- 15ft. -  9 

Fig.  10.— Road  Surface  an  Arc.    Deeper  Side  Ditch. 

115.  The  crown  should  be  greater  on  steep  grades  than  on  the 
more  level  portions,  since  on  the  grade  the  line  of  steepest  descent  is 
not  perpendicular  to  the  length  of  the  road,  and  consequently  the 
water  in  getting  from  the  center  of  the  road  to  the  side  ditches  travels 
obliquely  down  the  road.  If  the  water  once  commences  to  run 
down  the  center  of  the  roadway  on  a  steep  grade,  the  wheel  tracks 
are  quickly  deepened,  stones  are  loosened  or  uncovered,  and  the  road 
becomes  rough  and  even  dangerous.  Under  these  circumstances, 
it  is  necessary  to  construct  catch-waters,  "water-breaks,"  "hum- 
mocks," or  "  thank-you-marms "  at  intervals  to  catch  the  water 
which  runs  longitudinally  down  the  road,  and  convey  it  to  the 
side  ditches,  thereby  preventing  the  formation  of  gullies  in  the 
road  surface.  These  catch-waters  may  be  either  broad  shallow 
ditches  or  low  flat  ridges  constructed  across  the  road;  and  they 
may  slope  toward  one  or  both  side  ditches.  In  the  former  case,  they 
should  cross  the  road  diagonally  in  a  straight  line;  and  in  the  latter 


SQ 


EAKTH    ROADS. 


[CHAP,  hi. 


case,  in  plan  they  should  be  a  broad  angle  with  the  apex  at  the 
center  of  the  road  pointing  up  hill.  There  is  little  or  no  difference 
between  the  merits  of  the  ditch  and  the  ridge,  unless  the  bottom  of 
the  former  is  paved  with  gravel,  broken  stone,  or  cobbles.  The 
ridges  are  more  common,  but  usually  are  so  narrow  and  so  high  as 
to  form  a  serious  obstruction  to  traffic.  However,  neither  the 
ditches  nor  the  ridges  should  be  used  except  on  steep  grades  where 
really  necessary,  since  either  form  is  at  best  an  obstruction  to  travel. 
The  angle  that  the  catch-waters  shall  have  with  the  axis  of  the  road 
should  be  governed  by  the  steepness  of  the  grade — the  steeper  the 
grade  the  more  nearly  should  the  catch-waters  run  down  the  road. 
They  should  have  a  considerable  breadth  so  that  wheels  may  easily 
ascend  them  and  horses  will  not  stumble  over  them. 

Catch-waters  should  also  be  constructed  in  a  depression  where 
an  ascending  and  a  descending  grade  meet,  in  order  that  they  may 
collect  the  water  that  runs  down  the  traveled  way  and  convey  it 
into  the  side  ditches.  These  catch-waters  should  run  square  across 
the  road,  and  should  be  quite  shallow  ditches,  the  bottom  of  which 
is  hardened  with  gravel,  broken  stone,  or  cobbles. 

116.  Some  writers  recommend  that  a  surface  of  the  road  on  the 
face  of  hillsides  should  consist  of  a  single  slope  inclining  inwards 
(see  Fig.  11).     This  form  of  surface  is  advisable  on  sharp  curves,  but 


Slope  I  in BO  ^"" 


Fig.  11.— Improper  Cross  Section  of  Roa.d  on  Side  Hill. 


is  of  doubtful  propriety  elsewhere.  The  only  advantage  of  this 
form  is  that  the  water  from  the  road  is  prevented  from  flowing  down 
the  outer  face  of  the  embankment;  but  the  amount  of  rain  water 
falling  upon  one  half  of  the  road  can  not  have  a  very  serious  effect 
upon  the  side  of  the  embankment.  With  a  roadway  raised  in  the 
center  and  the  water  draining  off  to  either  side,  the  drainage  will  be 


ART.   1.]  CONSTRUCTION.  8? 

more  effectual  and  speedy  than  if  the  drainage  of  the  outer  half 
must  pass  over  the  inner  half.  If  the  surface  is  formed  of  one  plane, 
as  in  Fig.  11,  the  lower  half  of  it  will  receive  the  greater  share  of  the 
travel;  and  as  it  will  be  more  poorly  drained,  it  is  nearly  certain 
to  wear  hollow.  This  will  interfere  with  the  surface  drainage;  and 
consequently  a  road  with  this  section  will  require  excessive  attention 
to  keep  it  in  good  condition.  Figs.  55  and  56,  page  210,  show  two 
forms  of  Swiss  hillside  roads  having  the  center  higher  than  either 
side. 

Whatever  the  form  of  the  road  surface,  if  the  hillside  is  steep 
there  should  be  a  catch-water  above  the  road  to  prevent  the  water 
from  the  hillside  above  from  flowing  down  on  the  road.  Fig.  11 
shows  such  a  catch- water.  It  should  be,  say,  6  feet  back  from  the 
excavation,  and  should  have  a  width  and  depth  according  to  the 
amount  of  water  to  be  intercepted. 

117.  WIDTH  OF  WHEELWAY.  The  width  of  the  right  of  way- 
varies  greatly,  but  is  usually  between  40  and  66  feet  (see  §  88)- 
With  a  66-foot  right  of  way  it  is  customary  to  reserve  about  6  feet 
outside  of  the  ditch  on  each  side  for  a  foot-way,  and  grade  up  the 
remaining  54  feet.  With  a  40-foot  right  of  way  it  is  customary 
to  reserve  6  feet  on  each  side  for  foot-ways,  thus  leaving  28  feet 
for  ditches  and  wheel-ways.  For  equally  good  surface  drainage, 
the  greater  width  requires  deeper  ditches  and  more  cost  in  con- 
struction, but  permits  a  wider  distribution  of  the  travel  when  the 
roads  are  muddy  or  rough.  The  deep  ditches  are  harder  to  main- 
tain, and  as  a  rule  the  native  soil  from  the  bottom  of  deep  ditches  is 
not  so  good  for  road  building  purposes  as  that  nearer  the  surface. 
The  cost  of  maintaining  the  road  depends  upon  the  amount  of 
traffic,  and  is  practically  independent  of  the  width.  Therefore  the 
width  to  be  improved  depends  chiefly  upon  the  width  of  the  right 
of  way,  the  character  of  the  soil,  and  the  climate.  In  a  wet  climate,, 
with  soil  easily  working  into  mud,  a  wide  wheel-way  is  desirable; 
while  in  a  dry  climate,  or  with  a  soil  not  readily  forming  mud,  a  nar- 
row wheel-way  is  preferable. 

118.  CROSS  SECTION.  The  cross  section  or  transverse  contour 
of  a  road  is  an  important  matter  with  reference  to  the  cost  of  con- 
stmction  and  of  maintenance.  The  cost  of  construction  is  chiefly 
dependent  upon  the  form  of  the  side  ditch,  and  has  already  beem 


83  EARTH    ROADS.  [CHAP.   III. 

considered  in  §  110.  The  cost  of  maintenance  depends  upon  the 
amount  of  crown  of  the  surface,  which  has  been  discussed  in  §  114. 
Figs.  9  and  10,  page  85,  show  two  forms  of  cross  section.  The 
former  has  the  smaller  side  ditch  and  a  curved  crown;  the  latter 
has  a  larger  side  ditch  and  an  upper  surface  composed  of  two  planes 
meeting  at  the  center.  Both  may  be  constructed  with  the  ordi- 
nary scraping  grader  (§  142),  and  in  both  cases  the  side  ditches 
furnish  sufficient  earth  to  make  the  crown. 

Fig.  12  shows  a  form  of  cross  section  sometimes  adopted  for 


[*  4ft  *i 

Fig.  12. — Cross  Section  of  Village  Street. 

earth  roads  m  villages  and  towns.  The  gutter  is  usually  made  next 
to  the  sidewalk,  which  is  objectionable,  since  horses  must  stand 
in  the  mud  and  water  when  hitched  in  front  of  the  property.  The 
form  shown  in  Fig.  12  is  free  from  this  objection.  A  narrow  berm 
is  left  between  the  sidewalk  and  the  edge  of  the  slope  to  prevent 
crowding  the  gutter  too  close  to  the  shade  trees,  which  are  usually 
planted  just  outside  of  the  sidewalk.  The  gutter  shown  in  Fig,  12 
decreases  the  available  wheel-way,  and  consequently  in  some  locali- 
ties would  be  undesirable.  This  cross  section  also  can  be  made  and 
maintained  with  the  ordinary  scraping  grader. 

119.  EXCAVATION  AND  EMBANKMENT.  Side  Slopes.  The 
angle  of  the  slopes  of  the  cuts  and  fills  is  designated  by  the  ratio  of 
the  horizontal  to  the  vertical  distance.  Thus,  if  the  face  of  the  fill 
has  an  inclination  of  H  feet  horizontal  to  1  foot  vertical,  the  slope  is 
designated  as  1J  to  1. 

The  slope  of  the  excavations  varies  with  the  nature  of  the  soil, 
being  for  economy  as  steep  as  its  tenacity  will  permit.  Solid  rock 
may  be  cut  with  a  slope  of  J  to  1.  Common  earth  will  stand  1  to  1, 
or  1  i  to  1 — the  latter  being  safer  and  more  usual.  Gravel  requires 
1J  to  1.  Some  clays  will  stand  1  to  1,  while  some  require  a  much 
flatter  slope — in  extreme  cases  6  to  1.  Fine  sand  requires  a  slope 
of  2  to  1,  or  3  to  1. 

The  slope  of  embankments  has  less  range  than  that  of  excava- 
tions, since  there  is  less  variety  in  the  nature  and  the  condition  of 
the  materials,  and  is  usually  1^  to  1. 


ART.   l.J 


CONSTRUCTION. 


89 


120.  In  both  railroad  and  wagon-road  work,  it  is  customary  to 
establish  all  earthwork  slopes  as  planes  intersecting  each  other  in 
right  lines.  The  original  form  is  never  maintained/  since  it  is  not  a 
form  of  equilibrium  and  stability.  Storm  water  soon  washes  away 
the  angle  formed  by  the  intersection  of  the  two  plane  surfaces  at  the 
top  of  the  embankment,  and  the  water  flowing  down  the  slope  soon 
rounds  cut  the  angle  carefully  formed  at  the  foot.  Such  construc- 
tion violates  one  of  the  fundamental  principles  of  stability,  and  it 
is  a  needless  expense  to  build  laboriously  a  form  of  construction 
which  nature  will  inevitably  destroy. 

The  transverse  contours  of  the  embankment  and  excavation 
shown  in  Figs.  13  and  14  are  designed  to  meet  the  above  objections 


!  se,    > 

\< f  i 

^ —   i 

Fig.  13. — Cross  Section  for  Embankment. 


to  the  ordinary  forms  of  construction.  These  sections  are  de- 
signed in  accordance  with  forms  of  railroad  excavations  and  em- 
bankments recommended  by  D.  J.  Whittemore,  the  distinguished 


Fig.  14. 


OT//e  OT//e 

-Cross  Section  for  Excavation. 


chief  engineer  of  the  Chicago,  Milwaukee  and  St.  Paul  Railroad, 
which  forms  have  met  with  the  unanimous  approval  of  leading  engi- 
neers.* 

It  is  customary  in  railroad -construction  to  make  the  top  of  the 
earth  embankment  wider  than  the  base  of  the  gravel  or  broken- 
stone  ballast,  which  gives  a  berm  between  the  base  of  the  ballast 
and  the  outer  edge  of  the  earth  embankment.  This  berm  has  been 
omitted  in  Figs.  12  and  13,  since  with  an  earth  surface  there  is 
nothing  corresponding  to  the  ballast. 


*  Trans.  Amer.  Soc.  of  Civil  Eng'rs,  Sept.  1894,  Vol.  33,  p.  255-66. 


SJO  EARTH    ROADS.  [CHAP.    III. 


121.  If  the  natural  slope  above  the  cut  is  long  or  steep,  a  catch- 
water  drain  should  be  constructed  along  the  upper  edge  of  the  exca- 
vation slope  to  prevent  the  surface  water  from  above  from  washing 
clown  over  the  face  of  the  cut;  but  the  catch-water  should  be  well 
back  from  the  edge  of  the  excavation,  to  prevent  the  water  in  the 
drain  from  softening  the  upper  angle  of  the  slope. 

The  slopes  of  both  excavations  and  embankments  should  be 
sowed  with  grass  seed.  Sometimes  the  material  of  the  embank- 
ment is  such  that  grass  seed  will  not  grow,  in  which  case  it  may  be 
necessary  to  lay  sod;  but  of  course  this  is  very  expensive.  The 
roots  of  the  grass  will  hold  the  earth  from  slipping,  and  prevent  the 
face  of  the  slope  from  being  gullied  out  and  washed  down. 

122.  There  is  a  tendency  for  workmen  to  leave  the  side  slopes 
of  embankments  hollow  and  those  of  excavations  rounding,  to  de- 
crease the  amount  of  labor  required.  In  inspecting  the  work,  this 
tendency  should  be  borne  in  mind. 

123.  Setting  Slope  Stakes.  For  instructions  as  to  methods  of 
staking  out  the  ground  preparatory  to  beginning  the  work  of  exca- 
vating and  embanking,  see  any  of  the  standard  volumes  on  railroad 
engineering. 

124.  Computing  Earthwork.  For  the  methods  employed"  in 
computing  the  contents  of  excavations  and  embankments,  see  any 
of  the  various  treatises  on  that  subject;  or  for  a  briefer  presentation 
of  the  subject,  see  books  on  surveying  or  railroad  engineering. 

125.  Balancing  Cuts  and  Fills.  Other  things  being  equal,  the 
most  economical  position  of  the  grade  line  is  that  which  makes  the 
amount  of  cuts  and  fills  equal  to  each  other.  If  the  cuts  are  the 
greater,  the  earth  therefrom  must  be  wasted,  i.  e.,  deposited  in  spoil 
banks;  and  if  the  fills  are  the  greater,  the  difference  must  be  ob- 
tained from  borrow  pits, — both  of  which  operations  involve  addi- 
tional expense  for  labor  and  land.  Sometimes  it  is  more  economical 
to  make  an  embankment  from  near-by  borrow  pits  than  to  bring 
the  necessary  material  from  a  far-distant  cut;  or,  vice  versa,  it  is 
sometimes  more  economical  to  waste  the  material  from  a  cut  than 
to  send  it  to  a  remote  fill.  The  most  economical  use  of  the  material 
depends  upon  the  machinery  to  be  used  in  moving  the  earth,  the 
character  of  the  earth  in  both  cuts  and  fills,  the  road  over  which  the 
earth  must  be  transported,  the  cost  of  haul,  the  price  of  land,  the 


ART.    1.]  CONSTRUCTION.  91 

liability  of  cuts  being  filled  with  snow,  etc.;  and  the  matter  must 
be  decided  by  the  engineer  to  the  best  of  his  judgment  in  each 
particular  case. 

When  the  road  lies  along  the  side  of  a  hill,  one  side  of  the  road  is 
usually  in  cut  and  the  other  in  fill;  and  it  is  customary  so  to  place 
the  center  line  that  these  two  parts  are  at  least  nearly  equal.  How- 
ever, where  the  side  slopes  are  steep,  it  is  better  to  make  the  road 
mostly  in  cuts  on  account  of  the  difficulty  of  forming  stable  fills  on 
steep,  slopes. 

126.  In  railroad  work  it  is  the  custom  to  balance  cuts  and  fills 
on  the  longitudinal  profile  of  the  road,  but  in  wagon-road  work  the 
fills  as  shown  by  the  profile  of  the  center  line  should  be  slightly  in 
excess,  to  provide  a  place  for  the  earth  taken  from  the  side  ditches. 
On  account  of  the  expense,  wagon-roads  follow  the  surface  more 
nearly  than  railroads;  and  consequently  the  earth  from  the  ditches 
is  proportionally  more  in  wagon-road  construction  than  in  railroad 
construction. 

127.  Shrinkage  of  Earthwork.  With  most  soils,  the  act  of 
excavation  so  breaks  it  up  that  it  occupies  more  space  after  excava- 
tion than  before;  but  when  the  material  has  been  placed  in  an  em- 
bankment it  will  usually  occupy  less  space  than  in  its  original  posi- 
tion. The  expansion  due  to  excavation  is  usually  8  to  12  per  cent 
of  the  volume,  and  in  extreme  cases  may  be  40  per  cent;  but  in 
placing  the  material  in  the  embankment,  it  is  compacted  by  the 
weight  of  the  embankment  itself,  by  the  pounding  of  the  hoofs,  and 
by  the  action  of  the  wheels,  until  usually  the  final  volume  is  less 
than  the  original. 

At  first  thought  it  seems  strange  that  earth  should  occupy  less 
space  when  placed  in  an  embankment  than  when  in  its  original 
position,  seeing  that  it  is  not  so  hard  and  firm,  and  that  it  will 
usually  settle  still  farther  after  the  embankment  is  completed. 
The  following  facts  account  for  this  phenomenon :  1 .  The  continued 
action  of  frost  has  made  the  soil  in  its  natural  position  more  or  less 
porous.  2.  Earths  which  have  been  lying  in  situ  for  centuries  be- 
come more  or  less  porous  through  the  slow  solution  of  their  soluble 
constituents  by  percolating  water.  3.  The  surface  soil  is  rendered 
more  or  less  porous  by  the  penetration  of  vegetable  roots  which 
subsequently  decay.     4.  There  is  ordinarily  more  or  less  soil  lost 


92  EARTH    ROADS.  [CHAP.    III. 

or  wasted  in  transporting  it  from  the  excavation  to  the  embank- 
ment. 

The  amount  of  shrinkage  depends  chiefly  upon  the  character  of 
the  material  and  the  means  by  which  it  is  put  into  the  embankment, 
and  somewhat  upon  the  moisture  of  the  soil,  the  rainfall  conditions 
while  the  work  is  in  progress  and  soon  afterwards,  and  the  depth  to 
which  frost  usually  penetrates.  If  the  soil  is  moist  when  placed  in 
the  bank,  it  will  become  more  compact  than  if  it  were  dry.  Rain 
greatly  affects  the  shrinkage,  and  embankments  put  up  during  a 
rainy  season  will  be  more  compact  than  those  built  during  a  dry 
time.  Soil  from  above  the  usual  frost  line  is  more  porous  than  that 
not  subject  to  the  heaving  effect  of  alternating  freezing  and  thawing, 
and  consequently  shrinks  more  when  put  into  an  embankment. 

The  natural  shrinkage  of  the  ordinary  soils  is  in  the  following 
order:  (1)  sand  and  sandy  gravel  least,  (2)  clay  and  clayey  soil 
intermediate,  and  (3)  loams  most.  The  shrinkage  according  to 
the  method  of  handling  is  in  the  following  order,  beginning  with 
the  least:  (1)  drag  scrapers,  (2)  wheel  scrapers,  (3)  wagons,  (4)  cars, 
(5)  wheelbarrows.  The  usual  allowance  for  shrinkage  for  drag- 
scraper  work  is  as  follows :  gravel  8  per  cent,  gravel  and  sand  9 
per  cent,  clay  and  clayey  earth  10  per  cent,  loam  and  light  sandy 
earth  12  per  cent,  loose  vegetable  surface-soil  15  per  cent.  The 
above  results  are  for  ordinary  earth,  and  do  not  apply  to  such 
unusual  materials  as  u  buckshot,"  gumbo,  very  fibrous  soil,  etc., 
which  have  a  much  greater  shrinkage.  Solid  rock  will  expand  40 
to  50  per  cent. 

The  shrinkage  of  earth  should  be  considered  in  locating  the  grade 
lines  to  balance  the  cuts  and  fills. 

128.  Settlement  of  Embankments.  The  shrinkage  of  earth- 
work referred  to  above  takes  place  chiefly  during  construction,  but 
the  continued  action  of  the  weight  of  the  embankment  and  the 
effect  of  rain  and  traffic  will  usually  cause  a  comparatively  small 
settlement  after  completion.  Sand  or  gravel  embankments  built 
with  wheel  scrapers  will  usually  settle  1  to  2  per  cent  after  comple- 
tion, and  clay  or  loam  embankments  about  2  to  3  per  cent.  With 
drag  scrapers  the  settlement  will  usually  be  a  little  less  than  the 
above ;  and  with  dump  carts  or  wagons,  a  little  more.  With  wheel- 
barrows the  settlement  is  usually  about  10  per  cent,  but  may  be  as 
much  as  25  per  cent,  depending  upon  the  moisture  in  the  soil,  the 


ART.    1.]  CONSTRUCTION.  93 

rain  during  construction,  and  the  length  of  time  under  construc- 
tion. 

The  settlement  of  the  embankment  after  completion  should  be 
taken  into  account  when  determining  whether  the  bank  has  been 
raised  to  the  proper  height.  The  embankment  should  be  built  to 
such  a  height  that  after  it  has  ceased  to  settle  it  will  be  at  grade. 
The  length  of  time  required  for  this  settlement  depends  upon  the 
weather  conditions.  The  proper  adjustment  of  the  height  of  the 
embankments  to  compensate  for  future  settlement  is  an  important 
matter  with  broken-stone  roads  and  with  pavements. 

129.  The  above  remarks  about  settlement  do  not  apply  to  em- 
bankments built  with  the  elevating  grader  (§  149).  The  settle- 
ment of  earth  roads  put  up  by  these  machines  is  of  no  importance, 
and  depends  upon  the  amount  of  rolling  they  receive. 

130.  Rolling  the  Embankment.  Many  writers  on  roads  rec- 
ommend the  rolling  of  all  new  earth  embankments.  In  view  of 
the  usual  settlement  of  banks  built  with  drag  or  wheel  scrapers,  it 
does  not  appear  that  rolling  with  a  farm  roller  would  be  very  effect- 
ive, and  a  heavier  roller  is  seldom  available.  Simply  rolling  the 
top  of  the  finished  bank  is  not  worth  much,  since  the  effect  of  the 
roller  does  not  reach  very  deep;  and,  besides,  no  roller  will  compact 
loose  earth  so  that  wheels  and  hoofs  will  not  make  depressions  in 
it.*  Further,  it  is  not  practicable  to  roll  the  bank  during  the 
progress  of  construction,  except  when  the  scraping  and  elevating 
graders  are  used.  Finally,  those  who  travel  the  road  most  are  gen- 
erally the  ones  who  pay  for  the  construction,  and  almost  univer- 
sally they  prefer  to  compact  the  earth  by  traffic. 

It  is  customary  to  roll  the  foundation  of  pavements,  but  the 
chief  object  of  so  doing  is  to  discover  soft  places  rather  than  to  con- 
solidate the  surface;  and,  besides,  the  foundation  of  a  pavement  is 
protected  from  rain  and  the  action  of  wheels,  and  therefore  the 
effect  of  the  rolling  is  permanent,  while  with  an  earth  road  it  is  not. 

131.  Over-haul.  When  earthwork  is  done  by  contract,  the  bid 
includes  the  cost  of  removing  excavated  material  and  depositing 
it  in  embankments,  provided  the  necessary  length  of  haul  does  not 
exceed  a  specified  limit.     When  the  material  must  be  carried  be- 

*  The  heaviest  steam  rollers  give  a  pressure  of  about  600  pounds  per  linear  inch, 
vvhile  wagons  frequently  give  twice  as  much  and  occasionally  three  times. 


y4  EARTH  ROADS.  [CHAP.  III. 

yond  this  limit  the  extra  distance  is  paid  for  at  a  stipulated  price  per 
cubic  yard  per  100  feet  of  haul.  This  extra  distance  is  known  by 
the  name  of  " over-haul"  or  simply  "haul."  For  an  explanation 
of  the  method  of  computing  "haul,"  see  treatises  on  earthwork  or 
books  on  railroad  surveying. 

The  specified  limit,  i.  e.,  the  distance  of  free  haul,  depends  upon 
the  conditions.  It  is  sometimes  made  as  low  as  100  feet,  and  is 
sometimes  2,000  feet — the  latter  usually  only  in  street  work.  In 
railroad  work  500  feet  is  a  common  limit. 

132.  Frequently  all  allowances  for  over-haul  are  disregarded. 
The  profiles,  estimates  of  quantities,  and  the  required  disposal  of 
material  are  shown  to  bidding  contractors;  and  they  must  then 
make  their  own  allowances,  and  bid  accordingly.  This  method  has 
the  advantage  of  avoiding  possible  disputes  as  to  the  amount  of  the 
over-haul  allowance,  and  is  adopted  by  some  railroads  on  this 
account. 

133.  Stability  of  Embankments,  The  principles  to  be  observed 
in  the  formation  of  an  embankment  depends  somewhat  upon  the 
machinery  employed  in  doing  the  work,  but  a  few  general  considera- 
tions are  not  out  of  place  here. 

Specifications  usually  require  that  "all  matter  of  vegetable 
nature  must  be  carefully  excluded  from  the  embankment."  It  is 
impracticable  to  do  this  when  the  road  passes  through  grass  land — 
particularly  if  the  grade  is  built  with  a  "road  machine"  or  "road 
grader  "  (§  142).  It  is  desirable  to  remove  brush,  tall  grass,  and  high 
weeds  from  the  space  to  be  occupied  by  the  embankment  and  the 
borrow  pit;  but  small  twigs,  leaves,  and  sod  are  no  material  detri- 
ment, and  their  removal  is  a  needless  expense — except  at  the  point 
where  the  road  passes  from  cut  to  fill.  It  is  essential  that  all  vege- 
table matter  and  loose  porous  soil  should  be  removed  at  this  point, 
otherwise  there  will  be  a  soft  place  ready  to  soak  up  water  which 
will  make  a  mud  hole  and  also  weaken  the  bank  just  below  it. 
When  an  embankment  is  to  be  made  across  a  swamp,  bog,  or  marsh, 
the  site  should  first  be  drained  as  thoroughly  as  possible.  After 
this  is  done,  if  any  considerable  amount  of  soft  oozy  matter  remains, 
it  should  if  possible  be  removed,  and  the  embankment  started  on 
the  hard  bottom.  If  the  soft  matter  is  deep,  it  may  be  necessary 
to  lay  a  foundation  of  logs  or  fascines  to  support  the  earthwork. 


AKT.  1.]  CONSTRUCTION.  95 

Perfect  solidity  should  be  the  leading  object  aimed  at,  and  all 
necessary  precautions  should  be  taken  to  prevent  or  lessen  the 
tendency  of  the  bank  to  slip.  To  secure  stability,  embankments 
should.be  built  in  successive  layers  not  more  than  three  or  four  feet 
thick,  and  the  vehicles  conveying  the  materials  should  be  required 
to  pass  over  the  bank,  so  as  to  consolidate  the  earth.  Specifica- 
tions sometimes  state  that  the  layers  shall  be  made  concave  up- 
wards, but  this  refinement  is  scarcely  ever  necessary  >  although  it  is 
well  to  see  that  the  layers  are  never  very  much  convex  upward. 
Embankments  are  sometimes  first  built  up  in  the  center,  and  after- 
wards widened  by  tipping  or  dumping  earth  over  the  side ;  but  this 
should  never  be  allowed. 

When  embankments  are  to  be  formed  on  sloping  ground,  it  may 
be  necessaiy  to  plow  the  ground  or  to  cut  steps  in  the  rocky  surface 
to  hold  the  filling  from  sliding  down  the  natural  surface.  In  many 
cases  where  roads  are  to  be  constructed  along  steep  slopes,  it  is 
found  cheaper  to  use  retaining  walls  (§  181)  to  sustain  the  road 
upon  the  lower  side  and  the  earth-cutting  on  the  upper  side  than  to 
cut  long  slopes  or  form  high  embankments. 

134.  IMPROVING  OLD  ROADS.  Country  roads  may  be  improved 
in  any  of  several  ways: 

1.  By  changing  the  location,  to  secure  better  alignment  or  lower 
gradients.  The  method  of  doing  this  has  been  discussed  in  Art.  2, 
Chapter  I. 

2.  By  cutting  down  the  hills  and  filling  up  the  hollows,  to  secure 
easier  gradients.  A  hill  may  be  cut  down  without  seriously  inter- 
fering with  traffic  by  cutting  one  side  of  the  roadway  down  a  foot 
or  two  with  drag  or  wheel  scrapers  (§  141),  and  then  turning  traffic 
on  this  portion  and  lowering  the  other  side,  continuing  to  cut  down, 
each  side  alternately  until  the  desired  depth  is  reached.  If  the 
earth  is  deposited  upon  the  embankment  in  the  hollow,  the  traffic 
will  consolidate  the  road  as  it  is  built  up,  which  is  very  desirable. 

3.  By  laying  tile  and  cutting  open  ditches,  to  improve  the  drain- 
age, as  has  been  discussed  in  §  98-113. 

4.  By  re-forming  the  surface  by  the  use  of  the  scraping  grader, 
to  improve  surface  drainage,  as  discussed  in  §  145-46. 

5.  By  adding  sand  or  gravel  to  a  clay  road,  or  clay  to  a  sand 
road,  to  improve  the  surface.     When  dry,  clay  makes  a  very  hard 


■96  EARTH    ROADS.  [CHAP.   III. 

and  durable  surface ;  but  it  absorbs  water  quite  freely  from  above, 
and  is  so  impermeable  that  it  is  not  easily  drained  from  below,  con- 
sequently clay  roads  are  very  bad  during  a  wet  time.  Clean  coarse 
sand  or  small  gravel  mixed  with  the  clay  will  form  a  hard  surface 
that  is  nearly  impervious  to  water,  and  consequently  is  not  readily 
softened  by  it.  Sand  may  be  laid  on  in  thin  layers  and  left  to  be 
worked  in  by  traffic ;  or  it  may  be  worked  in  with  a  harrow  or  culti- 
vator and  then  rolled.  Cinders  may  be  used  in  a  similar  manner; 
but  pebbles,  the  largest  of  which  are  about  the  size  of  a  pea,  are  best 
for  this  purpose.  They  should  be  laid  on  in  a  two-inch  layer  and 
then  rolled,  the  roadway  being  previously  sprinkled  if  it  is  not 
already  soft.  After  applying  and  rolling  in  a  layer  of  pebbles,  the 
road  should  be  opened  to  traffic  for  a  month  or  two,  after  which 
another  layer  should  be  added.  Three  or  four  layers  will  make  a 
road  fairly  good  except  during  a  long-continued  wet  time.  Each 
layer  will  improve  the  surface,  but  this  method  of  hardening  the 
surface  should  not  be  confounded  with  the  method  of  constructing 
gravel  roads  discussed  in  Chapter  III. 

135.  ROAD-BUILDING  MACHINERY.  In  recent  years  there  has 
been  a  great  advance  in  the  machinery  employed  in  building  earth- 
roads.  The  wheelbarrow  was  formerly  much  used  for  short  hauls,  but 
has  been  superseded  by  some  form  of  drag  scraper  (§  137)  drawn  by 
horses,  and  is  never  used  now  except  for  very  small  jobs,  or  in  wet 
and  swampy  places.  Formerly  an  embankment  was  constructed 
with  plows  and  drag  scrapers  (Fig.  15,  page  97),  while  now  it  is 
built  much  more  cheaply  and  better  with  either  the  "road  machine," 
"road  grader,"  scraping  grader  (Fig.  24,  page  102),  or  with  the  ele- 
vating gmder  (Fig.  35,  page  110).  Years  ago  earth  was  thrown  into 
wagons  or  carts  by  hand  and  hauled  to  its  destination,  while  now 
it  is  moved  with  wheel  scrapers  (Fig.  21,  page  101).  Earth  was 
formerly  moved  considerable  distances  with  the  drag  scraper,  while 
now  the  wheel  scraper  is  employed.  Formerly  the  surface  of  the 
excavation  was  finished  with  the  drag  scoop-scraper,  while  now  it  is 
done  much  better  and  more  cheaply  with  the  tongue  scraper  (Fig.  18, 
page  98)  or  the  scraping  grader. 

There  are  a  variety  of  plows,  dump  carts,  wagons,  etc.,  used  in 
moving  earth,  which  need  not  be  considered  here.  The  dump  cart 
is  much  in  favor  in  the  New  England  States,  but  is  never  used  in  the 


ART.  L] 


CONSTRUCTION. 


97 


Mississippi  Valley.  The  steam  shovel  and  dump  cars  afford  the 
most  economical  method  of  handling  earth  when  the  amount  to  be 
moved  justifies  the  outlay  for  the  plant;  but  as  that  would  seldom 
be  the  case  in  highway  work;  this  method  will  not  be  considered. 

136.  Scrapers.  Scrapers  are  generally  used  to  move  material' 
after  it  has  been  loosened  by  plowing.  There  are  two  principal 
kinds — the  drag  and  the  wheel  scraper. 

137.  Drag  Scrapers.  There  are  three  forms  of  the  drag  scrapei 
— the  scoop  (Fig.  15),  the  flat-botlomed  pole-scraper  (Fig.  18,  page 
98),  and  the  Fresno  scraper  (Fig.  19,  page  99). 

138.  The  scoop  scraper,  Fig.  15,  is  made  in  three  sizes.    The 


Fig.  15. — Drag  Scoop  Scraper. 


Fig.  16. — Scraper  with  Runners. 


Fig.  17. — Scraper  with  Double  Bottom. 


smallest,  for  one  horse,  has  a  capacity  of  3  cubic  feet;  and  the  two 
larger  sizes,  for  two  horses,  have  a  capacity  of  5  and  7  feet  respect- 
ively. Some  have  metal  runners  on  the  bottom,  Fig.  16,  and 
others  have  practically  a  double  bottom,  Fig.  17,  which  decreases 
draft  and  increases  durability.  The  best  forms  without  runners 
cost  about  $6.00,  $6.50,  and  $7.00  for  the  different  sizes  respect- 
ively. Runners  do  not  add  more  than  50  cents  to  the  above 
prices,  and  the  double  bottom,  not  more  than  $1.00. 

The  scoop  scraper  is  much  used  for  moving  earth  short  distances; 
but  with  it  there  is  difficulty  in  building  a  bank  of  uniform  solidity, 
since  each  scraperful  is  deposited  in  a  compact  mass  by  itself,  with 
low  loose  places  between  them.  Nor  is  the  scoop  scraper  suitable 
for  finishing  an  embankment,  since  the  surface  made  with  it  is  a 
succession  of  humps  and  hollows  which  is  very  trying  to  drive  over 


98  EARTH  ROADS.  [CHAP.  III. 


when  dry,  and  when  it  rains  the  low  places  fill  with  water  which 
speedily  softens  the  remainder  of  the  road,  and  finally  produces 
mud  holes.  The  tongue  scraper  (§  139)  is  much  preferable  for 
finishing  the  surface. 

The  scoop  scraper  is  sometimes  employed  in  loading  wagons. 
This  is  done  by  building  an  elevated  platform  under  which  the 
wagons  are  driven,  and  to  the  top  of  which  the  earth  is  drawn  in  a 
scoop  scraper  upon  an  inclined  runway.  In  the  middle  of  the  plat- 
form is  a  hole  through  which  the  scraper  is  dumped.  To  decrease 
the  height  of  the  platform,  the  trackway  under  the  platform  is 
excavated.  This  arrangement  of  platform  and  runways  is  called  a 
trap. 

139.  The  pole  or  tongue  scraper,  Fig.  18,  is  ordinarily  used  for 
leveling  up  the  road  surface  in  excavations,  and  is  frequently 
employed  in  preparing  the  subgrade  for  pavements.     It  may  be 


Fig.  18. — Tongue  Scraper. 

used  to  transport  earth  short  distances,  but  is  not  so  good  for  this 
purpose  as  the  scoop  scraper.  It  is  made  in  two  sizes,  36  and  48 
inches  wide,  which  cost  about  $6.00  and  $7.00  respectively,  f.  o.  b. 
factory. 

140.  The  Fresno  scraper,  Figs.  19  and  20,  is  the  outgrowth  of 
experience  in  irrigation,  and  has  some  advantages  over  the  com- 
mon scoop  scraper.  (1)  The  proportions  of  the  buck  scraper  are 
such  that  it  is  more  readily  loaded  to  its  full  capacity.  (2)  It  dis- 
tributes the  earth  on  the  bank  better,  as  it  can  be  adjusted  to  deliver 
in  layers  from  1  to  12  inches  thick.  (3)  The  runners  make  it  more 
durable.  (4)  It  is  more  easily  loaded.  (5)  It  will  follow  up  a 
steep  bank  without  dumping,  and  hence  runways  are  not  required. 


ART.    1.] 


CONSTRUCTION. 


99 


Fresno  scrapers  are  made  in  three  sizes,  the  cutting  edge  being 
3^  feet,  4  feet,  and  5  feet;  and  their  respective  capacity  is  8, 10,  and 
12  cubic  feet. 


Fig.  20. — Buck  Scraper,  Dumped 


Under  favorable  conditions  this  form  of  scraper  will  push  con- 
siderable earth  along  in  front  of  it,  and  consequently  the  capacity 


100  EARTH    ROADS.  [CHAP.    III. 

is  frequently  stated  as  much  greater  than  that  given  above.  The 
cost  is  usually  about  $17,  $18,  and  $19  respectively. 

141.  Wheel  Scrapers.  The  wheel  scraper  consists  of  a  steel 
box  mounted  on  wheels  and  furnished  with  levers  for  raising,  lower- 
ing, and  dumping.  All  of  the  movements  may  be  made  without 
stopping  the  team.  The  wheel  scraper  is  made  in  three  sizes, 
No.  1,  2,  and  3,  having  a  capacity  of  9,  12,  and  16  cubic  feet  respect- 
ively. Some  manufacturers  make  an  automatic  front  end-gate 
which  adds  materially  to  the  load  the  scraper  will  carry,  particu- 
larly on  a  rough  down-hill  road. 

Fig.  21,  22,  and  23,  page  101,  show  the  three  positions  of  the 
scraper.  The  forms  shown  have  square-end  boxes,  but  some 
manufacturers  make  a  pressed  round-end  scoop.  Some  varieties 
have  dirt-proof  hubs,  and  there  are  also  a  variety  of  styles  of  wheels. 

The  cost  of  the  three  sizes  at  the  factory  is  about  $25,  $30,  and 
$40  respectively,  varying  somewhat  with  the  details  of  construction. 

142*  Scraping  Grader.,  The  machine  shown  in  Fig.  24  and  25, 
page  102,  is  indifferently  called  a  road  machine  or  road  grader,  but 
it  will  here  be  called  the  scraping  grader  to  distinguish  it  from  the 
elevating  grader  (§  149)  and  from  other  road  machines.-  The 
scraping  grader  is  a  very  important  factor  in  caring  for  earth  roads; 
and  as  an  instrument  of  maintenance  has  been  called  a  road  hone, 
but  could  more  properly  be  called  a  road  plane. 

143.  There  are  several  forms  of  scraping  graders  of  the  type 
shown  in  Fig.  24  and  25,  which  differ  in  minor  details  but  all  of 
which  accomplish  substantially  the  same  work.  Each  consists  of 
a  frame  carried  on  four  wheels,  supporting  an  adjustable  scraper- 
blade,  the  front  end  of  which  plows  a  furrow  while  the  rear  end 
pushes  the  earth  toward  the  center  of  the  road  or  distributes  it 
uniformly  to  form  a  smooth  surface.  The  blade  can  be  set  at  any 
angle  with  the  direction  of  draft,  or  at  any  height;  and  it  may  also 
be  tilted  forward  or  backward.  This  machine  will  work  in  almost 
any  soil — even  where  a  plow  will  not.  It  is  hauled  by  horses,  and 
makes  successive  rounds  or  cuts  until  the  desired  depth  of  ditch 
and  crown  of  road  is  obtained. 

Fig.  26  to  33,  pages  104  to  108,  show  the  various  kinds  of  work 
that  may  be  done  with  this  type  of  machine. 

Note  in  Fig.  28,  page  105,  that  the- front  and  rear  wheels  do  not 


ART.   1.] 


CONSTRUCTION-. 


101 


^^ 


Fig.  21. — Wheel  Scraper,  Filling. 


Fig.  23. — Wheel  Scraper.  Dumping. 


102 


EARTH    ROADS. 


[CHAP. 


III. 


track.  The  whole  rear  end  of  the  machine  may  be  thrown  to  one 
side  or  the  other  by  operating  a  hand-wheel.  The  object  of  this 
adjustment  is  to  neutralize  the  lateral  resistance  of  the  earth  to 
being  pushed  sidewise  by  the  blade.      In  some  forms  of  the  scraping 


Fig.  24. — Austin  Scraping  Grader. 


Fig.  25. — Champion  Scraping  Grader. 

grader,  substantially  the  same  object  is  accomplished  by  shifting 
the  rear  axle  lengthwise  so  that  one  rear  wheel  bears  against  the 
unplowed  bank  of  the  ditch  (see  Fig.  33,  page  108) ;  and  in  other 
forms  the  rear  axle  is  telescoping,  and  either  rear  wheel  can  be 
moved  in  or  out  independently.  Fig.. 34,  page  109,  shows  another 
method  of  neutralizing  the  lateral  resistance  of  the  earth.  Either 
the  front  wheels  or  the  rear  one  may  be  set  at  any  inclination  by 
operating  a  hand-wheel.     The  inclined  wheel  not  only  gives  a  com- 


ART.   1.]  CONSTRUCTION.  103 


ponent  to  resist  the  lateral  thrust  of  the  earth,  but  also  prevents 
the  binding  or  cramping  of  the  hub  on  the  axle  which  occurs  in  ma- 
chines having  vertical  wheels.  The  machine  with  inclined  wheels 
has  very  recently  been  placed  upon  the  market. 

The  preceding  forms  of  scraping  grader  cost  $225  to  $250  at 
the  factory.  This  machine  is  of  inestimable  value  in  constructing 
and  maintaining  earth  roads,  as  it  does  the  work  better  and  much 
cheaper  than  it  can  be  done  either  by  hand  or  with  plows  and 
scrapers.  The  work  done  with  the  scraping  grader  is  also  superior 
to  that  done  with  plows  and  drag  scrapers,  since  the  plow  cuts 
deeper  in  some  places  than  others  and  these  places  are  left  full  of 
loose  earth  and  soon  form  holes  which  catch  and  hold  water. 

144.  In  addition  to  the  type  of  grader  shown  in  Fig.  24,  25,  and 
34,  pages  102  and  109,  there  is  on  the  market  a  cheaper  and  lighter 
machine  which  differs  from  the  forms  shown  chiefly  in  having 
wooden  wheels  and  frame,  and  less  elaborate  adjusting  devices. 

All  of  the  forms  referred  to  above  have  four  wheels,  but  there 
are  also  upon  the  market  several  varieties  consisting  of  a  blade 
carried  by  only  two  wheels.  As  this  form  of  machine  is  more  suit- 
able for  use  in  maintenance  than  in  construction,  its  consideration 
will  be  deferred  to  Art.  2,  Maintenance  (see  §  200). 

Still  another  form  of  scraping  grader  is  shown  in  Fig.  62,  page  219. 
It  is  primarily  a  land-leveling  machine.  It  differs  essentially  from 
scraping  graders  in  having  a  digging  or  plowing  apparatus  in  front 
of  the  scraping  blade,  and  in  having  adjustable  aprons  at  each  end 
of  the  blade  that  may  be  employed  to  prevent  the  earth  from  sliding 
off  at  the  end  of  the  blade.  The  scraping  blade  is  adjustable  in 
both  the  vertical  and  the  horizontal  plane.  The  price  is  $125  f .  o.  b. 
factory. 

145.  Operating  the  Scraping  Grader.  To  build  a  road  with  the 
scraping  grader,  first  plow  a  light  furrow  with  the  point  of  the  blade, 
where  the  outside  of  the  ditch  is  to  be  (see  Fig.  26,  page  104).  To 
make  the  blade  penetrate  hard  or  stony  ground,  elevate  the  rear  end 
considerably  and  use  only  the  point.  On  the  second  round,  with 
the  front  and  rear  wheels  in  line  (see  Fig.  27),  drive  the  team  so 
that  the  point  of  the  blade  will  follow  the  furrow  made  the  first 
round,  plowing  a  full  furrow  with  the  advance  end  of  the  blade,  and 
dropping  the  rear  end  somewhat  lower  than  before.     The  third  time 


104 


EARTH    ROADS. 


[chap.  III. 


Fig.  26.— Scraping  Grader  Making  First  Round. 


Fig.  27. — Scraping  Grader  Making  Second  Round. 


ART.    1.]  CONSTRUCTION.  105 


round,  move  over  toward  the  middle  of  the  road  the  earth  pre- 
viously plowed.  In  moving  the  earth  toward  the  center  of  the  road, 
elevate  the  rear  end  of  the  blade  to  allow  the  earth  to  distribute 
under  it,  so  as  to  build  the  road  at  the  side  of  the  proper  crown 
before  filling  the  center  (see  Fig.  28) ;  and  if  the  machine  slides  side- 


Fig.  28. — Scraping  Grader  Making  Third  Round. 

wise  instead  of  pushing  the  ridge  of  earth  toward  the  center,  either 
slue  the  whole  rear  end  of  the  machine  toward  the  center,  or  move 
one  hind  wheel  or  the  whole  rear  axle  laterally  until  the  rear  wheel 
bears  against  the  bottom  of  the  unplowed  bank  at  the  ditch — ac- 
cording to  the  construction  of  the  machine  (see  Fig.  28  and  33, 
page  108).  If  the  newest  form  of  scraping  grader  (Fig.  34,  page  109) 
is  employed,  there  will  be  no  tendency  to  slip.  Finally,  return  to 
the  ditch  and  plow  it  out  deeper,  moving  the  earth  over  toward  the 
middle  whenever  as  much  is  plowed  as  the  machine  can  move  at 
once.  Repeat  this  until  the  ditches  are  of  the  proper  depth,  and 
the  road  as  full  and  round  as  required. 

A  ridge  should  not  be  left  in  the  middle  of  the  road.  Usually  a 
skilful  handling  of  the  machine  will  prevent  the  formation  of  such 
a  ridge  by  elevating  the  rear  end  of  the  scraping  blade,  thus  allowing 
the  earth  to  loose  out  under  it  as  the  center  of  the  road  is  approached. 
If  the  road  is  very  rough,  it  may  not  be  possible  to  fill  all  the  ruts 
without  forming  a  ridge  in  the  center  of  the  road  at  some  places. 


106 


EARTH    ROADS. 


[chap.  hi. 


Fig.  30.— Scraping  Grader  Cutting  away  Old  Bank. 


ART.    1.] 


CONSTRUCTION. 


107 


If  the  ridge  is  formed,  it  can  be  flatted  down  by  setting  the  blade 
square  across  the  road  and  allowing  the  earth  to  flow  under  it;  and 


Fig.  31. — Scraping  Grader  Cutting  Shoulder  from  Deep  Ditch. 

with  most  machines  the  center  ridge  can  be  leveled  down  by  re- 
versing the  blade  and  using  the  back  of  it. 


Fig.  32. — Scraping  Grader  Filling  Tile  Ditch. 

If  the  ground  where  a  road  is  to  be  constructed  is  covered  with 
weeds  and  grass,  it  should  be  cleared  by  burning  or  by  mowing  anc* 


108 


EARTH  ROADS. 


[CHAP.  III. 


raking.  With  sod  ground  the  best  road  can  be  obtained  by  first 
cutting  the  sod  as  thin  as  possible  and  moving  it  to  the  center  of  the 
road,  and  then  going  back  to  the  ditch  and  continuing  the  grading 
as  described  above.  To  cut  a  thin  slice  of  sod,  the  scraper  blade 
should  be  as  sharp  as  possible.  When  the  ground  to  be  moved  is 
covered  with  sod  or  weeds,  some  operators  make  the  first  cut  on  the 


33. — Scraping  Grader  with  Adjustable  Rear  Axle. 


inside  of  the  ditch  and  at  each  successive v  round  cut  a  little  farther 
out,  thus  distributing  the  sod  through  the  earth  forming  the  road- 
way. This  requires  too  much  cutting  with  the  unsharpened  end  of 
the  blade,  and  is  therefore  not  as  good  as  the  method  described  above. 
146.  It  is  best  not  to  put  more  than  4  to  6  inches  of  loose  earth 
into  the  road  at  one  working,  as  that  is  all  that  can  be  thoroughly 
packed  by  traffic.  If  a  greater  amount  is  thrown  up  at  one  time, 
the  bottom  of  the  grade  will  remain  soft  and  cause  the  road  to  cut 
into  deep  ruts  as  soon  as  the  top  has  become  thoroughly  soaked  by 
rain.  As  far  as  possible  the  grading  should  be  done  early  in  the 
summer,  giving  ample  time  for  the  loose  earth  to  settle  and  pack 
before  the  fall  rains.  If  worked  in  the  fall,  there  should  never  be 
more  than  4  inches  of  loose  earth  put  upon  the  road  at  one  working. 


ART.   1.] 


CONSTRUCTION". 


109 


If  the  maximum  amount  of  earth  is  to  be  placed  upon  the  road 
at  once,  it  is  wise  to  roll  each  successive  layer  with  as  heavy  a  roller 
as  is  available  or  as  the  team  can  draw,  as  otherwise  traffic  will  con- 
solidate only  the  surface,  and  the  bottom  of  the  grade  will  long 
remain  soft  and  spongy. 

147.  The  scraping  grader  is  usually  drawn  by  four  or  six  horses, 
depending  upon  their  size,  and  the  character  and  condition  of  the 


Fig.  34. — Scraping  Grader  with  Inclined  Wheels. 

soil.  One  man  can  operate  the  machine,  and  one  or  two  men  are 
lequired  to  drive. 

A  traction  engine  is  sometimes  used;  and  it  is  a  better  power, 
since  it  gives  a  steady  draft  and  does  not  need  to  stop  to  rest.  At 
certain  seasons  of  the  year,  the  traction  engine  is  the  cheaper  power, 
and  at  other  times  horses  are  the  cheaper,  depending  upon  the  re- 
quirements of  horses  for  farm  work  and  the  demands  for  the  trac- 
tion engine  in  threshing  and  shelling. 

148.  The  cost  of  building  an  ordinary  prairie  road  with  this 
machine  is  about  $30  to  $40  per  mile,  with  a  width  of  30  or  35  feet 


110 


EARTH    ROADS. 


[CHAP.   III. 


and  a  crown  of  6  inches  above  the  natural  surface.  The  first  is  the 
cost  when  there  is  no  spd,and  the  second  when  there  is  a  stiff  sod.  A 
second  6  inches  may  be  added  for  about  $30  per  mile. 

If  the  ground  is  very  dry  and  hard,  another  team  and  driver  will 
be  required,  and  the  above  prices  may  be  nearly  doubled. 

149.  Elevating  Grader.  The  best  known  form  of  the  elevating 
grader  is  shown  in  Fig.  35.    It  consists  of  a  frame  resting  upon  four 


Fig.  35. — Elevating  Grader. 


wheels,  from  which  is  suspended  a  plow  and  a  frame  carrying  a 
wide  traveling  belt.  The  carrier  is  built  in  sections  and  its  height 
is  adjustable.  The  larger  carrier  will  deliver  earth  14,  17,  19,  or  22 
feet  horizontally  and  8  feet  vertically  from  the  plow;  while  the 
smaller  size  delivers  14  and  17  feet  horizontally  and  7  feet  vertically. 
The  smaller  machine  is  designed  for  highway  work.  The  plow 
loosens  the  soil  and  throws  it  upon  the  traveling  inclined  belt, 
which  delivers  it  upon  the  embankment  direct  or  into  wagons. 

This  is  an  exceedingly  effective  machine  for  building  open  ditches, 
earth  embankments,  or  filling  wagons.  By  changing  the  length  of 
the  carrier  and  by  properly  distributing  the  earth,  the  machine  will 
build  either  a  broad  low  embankment  from  a  narrow  deep  cutting, 
or  a  narrow  high  embankment  from  a  broad  shallow  cutting;  or 
the  machine  will  excavate  a  deep  narrow  ditch  with  flat  spoil  banks, 
or  a  shallow  ditch  with  narrow  spoil  banks,  This  machine  is  espe- 
cially adapted  to  building  earth  roads  in  a  prairie  country,  for 
which  purpose  it  has  been  very  largely  used. 


ART.   1.]  CONSTRUCTION.  HI 

The  large  machine  is  usually  propelled  by  twelve  horses — eight 
in  front  and  four  behind, — and  the  smaller  by  eight  in  front.  Often 
a  traction  engine  is  cheaper  than  horses.  One  man  can  operate  the 
machine;  and  at  least  two  men,  and  usually  three,  are  required  to 
drive  the  larger  machine,  but  usually  two  drive  the  smaller  one. 

150.  The  factory  price  of  the  smaller  machine  is  $1,200. 

The  large  machine  is  guaranteed  to  place  1,000  cubic  yards  of 
earth  in  an  embankment  in  10  hours,  or  to  load  600  cubic  yards  into 
wagons  in  the  same  time.  The  small  machine  will  grade  a  quarter 
of  a  mile  of  ordinary  prairie  road  per  day,  with  a  width  of  25  to  30 
feet  and  a  crown  of  12  inches  at  the  center,  at  a  cost  of  $11  to  $14, 
or  at  the  rate  of,  say,  $45  to  $60  per  mile. 

151.  Recently  there  have  appeared  upon  the  market  two  forms 
of  elevating  graders  consisting  of  a  plow,  carrier,  and  traction  engine 
combined.  So  far  as  known  these  are  still  in  the  experimental 
stage. 

152.  Operating  the  Elevating  Grader.  To  build  a  new  road  of 
the  sections  shown  in  Fig.  9  and  10,  page  85,  first  mark  by  stakes 
a  line  10  feet  on  each  side  of  the  center  of  the  proposed  road. 
With  the  machine  arranged  to  carry  17  feet,  drive  along  the  left- 
hand  row  of  stakes  and  back  on  the  other  side  of  the  road  in  the 
same  way.  The  streams  of  earth  as  delivered  will  overlap  5  or  6 
feet.  Start  the  machine  on  the  second  round  with  the  right-hand 
forward  wheel  in  the  furrow  of  the  previous  round,  and  complete 
the  round.  A  harrow  should  follow  the  machine  to  break  up  the 
sod  and  level  the  bank.  Continue  to  make  rounds  until  the  ditches 
are  as  wide  as  desired. 

Commence  the  second  plowing  by  bringing  the  left-hand  wheel 
of  the  machine  to  the  left-hand  edge  of  the  first  furrow  cut,  which 
brings  the  plow  one  furrow  to  the  left  of  the  point  of  commencing 
the  first  plowing,  and  keep  this  relative  position  while  making  this 
round.  Make  the  second  round  with  the  right-hand  forward  wheel 
in  the  furrow  of  the  previous  round;  and  continue  to  make  rounds 
until  the  outside  of  the  ditch  is  reached  again.  For  the  best  results 
a  harrow  and  roller — the  heavier  the  better — should  follow  the 
grader  during  the  second  and  subsequent  rounds.  See  Fig.  36, 
page  112. 

When  the  second  plowing  has  been  completed,  the  grade  will  be 


in 


EARTH    ROADS. 


[CHAP.   III. 


high  and  narrow;  and  therefore  the  carrier  should  be  shortened  to 
14  feet.  Then  start  the  machine  so  that  the  plow  will  take  a  furrow 
from  the  center  of  the  ditch,  and  continue  the  third  plowing,  as 
described  above  for  the  first  and  second,  to  the  outside  of  the  ditch. 
For  the  fourth  plowing  take  a  couple  of  furrows  from  the  outside  of 
the  excavation  to  deepen  the  ditch. 

The  final  result  should  be  about  as  in  Fig.  9,  page  85.  Most 
operators,  however,  leave  a  berm  at  the  inside  edge  of  the  ditch 
(see  Fig.  36),  which  is  undesirable  since  it  interferes  with  the  opera- 
tion of  the  scraping  grader  in  maintaining  the  road. 


Fig.  36. — Elevating  Grader  Building  Earth  Road. 

153.  For  loading  wagons,  the  carrier  is  arranged  to  deliver  at  17 
or  19  feet  horizontally  from  the  machine,  the  wagons  are  driven  so 
that  the  earth  falls  from  the  carrier  into  the  wagon,  and  both  move 
at  the  same  speed  until  the  wagon  is  loaded;  and  then  the  grader 
slows  down  while  the  loaded  wagon  drives  out  and  an  empty  one 
drives  in.  In  a  public  test  at  Denver,  Colorado,  in  189.0,.  55  dump 
wagons  were  loaded  in  22  minutes,  or  at  the  rate  of  150  wagons  per 
hour.*  Common  wagons  with  dump  boards  are  not  so  easily  loaded 
as  the  usual  dump  wagon,  since  they  are  narrower  and  longer.     It 


*  Manufacturer's  catalogue. 


AKT.    1.]  CONSTRUCTION.  113 

is  customary  to  estimate  three  dump  wagons  for  the  first  100  feet 
of  haul,  and  an  additional  wagon  for  each  100  feet  thereafter. 

154.  COST  OF  EARTHWORK.  Of  necessity,  general  estimates  of 
the  cost  of  earthwork  can  not  be  very  exact,  since  the  cost  will  vary 
with  the  condition  of  the  soil,  the  wages,  the  hours  constituting  a 
day's  work,  the  relative  amount  paid  for  supervision,  the  effective- 
ness of  the  supervision,  the  facilities  for  preventing  one  part  of  the 
crew  from  interfering  with  the  work  of  another,  the  proper  adjust- 
ment of  the  number  of  shovelers  per  cart  *  or  of  scraper  holders  to 
scrapers,  etc.  The  following  data  have  been  checked  by  engineers 
and  contractors  of  wide  experience  and  are  believed  to  be  reason- 
ably reliable. 

155.  In  the  analysis  of  the  cost  of  earthwork  to  follow,  the  price 
for  a  man  will  be  assumed  to  be  $1.50  per  day  of  10  hours,  and  that 
for  a  team  and  driver  $3.50  per  day.  These  are  the  usual  wages 
paid  by  contractors,  which  are  the  prices  to  be  considered  here;  for 
if  the  work  is  done  under  the  labor-tax  system  ordinary  estimates 
will  not  apply  (see  §  52-53),  and  if  the  farmer  hires  out  to  do  the 
work  of  a  teamster  he  usually  demands  the  ordinary  pay  for  that 
class  of  work.  These  are  about  the  prices  that  have  been  estab- 
lished for  a  number  of  years  in  a  number  of  states.  Of  course 
wages  may  be  a  little  more  when  work  is  being  rushed,  or  a  little 
less  when  work  is  scarce. 

156.  Cost  with  Scraping  Grader.  In  prairie  soil,  two  men  and 
four  horses  with  a  scraping  grader  can  build  a  mile  of  road  36  feet 
wide  from  inside  to  inside  of  ditch  with  a  crown  of  6  inches  at  the 
center  after  being  compacted,  for  $30  to  $40,  which  is  equivalent  to 
If  or  2\  cents  per  cubic  yard.  The  first  is  the  cost  when  there  is 
no  sod,  and  the  last  when  there  is  sod.  The  cost  for  a  crown  of  12 
inches  will  be  about  $70  per  mile,  or  1}  cents  per  cubic  yard.  The 
above  prices  do  not  include  interest,  or  wear  and  tear  of  grader, 
which  would  be  about  \  cent  per  cubic  yard.     The  total  cost  for 


*  For  an  interesting  and  instructive  example  of  the  way  in  which,  by  organiza- 
tion and  management,  the  amount  of  earth  shoveled  into  a  cart  was  nearly  double 
that  ordinarily  considered  a  fair  average,  and  the  total  cost  of  moving  the  earth 
was  only  about  half  the  usual  amount — all  without  rushing, — see  Annual  Report  of 
the  Connecticut  Civil  Engineers  and  Surveyors  for  1901,  p.  148-56;  or  a  full 
abstract  of  the  same  in  Engineering  News  for  Jan.  17,  1901,  Vol.  45,  p.  54-55. 


114  EARTH  ROADS.  [CHAP.  Ill, 

scraping-grader  work  in  prairie  soil  usually  varies  between  If  and  2£ 
cents  per  cubic  yard. 

In  hard  soil  requiring  an  extra  team  and  hence  another  driver, 
add  one  half  to  the  above  prices. 

157.  Cost  with  Elevating  Grader.  The  manufacturers  guar- 
antee that  the  elevating  grader  shown  in  Fig.  35,  page  110,  will 
deposit  1,000  cubic  yards  per  day  of  10  hours;  and  a  number  of  testi- 
monials are  printed  showing  that  1,400  to  1,600  cubic  yards  is  not 
unusual.  This  machine  is  guaranteed  to  load  into  wagons  600  yards 
per  day,  which  is  a  cost  of  about  3  cents  per  cubic  yard;  and  the 
manufacturers  claim  that  it  can  be  done  for  about  half  this  sum. 

A  contractor  in  sandy  prairie  soil  with  fourteen  horses  and  four 
men  loaded  100  cubic  yards  per  hour  as  a  maximum  and  60  as  an 
average,  the  cost  being  as  follows:  7  two-horse  teams  at  $2.50  each 
plus  2  drivers  at  $2.00  each  plus  1  operator  at  $2.00  and  1  at  $2.50 
=  $29.50,  which  for  an  average  of  600  cubic  yards  is  per  day  equiv- 
alent to  4.9  cents  per  cubic  yard.  Ordinarily  the  cost  of  depositing 
earth  direct  in  the  embankment  with  an  elevating  grader  varies 
from  6^  cents  to  8£  cents,  exclusive  of  interest,  depreciation,  and 
administration. 

158.  Cost  with  Drag-Scoop  Scraper.  Drag  scrapers  are  admi- 
rably adapted  for  borrowing  at  the  sides  of  embankments  and  for 
wasting  from  cuts  or  ditches,  and  also  for  opening  the  mouth  of 
large  cuts;  but  are  not  economical  except  for  short  distances. 
There  is  no  danger  of  the  scraper  getting  out  of  order  until  it  is  worn 
out  and  unfit  for  use,  and  the  manner  of  using  it  is  quickly  learned 
by  any  one.  Drag  scrapers  are  made  in  three  sizes  having  a  capacity 
of  3,  5,  and  7  cubic  feet,  respectively;  but  it  must  not  be  assumed 
that  each  scraper  will  carry  to  the  embankment  an  amount  equal  to 
its  rated  capacity,  since  in  the  first  place  it  is  difficult  to  completely 
fill  the  scraper,  and  in  the  second  place  the  scraper  carries  loose 
earth  which  will  shrink  about  25  per  cent  when  compacted  in  the 
embankment.  Unless  the  soil  is  very  loose  and  easily  loaded,  it  is 
not  safe  to  assume  that  each  trip  of  the  scraper  will  make  of  com- 
pleted embankment  more  than  one  half  of  its  rated  capacity.  The 
larger  size  is  most  economical,  but  the  relative  advantage  is  not 
proportional  to  the  size,  since  the  larger  size  is  not  as  easily  handled 
nor  as  easy  to  fill.      Scrapers  should  be  used  in  gangs  of  not  less 


AKT.    1.]  CONSTRUCTION.  115 

than  six  to  decrease  the  cost  of  loading,  superintendence,  spread- 
ing, etc. 

159.  Cost  of  Loosening.  Sand  or  sandy  loam  can  be  scraped 
without  plowing.  In  loam  a  two-horse  team  and  plow  will  loosen 
400  cubic  yards  per  day,  at  a  cost  of  $3.50  for  team,  plow,  and  driver, 
and  $1.50  for  the  plow  holder,  making  a  total  of  $5.00,  or  1^  cents 
per  cubic  yard.  Sometimes  the  driver  can  also  hold  the  plow,  in 
which  case  loosening  will  cost  about  1  cent  per  cubic  yard,  since  the 
team  will  not  do  quite  as  much  work  as  when  there  is  a  plow  holder 
and  also  a  driver.  If  the  ground  is  hard  it  will  be  necessary  to  add 
another  team  and  also  a  man  to  "ride"  the  beam  of  the  plow.  If 
the  ground  is  not  very  hard,  this  force  will  loosen  400  yards  per  day 
at  a  cost  of  2.1  cents  per  cubic  yard. 

160.  Cost  for  25-foot  Haul.  The  cost  of  building  an  embank- 
ment from  a  borrow  pit  at  the  side  of  the  road  will  first  be  considered. 
For  a  60-foot  right  of  way  and  a  light  embankment,  the  length  of 
haul  or  "lead"  from  center  of  gravity  of  the  fill  to  the  center  of 
gravity  of  the  cut  will  be  about  25  feet.  This  distance  will  be  a 
little  more  or  a  little  less  according  to  the  height  and  width  of  the 
bank,  and  the  width  reserved  for  sidewalk ;  but  slight  difference  in 
length  of  short  hauls  make  comparatively  little  difference  in  the 
cost  of  moving  the  earth,  because  in  the  first  place  a  considerable 
part  of  the  cost  of  hauling  is  due  to  time  consumed  in  turning  and 
loading,  and  in  the  second  place  the  cost  of  transportation  is  only 
about  half  the  total  cost  of  moving  the  earth. 

On  the  road,  an  ordinary  team  will  travel  220  feet  per  minute 
(2J  miles  per  hour),  but  in  scraping  considerable  time  is  consumed 
in  turning,  waiting  to  load,  etc.,  and  besides,  the  distance  traveled  is 
more  than  that  from  the  center  of  cut  to  the  center  of  fill;  therefore 
the  ordinary  speed  of  the  team  is  no  guide  in  this  connnection. 
Experience  shows  that  a  team  will  use  from  a  minute  to  a  minute 
and  a  half  in  making  a  round  trip  at  the  above  distance,  or,  say,  1J 
minutes  per  trip.  A  foot  vertically  is  equivalent  to  10  to  25  feet 
horizontally  (see  §  74),  and  in  estimating  the  length  of  haul  this 
fact  must  be  taken  into  account. 

The  scraperful  will  make  3^  cubic  feet  of  compacted  embank- 
ment, or  will  require  eight  trips  per  cubic  yard.  Therefore  a  team 
will  place  a  yard  of  earth  in  the  fill  every  ten  minutes,  or  6  yards 


116  EARTH  ROADS.  [CHAP.  III. 

per  hour  and  60  yards  per  day.  In  light  loose  earth,  where  it  is 
easy  fully  to  fill  the  scrapers,  a  team  may  make  70  yards;  but  if  the 
ground  is  hard,  or  obstructed  with  roots  and  grass,  50  yards  may 
be  the  maximum.  Assuming  a  day's  work  to  be  60  yards,  the  cost 
of  hauling  is  $3.50-^-60  =  5.83  cents  per  cubic  yard. 

One  man  will  hold  and  fill  the  scraper  for  two  teams  at  a  cost  of 
$1.50-^(2x60)  =  1.25  cents  per  yard.  One  man  on  the  dump  will 
ditribute  and  level  the  earth  deposited  by  six  teams,  at  a  cost  of 
$1. 50 -T- (6X60)  =  0.4  cents  per  cubic  yard.  One  foreman  will  be 
required  at,  say,  $2.50  per  day,  or  $2.50-^(6x60)  =  0.69  cents  per 
cubic  yard.  For  wear  and  tear  of  scraper  we  may  allow  10  cents 
per  day  for  each,  or  60  cents  for  the  lot;  and  for  wear  of  plow  and 
cost  of  sharpening,  say,  30  cents,  making  a  total  of  90  cents  or  0.25 
cents  per  cubic  yard.  In  very  hard  ground  the  above  prices  may 
be  doubled. 

The  total  cost  of  moving  earth  25  feet  will  then  be  as  in  Table  14, 
page  118. 

161.  Cost  for  50-foot  Haul.  We  will  next  consider  the  cost  for  a 
50-foot  haul.  At  this  distance  a  scraper  holder  can  fill  for  three 
teams.  Each  team  can  put  in  about  50  cubic  yards  per  day.  The 
other  items  will  be  substantially  as  for  a  25-foot  haul,  and  the  total 
cost  will  be  as  in  Table  14. 

162.  Cost  for  100-foot  Haul.  Each  team  will  make  a  trip  in 
about  2h  minutes,  and  will  put  in  40  cubic  yards  per  day.  The 
total  cost  will  be  as  in  Table  14. 

163.  Cost  for  200-foot  Haul.  At  this  distance  a  scraper  holder 
can  fill  for  four  teams.  Each  team  will  make  the  trip  in  about  3? 
minutes,  and  put  in  about  35  cubic  yards  per  day.  The  total  cost 
will  then  be  as  in  Table  14. 

164.  Cost  for  Hard  Ground.  If  the  ground  is  so  difficult  to  plow 
as  to  require  a  second  team  and  a  man  to  ride  the  beam,  add  1  or  1£ 
cents  to  the  values  in  Table  14  for  the  extra  cost  of  loosening;  and 
add,  say,  one  fifth  to  the  cost  of  hauling  to  allow  for  the  fact  that 
in  hard  ground  the  scrapers  are  not  as  well  filled  as  in  loose  light 
soil.  Also  add  one  half  to  the  above  estimated  cost  of  wear  and 
tear.     The  results  for  hard  ground  are  then  as  in  Table  14. 

165.  Cost  with  Wheel  Scrapers.  Wheel  scrapers  are  excellent 
for  hauling  earth  distances  up  to  600  or  700  feet.     They  are  made 


AET.   1.]  CONSTRUCTION.  11? 

in  three  sizes,  No.  1,  2,  and  3,  having  a  capacity  of  9,  12.  and  15 
cubic  feet  respectively.  With  No.  1  the  team  fills  its  own  scraper, 
while  with  No.  3  an  extra  team,  a  snatch  team,  is  required  to  fill 
the  scrapers  reasonably  full,  and  unless  the  ground  is  very  loose  and 
light  an  extra  team  is  required  to  fill  No.  2.  Most  contractors  use 
either  No.  1  with  a  single  team  or  No.  3  with  a  snatch  team.  It 
usually  takes  about  five  loads  with  No.  1  to  make  a  cubic  yard  in 
place;  four,  with  No.  2;  and  three,  with  No.  3. 

166.  Cost  for  100-foot  Haul.  It  is  assumed  that  the  scrapers 
will  be  worked  in  a  gang  of  six,  which  will  require  one  foreman,  one 
plow,  three  scraper  holders,  and  one  man  on  the  dump.  The  ex- 
pense for  these  items  will  be  the  same  as  for  the  drag  scrapers, 
and  are  so  entered  in  Table  15,  page  119.  At  this  distance  a  trip 
will  occupy  2h  minutes,  and  a  yard  will  be  deposited  every  10  min- 
utes, or  60  yards  per  day,  at  a  total  cost  of  $3.50  or  5.83  cents  per 
cubic  yard  for  hauling. 

The  wear  and  tear  is  computed  on  the  assumption  that  a  scraper 
will  last  for  200  days'  continuous  work,  making  a  cost  for  deprecia- 
tion and  repairs  of,  say,  20  cents  per  day  per  scraper.  The  wear 
and  tear  on  the  plow  will  be  estimated  at  30  cents  per  day.  The 
total  cost  will  then  be  as  in  Table  15. 

167.  Notice  that  the  cost  for  100  feet  with  the  wheel  scraper  is 
9.99  cents  per  cubic  yard,  while  with  the  drag  scraper  for  the  same 
distance  it  is  12.67  cents.  The  difference  is  in  the  cost  of  hauling, 
and  is  due  to  the  difference  in  the  capacity  of  the  two  scrapers. 

168.  Cost  for  200-foot  Haul.  A  trip  will  be  made  in  about  4 
minutes,  and  each  scraper  will  put  in  50  cubic  yards  per  day.  The 
three  scraper  holders  can  fill  an  additional  scraper,  making  nine 
in  all.     The  cost  will  then  be  as  in  Table  15. 

169.  Cost  for  300-foot  Haul.  In  this  case  another  scraper  can 
be  added,  making  four  teams  to  each  scraper  holder.  A  trip  can 
be  made  in  about  5J  minutes,  and  each  team  will  move  45  yards 
per  day.     The  cost  will  be  as  stated  in  Table  15. 

170.  Cost  for  400- foot  Haul.  It  is  difficult  to  determine  the 
most  economic  distance  for  each  size  of  scraper,  since  the  several 
sizes  are  seldom  available  for  making  the  test.  However,  at  300 
feet,  the  cost  with  a  No.  2  scraper  is  about  the  same  as  with  a 
No.  1  at  200  feet;  and  at  400  feet  the  cost  with  a  No.  2  is  about  the 


118 


EARTH    ROADS. 


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120  EARTH  ROADS.  [CHAP.  III. 

same  as  with  a  No.  1  at  300  feet.     But  at  400  feet  a  No.  3  is  more 
economical  than  a  No.  2. 

A  snatch  team  is  required  in  filling  No.  3  scrapers.  The  extra 
force  acquired  by  using  the  extra  team  completely  fills  the  scraper, 
and  also  packs  the  load  so  that  it  is  less  liable  to  spill  than  when 
loaded  by  a  single  team.  For  this  distance  it  is  most  economical 
to  work  the  scrapers  in  a  gang  of  eight;  and  two  men  will  be  re- 
quired to  hold  the  scrapers  while  being  filled.  Each  team  will  put 
into  place  45  cubic  yards,  or  360  for  the  gang.  The  total  cost  will 
be  as  shown  in  Table  15. 

171.  Cost  for  Other  Distances.  For  each  additional  100  feet  of 
lead,  add  1  cent  per  cubic  yard  to  the  cost  of  haul;  and  the  total 
cost  will  be  approximately  as  shown  in  Table  15. 

When  the  amount  of  earth  to  be  moved  is  considerable  and  the 
length  of  haul  is  great,  something  must  be  allowed  for  keeping  in 
repair  the  road  over  which  the  earth  is  transported.  A  wheel 
scraper  is  prone  to  wear  a  series  of  humps  and  hollows  along  the 
road  it  traverses,  and  these  must  be  kept  in  subjection,  if  the  work 
is  to  be  done  at  reasonable  cost.  The  proper  allowance  will  vary 
greatly  with  the  soil,  the  weather,  etc.  Trau twine  recommends 
0.1  cent  per  cubic  yard  per  100  feet  for  this  expense. 

172.  It  is  difficult  to  determine  at  what  distance  wagons  should 
supersede  wheel  scrapers;  but  usually  the  economic  limit  for  wheel 
scrapers  is  600  to  800  feet,  and  it  is  seldom  wise  to  use  scrapers 
beyond  800  feet — unless  they  are  at  hand  and  wagons  are  not. 

173.  Cost  with  Wagons.  It  will  be  assumed  that  the  wagons 
are  used  in  gangs  of  nine,  and  haul  700  to  800  feet.  If  the  roads  are 
level  and  fairly  smooth,  a  load  will  make  about  1|  cubic  yards  in 
place,  and  with  ordinary  roads  1  yard  will  make  a  load;  but  if  the 
roads  are  soft  and  steep  J  of  a  yard  may  make  a  load.  The  amount 
a  team  can  deliver  will  vary  greatly  with  the  time  consumed  in 
waiting  to  load  and  in  loading.  With  short  wagon-hauls  and  well- 
organized  work,  half  of  the  time  is  thus  consumed,  and  many  times 
much  more  is  thus  consumed.  The  time  of  the  wagon  while  loading 
should  be  considered  as  a  part  of  the  cost  of  loading,  and  this  will 
be  discussed  more  fully  in  the  next  paragraph.  For  the  above  dis- 
tance, the  round  trip  will  consume  15  minutes;  and  assuming  a 


ART.  1.]  CONSTRUCTION.  121 

yard  as  a  load,  each  wagon  will  deliver  50  cubic  yards  per  day,  at  a 
cost  of  7.00  cents  per  cubic  yard  for  hauling. 

There  is  very  great  variation  in  the  amount  of  earth  a  shoveler 
will  load  in  a  day.  In  well  managed  work,  the  shovelers  are  not 
actually  engaged  in  loading  much  more  than  half  of  the  time ;  while 
under  poor  management,  they  do  not  really  work  half  of  the  time. 
With  short  intervals  of  rest  equal  to  the  working  time,  a  man  should 
load,  in  a  day  of  10  hours,  20  cubic  yards  of  light  sandy  soil,  17 
yards  of  loam,  and  15  of  heavy  soil — provided  all  are  loosened  by 
plowing  or  picking.  Usually  five  or  seven  men  are  set  to  load  a 
wagon — two  or  three  on  each  side  and  one  at  the  rear.  Seven  men 
will  load  a  wagon  with  loam  in  5  minutes,  8  minutes  will  be  con- 
sumed in  traveling  to  and  from  the  dump,  1  minute  in  dumping, 
and  1  minute  in  getting  into  and  out  of  the  cut — making  in  all  15 
minutes  for  a  round  trip;  and  therefore  the  cost  for  wagon  and 
team  is  8.75  cents  per  cubic  yard,  as  above.  In  this  case  the  team 
works  only  about  half  the  time.  If  only  five  men  are  engaged  in 
loading  a  wagon,  7  minutes  will  be  consumed  in  loading,  and  the 
time  for  a  round  trip  will  be  17  minutes,  and  each  wagon  will  deliver 
only  35  cubic  yards,  making  the  cost  10  cents  per  cubic  yard.  In 
this  case,  the  team  really  works  less  than  half  the  time.  If  the  men 
shovel  only  12  to  15  cubic  yards  each,  as  is  very  common,  the  loss 
by  the  wagon's  waiting  for  a  load  is  considerably  more  than  the 
above.  The  proper  number  of  men  to  be  set  to  loading  a  wagon 
depends  upon  the  relative  wages  of  shoveler  and  wagon,  upon  the 
length  of  the  haul,  and  upon  the  quantity  loaded  per  day  per  man.* 
Usually  seven  shovelers  are  employed  to  each  wagon,  but  this 
number  is  not  enough  to  secure  the  greatest  economy.  In  the  fol- 
lowing estimates  it  will  be  assumed  that  nine  shovelers  are  em- 
ployed to  each  wagon.  At  the  above  distance,  nine  shovelers,  each 
loading  17  yards  per  day,  will  be  required  to  keep  three  wagons 
going,  each  of  which  deposits  45  cubic  yards  per  day.  The  cost  of 
loading  will  then  be  8.8  cents  per  cubic  yard. 

The  cost  of  leveling  the  dump  is  small,  if  dump  wagons  are  used 

*  For  the  details  of  a  very  ingenious  and  effective  adjustment  of  these  relations, 
see  an  article  by  G.  A.  Parker,  in  Proceedings  of  Connecticut  Civil  Engineers  and 
Surveyors,  1901,  p.  148-56 ;  or  a  full  abstract  of  the  same  in  Engineering  News,  Jan. 
7,  1901,  Vol.  45,  p.  54-55. 


122  EARTH  ROADS.  [CHAP.  Til. 

and  the  earth  is  dumped  over  the  end  of  the  embankment  or  wasted; 
and  it  may  be  taken  the  same  as  for  scrapers,  i.  e.,  at  0.40  cents 
per  cubic  yard.  But  dump  wagons  are  so  heavy  and  expensive 
that  they  are  seldom  used;  and  if  ordinary  wagons  with  dump 
boards  are  employed,  the  expense  for  labor  on  the  dump  will  be 
about  three  times  as  great  as  above,  or,  say,  1.20  cents  per  cubic 
yard. 

The  driver  furnishes  his  own  wagon,  and  hence  no  account  is 
taken  of  the  wear  and  tear  of  it.  There  should  be  a  small  allowance 
made  for  the  wear  and  care  of  shovels,  say,  0.1  cent  per  cubic  yard. 

The  total  cost  of  moving  earth  700  to  800  feet  with  wagons, 
then,  is  as  follows: 

1.  Loosening 1 .25  cts.  per  cu.  yd 

2.  Shoveling 8.80    "     "     "     " 

3.  Hauling  700  to  800  feet 7 .  00    "     "     "     " 

4.  Helper  on  dump 1 .20    "     "     "     " 

5.  Superintendence 0.69"      "     "     " 

6.  Depreciation  of  shovels 0. 10 

7:  Water  boy 0.16 


a       a       ti 
k       a       a 


Total  cost 18.20"     "     "     " 

174.  For  longer  distances  add  1  cent  per  cubic  yard  for  each 
100  feet  of  distance — the  usual  charge  for  over-haul. 

175.  Other  Methods.  When  the  haul  is  more  than  600  or  800 
feet,  and  when  the  amount  of  work  to  be  done  is  sufficient  to  justify 
the  initial  expense,  it  is  more  economical  to  use  portable  track  and 
small  dump  cars  than  to  use  wagons.  However,  such  conditions 
seldom  occur  in  wagon-road  construction. 

176.  Finishing  the  Slopes.  In  addition  to  the  elements  of 
cost  discussed  above,  there  is  always  some  expense  in  leveling  off 
the  bottom  of  the  cut,  in  digging  ditches,  in  trimming  up  the  slopes 
of  embankments  and  excavations,  and  in  cutting  a  catch-water  at 
the  top  of  the  slope  in  excavation.  The  cost  of  these  items  will 
vary  greatly  with  the  degree  of  finish  required  and  also  with  the 
depth  of  the  cut  or  the  fill;  and  it  may  amount  to  0.25  or  0.50  of 
a  cent  per  cubic  yard.  If  the  bottom  of  the  cut  can  be  leveled  off 
with  the  scraping  grader,  and  if  the  ditch  also  can  be  made  with 
this  machine,  the  cost  of  this  item  will  be  considerably  reduced. 


ART.   1.]  CONSTRUCTION-.  123 

177.  Profits  and  Administration.  The  proper  allowance  under 
this  head  will  vary  according  to  the  magnitude  of  the  work,  the 
risks  involved,  etc.;  but  will  usually  be  5  to  15  per  cent.  Out  of 
this  the  contractor  must  pay  the  expense  of  assembling  the  plant, 
the  cost  of  tool  house,  the  wear  and  tear  on  small  tools,  interest 
on  investment,  profits,  etc. 

178.  BRIDGES.  This  subject  will  not  be  considered  here,  since 
the  space  available  is  not  sufficient,  and  since  there  are  a  number 
of  elaborate  treatises  on  bridges.  None  of  these,  however,  gives 
an  adequate  treatment  of  the  very  small  highway  bridge  or  fairly 
represents  current  practice  for  moderate  spans. 

179.  WATERWAYS.  The  determination  of  the  amount  of 
waterway  required  for  any  particular  bridge  or  culvert  is  a  matter 
of  importance.  Although  the  problem  does  not  admit  of  an  exact 
mathematical  solution,  it  requires  intelligent  treatment.  For  a 
discussion  of  this  subject,  see  pages  391-96  of  the  author's  Masonry 
Construction.* 

180.  CULVERTS.  For  a  discussion  of  the  cost  and  method  of 
construction  of  culverts — wood  box,  vitrified  pipe,  cast-iron  pipe, 
stone  box,  and  masonry-arch  culverts, — see  the  author's  Masonry 
Construction,  pages  396-439.* 

One  common  defect  of  earth  roads  is  that  culverts  are  made  too 
short,  which  concentrates  the  traffic  upon  the  portion  of  the  road 
usually  least  able  to  bear  it.  A  short  culvert  may  be  permissible 
when  the  cost  per  unit  of  length  is  great,  but  the  defect  is  common 
where  this  cost  is  quite  small. 

181.  RETAINING  WALLS.  Retaining  walls  are  masonry  struc- 
tures employed  to  support  the  sides  of  roads  on  hill-sides  or  in  places 
where  land  for  the  ordinary  earth  slopes  is  not  readily  obtainable. 
For  a  discussion  of  retaining  walls,  see  the  author's  Masonry  Con- 
struction, pages  338-52.* 

182.  GUARD  RAILS.  Roads  on  steep  hill-sides  or  on  high  em- 
bankments, and  particularly  on  sharp  curves  in  mountain  roads, 
should  be  protected  to  insure  vehicles  against  the  possibility  of 
falling  down  the  slope.  In  Europe  such  protection  is  usually 
afforded  by  a  stone  wall,  or  by  stone  posts  set  at  frequent  intervals. 

*  A  Treatise  on  Masonry  Construction,  by  Ira  O.  Baker,  556  +  56  pp.,  6x9  inches, 
cloth,  9th  edition.     John  Wiley  &  Sons,  New  York.     Price  $5.00. 


124:  EARTH    ROADS.  [CHAP.    III. 

In  this  country  the  usual  protection  is  by  means  of  wood  posts  and 
wood  guard  rails.  On  the  state-aid  roads  in  Massachusetts,  the 
specifications  for  the  guard  rails  are  as  follows:  "  Posts  of  cedar,  or 
other  wood  which  endures  well  in  the  soil,  are  set  at  intervals  of  8 
feet,  and  1  foot  in  from  the  edge  of  the  embankment.  These  posts 
are  planted  to  the  depth  of  3  feet,  and  project  for  3  feet  6  inches 
above  the  ground.  The  top  of  this  post  is  transversely  notched,  so 
as  to  receive  one  half  of  a  rail  four  inches  square.  Half-way  down, 
the  post  is  notched  to  receive  another  rail  two  by  six  inches  in  size. 
These  rails,  preferably  of  planed  spruce  wood,  are  spiked  to  the 
posts.  To  insure  the  better  preservation  of  the  wood  and  its 
visibility  in  the  night-time,  it  is  painted  with  two  coats  of  oil  paint 
of  some  light  color."  For  a  diagram  of  this  guard  rail,  see  Fig.  54, 
page  210. 

The  Massachusetts  Highway  Commission  wherever  practicable 
•widens  the  base  of  the  embankment  until  a  slope  of  1  to  4  is  ob- 
tained, and  then  dispenses  with  the  guard  rail.  This  plan  is  be- 
lieved to  be  more  economical,  and  to  give  a  better  appearance. 

183.  GUIDE  POSTS.  Some  states,  by  statute,  require  guide 
posts  at  all  intersections,  and  their  value  to  the  occasional  traveler 
is  sufficient  to  justify  the  expense.  The  guide  post  may  be  a  plain 
post,  supporting  near  its  top  a  board  upon  which  is  the  name  of 
the  place  reached  by  the  intersecting  road,  with  figures  showing 
the  distance,  and  a  R^T'  to  show  the  direction. 

184.  ARTISTIC  TREATMENT.  Engineers  are  accustomed  to 
study  chiefly  or  only  the  economic  side  of  construction,  and  are 
therefore  likely  to  neglect  the  artistic  treatment  of  the  highway. 
In  the  attempt  to  beautify  the  roadside,  it  may  be  necessary  to 
sacrifice  a  little  of  utility  to  secure  a  pleasing  effect.  Masses  of  foliage 
and  shade  add  beauty  to  the  roadside,  but  tend  to  keep  the  traveled 
way  damp — usually  the  bane  of  good  earth  roads.  Trees  are  a 
necessary  adjunct  to  a  beautiful  highway,  but  are  anything  but  a 
benefit  to  the  traveled  way.  If  beauty  is  desired  at  the  expense  of 
utility,  highways  can  scarcely  be  too  much  shaded  by  over-arching 
boughs.     However,  a  happy  medium  will  suffice  in  most  places. 

The  varieties  of  trees  suitable  for  the  ornamentation  of  highways 
are  almost  infinite.  The  elm,  with  its  graceful  arching  branches 
and  delicate  lace-like  foliage,  is  not  surpassed;  and  the  hard  maple 


ART.   2.J  MAINTENANCE.  125 

and  the  oaks  are  very  handsome  for  this  purpose.  The  walnut,  the 
butternut,  the  hickory,  the  beech,  the  poplar,  and  the  pine,  ranging 
from  the  most  delicate  to  the  most  somber  and  rugged,  are  all  more 
or  less  adapted  to  particular  requirements  and  circumstances. 
Trees  such  as  willow,  the  roots  of  which  spread  extensively  or  seek 
water,  should  not  be  permitted  to  grow  near  tile  drains,  as  the  small 
roots  frequently  entirely  obstruct  the  tile.  Trees  should  not  be 
planted  close  to  the  traveled  way,  but  near  the  edge  of  the  right  of 
way,  or  if  possible  on  the  private  property  bordering  the  road. 

185.  The  roadside  fences  are  usually  the  property  of  the  adjoin- 
ing land  owner,  and  may  mar  or  beautify  the  landscape.  The 
hedge  rows  of  England  and  the  stone  fences  of  New  England  are  all 
that  can  be  desired  for  appearance,  but  in  localities  where  there  is 
much  snow  they  catch  the  drifting  snow  and  so  obstruct  the  high- 
way. The  only  thing  favorable  to  the  appearance  of  the  common 
wire  fence  is  that  it  is  inconspicuous. 

Art.  2.     Maintenance. 

186.  Proper  maintenance  is  as  important  as  good  construction. 
A  distinction  should  be  made  between  maintenance  and  repairing. 
The  former  keeps  the  road  always  in  good  condition ;  the  latter 
makes  it  so  only  occasionally.  If  the  road  is  not  properly  main- 
tained, it  deteriorates  in  a  geometrical  ratio.  A  small  depression 
fills  with  water  and  soon  becomes  a  mud  hole  which  traffic  makes 
deeper  and  deeper;  or  an  obstructed  side  ditch  forces  the  water  to 
run  down  the  center  of  the  road,  and  gullies  out  the  surface.  A 
defect  which  could  be  remedied  in  the  beginning  with  a  shovelful  of 
earth  or  a  minute's  time,  if  neglected  may  require  a  wagon  load  of 
earth  or  an  hour's  time,  besides  being  in  the  meantime  an  annoyance 
or  a  damage  to  traffic.  The  better  the  state  in  which  a  road  is  kept, 
the  less  are  the  injuries  to  it  by  ordinary  traffic  and  the  weather. 

187.  Destructive  Agents.  Water.  Water  is  the  natural 
enemy  of  good  earth  roads.  The  chief  object  of  maintenance  should 
be  to  keep  the  surface  smooth  and  properly  crowned  so  that  rain 
will  be  shed  into  the  side  ditches.  These  should  be  kept  open  so 
that  the  water  may  be  carried  entirely  away  from  the  road.  This 
subject  is  fully  considered  in  §  194. 


126  EARTH  ROADS.  [CHAP.  III. 

188.  Narrow  Tires.  It  is  desirable  •  that  a  wagon  in  passing 
over  the  road  should  help  to  make  or  preserve  it,  and  not  to  destroy 
it;  and  therefore  as  far  as  the  road  is  concerned,  within  reason- 
able limits,  the  broader  the  tire  the  better. 

"The  matter  of  width  of  tires  has  been  a  subject  of  much  remark. 
There  has,  indeed,  been  no  end  of  idle  talk  concerning  this  matter, 
much  of  it  directed  to  the  point  that  our  American  wagon-builders 
have  shown  a  lack  of  judgment  in  building  with  narrow  tires,  while 
they  should  provide  their  vehicles  with  broad  treads  such  as  are  in 
use  in  Europe.  The  fact  is  that  in  this,  as  in  many  other  ways  in 
which  our  people  have  departed  from  ancient  and  old-world  cus- 
toms, they  have  been  led  by  wisdom  and  not  by  folly.  This  will  on 
a  little  consideration  be  made  evident.  Where  there  is  no  definite 
pavement,  as  in  ninety-nine  hundredths  of  the  mileage  of  American 
roads,  the  wheels  have  in  muddy  weather  to  descend  into  the  earth 
until  they  find  a  firm  foundation  on  which  to  rest.  In  so  doing  they 
have  to  cleave  sticky  mud  which  often  has  a  depth  of  a  foot  or  more. 
If  these  wheels  were  broad-tired,  the  spokes  would  also  have  to  be 
thick  and  the  felloes  wide,  so  that  the  aggregate  holding  power  of 
the  mud  upon  the  vehicle  would  be  perhaps  twice  what  it  is  at  pres- 
ent. It  is  useless  to  talk  about  the  advantages  of  a  broader  xread 
to  the  wheels  of  our  wagons  until  we  have  a  thoroughly  good  system 
of  roads  which  they  are  intended  to  traverse.  Any  laws  looking  to 
this  end  would  be  disobeyed  because  of  private  needs  so  general 
that  they  would  amount  to  a  public  necessity.  When  the  roads  of 
a  district  are  made  good  only  as  to  the  main  lines  of  communication, 
the  side  roads  and  the  farms  still  demand  the  peculiar  advantages 
afforded  by  the  narrow  tire."  * 

Tables  4  and  5,  pages  24  and  25,  show  that  under  some  condi- 
tions the  narrower  tire  requires  less  tractive  power  than  the  wider 
tire,  which  supports  the  claim  in  the  above  quotation. 

Although  there  is  not  much  difference  between  the  tractive 
power  of  broad  and  narrow  tires,  the  latter  are  much  more  destruc- 
tive on  any  road,  particularly  on  an  earth  one;  but  in  deciding  upon 
the  proper  width  of  tire,  there  are  other  factors  besides  the  road  that 

♦American  Highways,  N.  S.  Shaler,  Dean  of  Lawrence  Scientific  School,  Harvard 
University,  and  formerly  President  of  the  Massachusetts  Highway  Commission. 
p.  163-4. 


ART.  2.]  MAINTENANCE.  127 

must  be  considered.  If  wagons  were  employed  only  upon  the  public 
highway,  it  might  be  wise  to  use  wide  tires  and  sacrifice  some  trac- 
tive power  for  the  benefit  of  the  roads.  Other  things  being  equal, 
a  wagon  with  broad  tires  is  not  so  easily  managed  as  one  with  nar- 
row tires.  To  be  equally  easy  to  turn,  the  broad-tired  wagon 
should  have  the  narrower  bed,  or  the  longer  front  axle,  or  the 
smaller  front  wheel.  In  Europe  it  is  customary  to  adopt  the 
smaller  front  wheel,  which  is  very  destructive  of  the  broken-stone 
roads  so  common  in  that  country.  Increasing  the  length  of  axle 
interferes  with  getting  the  wagon  up  to  cribs,  warehouses,  etc.,  and 
increases  the  difficulty  in  going  through  gates,  passing  buildings,  and 
the  like,  and  hence  it  is  not  clear  that  laws  should  be  passed  regu- 
lating the  width  of  tires,  many  claims  to  the  contrary  notwithstand- 
ing. 

"The  best  argument  against  the  enactment  of  laws  concerning 
broad  tires  is  found  in  the  fact  that  the  numerous  and  long-enforced 
English  statutes  on  this  matter  have  of  late  years  been  abrogated, 
a  century  of  experience  having  shown  that  they  are  difficult  to 
administer  and  generally  disadvantageous."  *  The  Massachusetts 
Highway  Commission,  after  an  elaborate  discussion  of  the  subject,! 
says:  "It  is  a  matter  of  doubtful  expediency  to  endeavor,  in  the 
present  state  of  our  highways,  by  general  legislation  to  control  the 
width  of  tires  or  the  diameter  of  wheels." 

It  is  probably  best  to  leave  the  matter  to  private  individuals 
and  the  enterprise  of  manufacturers.  The  matter  should  at  least 
be  left  to  local  authorities  to  pass  regulations  which  shall  be  suited 
to  their  particular  conditions.  Several  states  and  cities  have  laws 
regulating  the  width  of  tires,  but  it  does  not  appear  that  broad  tires 
are  any  more  common  there  than  in  localities  where  no  such  laws 
exist. 

189.  Many  European  countries  have  laws  regulating  the  width 
of  tires.  In  England  for  100  years  the  law  required  1  inch  of  tire 
for  each  500  pounds  of  load,  but  all  laws  regulating  the  width  of 
tires  have  been  repealed.  In  France  the  tires  of  market  carts  vary 
from  3  to  10  inches  in  width,  being  generally  from  4  to  6  inches, 


*  Shaler's  American  Highways,  p.  165. 

f  Report  of  the  Massachusetts  Highway  Commission  for  1893,  p.  56-62. 


128  EARTH    ROADS.  [(HAP.    III. 

with  the  rear  axle  about  14  inches  longer  than  the  forward  one. 
In  Bavaria  the  legal  width  is  as  follows : 

Minimum  width  of  tires  of  2-wheeled  carts,  with  2  horses,  4.13  inches 

«       u     «     «   2-wheeled      "        "     4     I"  6.18      " 

"       "     "      u  4-wheeled wagons, "     2       "  2.60      " 

"       "     "      "  4-wheeled       "        "     3  or  4  horses,  4.13      " 
"       "     "      "4-wheeled       "        "     5  to  8       "        6.18      " 

In  this  country  a  number  of  the  states  have  statutes  concerning 
the  width  of  tires,  many  of  which  take  the  form  of  a  rebate,  either 
cash  or  part  of  the  road  tax,  to  those  using  tires  of  a  prescribed 
width.     The  following  is  the  legal  width  in  Ohio: 

Minimum  width  of  tire  for  load  of  2,500  to  3,500  pounds 3    inches 

"       "     "     "      "      "  3,500  "  4,000      "         3*       " 

"  "       "     "     «     "      '.'  4,000  "  6,000      "  4         " 

"       "     "     "      "      "6,000'"   8,000      "         5         " 

"       "     "     "      "      "  8,000  or  more       "         6 

According  to  wagon  manufacturers  about  60  per  cent  of  the 
wagons  used  on  country  roads  have  tires  1^  to  If  inches  wide,  those 
of  the  remaining  40  per  cent  being  2  to  4  inches.  The  broad  tire  is 
of  comparatively  recent  introduction  on  rural  roads  in  this  country. 

190.  In  some  respects  the  injury  by  narrow  tires  is  greater  on 
broken-stone  roads  than  on  earth  roads,  since  the  damage  can  be 
more  readily  repaired  in  the  latter  than  in  the  former;  but  even  on 
a  broken-stone  road,  there  is  a  limit  beyond  which  it  is  not  wise  to 
increase  the  width  of  the  tire.  The  crown  of  the  road  is  such  that 
the  point  of  contact  with  the  road  is  at  one  edge  of  the  tire,  and  it  is 
generally  conceded  that  no  material  advantage  is  gained  in  making 
the  tire  more  than  4  or  5  inches  wide. 

191.  Equal  Axles.  Since  the  hind  wheel  follows  in  the  track  of 
the  fore  wheel,  it  increases  the  depth  of  the  rut,  and  consequently 
increases  the  destructive  effect  of  the  wagon  upon  the  road.  The 
remedy  would  be  to  make  the  lengths  of  the  two  axles  unequal,  but 
this  would  make  the  wagon  more  difficult  to  manage  and  would 
also  increase  the  tractive  resistance.  The  advantage  of  not  per- 
mitting one  wheel  to  exactly  follow  another,  is  shown  by  the  fact 
that  there  are  no  ruts  at  a  corner  or  a  sharp  turn  in  the  road;  but 
it  is  not  practicable  to  secure  this  advantage  generally,  either  by 


ART.  2.]  MAINTENANCE.  129 

making  the  two  axles  of  unequal  length  or  by  preventing  a  wagon 
from  traveling  in  the  ruts  already  made. 

f  192.  Small  Wheels.  The  smaller  the  wagon  wheels  the  greater 
the  destructive  effect  upon  the  road,  and  also  the  greater  the  trac- 
tive power  required;  but  for  ease  of  loading  and  convenience  of 
management,  low  wheels  are  better  than  high  ones.  It  is  probably 
wise  to  permit  those  who  use  the  wagons  and  the  roads,  and  pay 
for  both — usually  the  farmers — to  determine  the  most  economic 
diameter  of  wheels. 

The  wagons  in  ordinary  use  on  country  roads  have  three  sizes  oi 
wheels,  as  follows,  for  the  front  and  the  rear  wheels  respectively: 

3  feet  2  inches  and  3  feet  8  inches 
3    "6      "      and  3    "  10      ". 
3    "    6      "      and  4    "    6      " 

According  to  wagon  manufacturers  about  80  per  cent  of  the  wagons 
on  the  country  roads  have  the  last-named  size  of  wheels. 

193.  Horse  not  Hitched  Before  Wheel.  On  broken-stone  roads, 
the  horses'  feet  loosen  fragments  of  stone,  which  tends  to  destroy 
the  surface ;  and  if  the  horses  were  hitched  directly  in  front  of  the 
wheels,  the  stones  loosened  by  the  horses'  feet  would  be  rolled  down 
by  the  wheels  of  the  wagon.  This  is  a  matter  of  some  moment  with 
broken-stone  roads,  but  is  hardly  practicable  with  earth  roads. 
However,  some  teamsters  hitch  their  horses  in  front  of  the  wheel,  to 
enable  their  horses  and  wheels  to  run  in  the  beaten  track  made  by 
the  feet  of  preceding  horses  not  hitched  in  front  of  the  wheel. 

194.  CARE  OF  THE  SURFACE.  The  most  important  work  in 
maintaining  an  earth  road  is  to  keep  the  surface  smooth  so  that  the 
rain  water  will  flow  quickly  into  the  side  ditches.  If  the  surface  of 
the  roadway  is  properly  formed  and  kept  smooth,  the  water  will  be 
shed  into  the  side  ditches  and  do  comparatively  little  harm ;  but  if  it 
remains  upon  the  surface,  it  will  be  absorbed  and  convert  the  road 
into  mud.  If  all  ruts,  depressions,  and  mud  holes  are  not  filled  as 
soon  as  they  appear,  they  will  retain  the  water  upon  the  surface,  to 
be  removed  only  by  gradually  soaking  into  the  road-bed  and  by 
slowly  evaporating;  and  each  passing  wheel  or  hoof  will  help  to 
destroy  the  road. 

There  are  several  machines  or  devices  which  are  very  effective 


130  EARTH    ROADS.  [CHAP.   III. 

in  filling  ruts  and  depressions,  and  in  keeping  the  surface  smooth. 
Different  tools  are  best  under  different  conditions.  These  tools 
and  the  method  of  using  them  will  be  considered  briefly. 

195.  Harrow.  In  the  winter  there  frequently  come  times  when 
the  road  is  full  of  holes  and  ruts,  while  the  surface  soil  is  dry  and' 
mellow.  This  condition  occurs  most  frequently  when  the  ground 
below  the  surface  is  frozen.  If  at  this  time  a  harrow  is  run  over 
the  road,  it  will  fill  up  the  ruts  and  holes  and  leave  the  surface  com- 
paratively smooth.  This  improves  the  road  for  present  travel,  and 
gives  a  smooth  surface  which  will  greatly  decrease  the  deterioration 
of  the  road  by  subsequent  rains.  The  ordinary  adjustable  farm 
harrow  should  be  used,  and  the  teeth  should  be  set  to  slope  well 
back.  The  labor  required  is  not  great,  since  a  12-foot  harrow 
can  be  used,  and  then  a  single  round  is  sufficient. 

Often  there  are  only  a  few  hours  in  the  middle  of  the  day  when 
the  frost  is  out  of  the  ground  sufficiently  to  permit  this  work  to  be 
done,  and  therefore  it  is  best  for  each  farmer  to  harrow  the  road 
adjoining  his  own  land  (see  paragraph  3  of  §  46).  The  work  comes 
at  a  season  of  year  when  the  farmer's  time  is  usually  not  very 
valuable,  and  hence  the  expense  is  small.  This  method  of  treating 
earth  roads  has  proved  very  beneficial  both  in  securing  good  roads 
and  in  preserving  them. 

In  the  summer,  when  the  roads  get  roughed  up,  they  can  be 
materially  improved  at  small  expense  by  running  over  them  with 
a  harrow  having  the  teeth  down  quite  flat.  If  the  roads  are  a 
little  muddy,  this  treatment  will  make  them  dry  faster  and  also 
make  them  much  more  pleasant  to  use  after  they  have  dried. 

196.  Railroad  Rail.  In  the  early  spring,  just  after  the  frost 
goes  out  of  the  ground,  earth  roads  are  usually  full  of  deep  ruts. 
The  harrow  is  not  suitable  for  the  work  now  required.  The  object 
is  simply  to  cut  off  the  ridges  and  fill  up  the  ruts,  and  thus  "  break 
the  way  "  for  travel.  It  is  well  to  break  the  road  early  in  the  season, 
both  to  accommodate  immediate  travel  and  to  hasten  the  coming 
of  a  better  condition  of  the  road.  It  is  much  more  economical  to 
make  the  road  smooth  with  a  machine  than  to  wear  it  down  by 
travel. 

There  are  many  road  machines  on  the  market,  all  of  which  are 
most  excellent  for  certain  kinds  of  work  to  be  referred  to  later,  but 


AST.   2.]  MAINTENANCE.  131 

most  of  which  are  too  heavy  for  the  conditions  just  described.  Most 
of  the  machines  are  mounted  upon  four  wheels,  and  of  themselves  are 
a  considerable  load  over  roads  which  are  only  a  succession  of  ridges, 
ruts,  and  mud  holes;  and  are  heavier  and  more  cumbersome  than  is 
necessary  for  the  work  now  under  consideration. 

197.  A  railroad  rail  14  to  16  feet  long  drawn  by  two  two-horse 
teams  has  been  used  with  great  success  in  breaking  down  the  ridges 
and  filling  up  the  ruts.  The  team  is  hitched  to  an  eye  fastened 
through  the  web  2  or  3  feet  from  the  end  of  the  rail.  The  edge  of 
the  base  of  the  rail  serves  as  a  cutting  edge.  A  7-inch  steel  I-beam 
is  equally  good. 

When  the  ground  is  mellow  and  loose  after  freezing  and  thawing, 
the  steel  rail  will  smooth  the  road  nearly  as  satisfactorily  as  the 
scraping  grader  (§  142)  and  much  more  rapidly,  since  it  cuts  a  wider 
swath  and  since  the  draft  is  so  light  that  the  teams  walk  right  along. 
One  round  trip  is  usually  sufficient  for  any  road.  The  time  when 
the  work  is  most  advantageously  done  is  comparatively  limited, 
and  therefore  one  rail  should  not  be  expected  to  cover  too  much 
road.  The  cost  is  so  small  that  one  can  be  provided  for  each  few 
miles  of  road, — the  number  depending  upon  the  nature  of  the  soil 
and  the  climate.  If  roads  are  treated  in  this  way,  they  will  not  get 
so  rough;  and  hence  will  require  less  work  later  with  the  heavy 
road  machine. 

198.  Light  Scrapers.  A  heavy  stick  of  timber  faced  on  one 
side  with  a  steel  plate,  and  hitched  behind  a  wagon  or  drawn  by  a 
team  direct,  is  very  effective  in  smoothing  the  way  for  travel.  To 
the  top  face  of  the  timber  should  be  fastened  a  frame  by  which  to 
hitch  the  leveler  to  the  wagon  or  team.  This  frame  should  be  in  the 
form  of  a  capital  A  with  one  leg  a  little  shorter  than  the  other,  to 
cause  the  cutting  edge  to  stand  obliquely  to  the  line  of  draft. 

Fig.  37,  page  132,  shows  a  slightly  more  elaborate  form  of  road 
leveler.  The  blade  is  usually  about  }  inch  thick,  4  inches  wide,  and 
72  inches  long.  The  timber  is  6X12  inches  square  by  6  feet  long. 
This  form  costs  $10  to  $12. 

Fig.  38,  page  132,  shows  a  still  more  elaborate  form  of  road 
leveler.  The  blade  is  all  steel,  and  may  be  tilted  forward  or  back- 
ward.    The  catalogue  price  of  this  machine  is  $50. 

199.  The  advantage  of  these  scrapers  or  road  levelers  is  that 


132 


EARTH  ROADS. 


[CHAP.  III. 


they  are  cheap,  and  are  easily  handled.     They  do  a  little  better 
work  than  the  railroad  rail,  but  their  first  cost  and  cost  of  operation 


Fig.  38. — Detroit  Road  Levklkb. 

is  considerably  more ;  and  they  are  not  as  effective  as  the  four-wheel 
scraping  grader,  but  their  first  cost  is  much  less  and  they  are  easier 
handled.  They  are  not  effective  when  the  road  is  very  rough  or 
very  hard. 

200.  Two-wheel  Scrapers.  There  are  several  two-wheel  road 
scrapers  upon  the  market,  of  which  Fig.  39,  page  133,  is  the  most 
elaborate.  The  blade  of  this  machine  is  adjustable  in  both  the 
horizontal  and  the  vertical  plane,  and  can  be  raised  and  lowered. 
The  wheels  can  be  inclined  to  neutralize  the  resistance  of  the  furrow 
to  being  moved  laterally;  in  other  words,  the  oblique  wheels  pre- 
vent the  whole  machine  from  sliding  sidewise. 

The  other  two-wheel  machines  consist  virtually  of  the  blade  of 
the  scraping  grader  (§  142)  carried  on  a  pair  of  high  wheels,  and  are 
the  results  of  an  attempt  to  supply  a  cheaper  machine  than  the  four- 
wheel  scraping  grader. 

201.  No  two-wheel  scraper  can  do  as  good  work  as  the  four-wheel 


ART.  2.] 


MAINTENANCE. 


133 


machine  shown  in  Fig.  24,  25,  and  34,  pages   102   and  109,  since 
the  long  frame  with  four  points  of  support  gives  a  more  uniform 


Fig.  39. — Kennett-Square  Road  Leveler. 

surface  to  the  road,  and  since  the  blade  of  the  two-wheel  machine 
has  a  tendency  to  work  into  or  out  of  the  ground  and  thus  form 
scallops  in  the  surface  of  the  road. 

202.  Scraping  Grader.  In  late  spring,  after  the  ground  has 
settled,  roads  should  be  prepared  for  summer  travel  by  being  shaped 
up  with  the  scraping  grader  (§  142).  When  this  work  is  to  be 
done,  the  ground  is  comparatively  dry,  and  consequently  the 
heavy  scraping  grader  is  required  and  can  be  handled  on  the  roads. 
It  is  somewhat  unfortunate  that  this  tool  is  ordinarily  called  a  road 
grader,  since  the  name  has  possibly  led  to  a  misconception  as  to 
an  important  use  of  the  machine.  As  an  instrument  of  road  con- 
struction, this  machine  is  used  to  give  a  crown  to  the  road;  but  as 
an  instrument  of  maintenance,  it  should  be  used  only  to  smooth 
the  surface  and  restore  the  original  crown.  Apparently  some 
operators  assume  that  the  machine  is' not  to  be  used  except  to  in- 
crease the  crown  of  the  road;  at  least  since  the  introduction  of  this 
road  machine  there  has  developed  a  strong  tendency  to  increase 
the  crown  unduly.  Side  slopes  steeper  than  just  enough  to  turn 
the  water  into  the  side  ditches  are  a  detriment.  Other  things 
being  equal,  the  best  road  to  travel  on  or  to  haul  a  load  over  is  a 
perfectly  flat  one. 

203.  Operating  the  Scraping  Grader.  To  smooth  the  road,  the 
machine  should  be  run  over  the  ground  so  as  to  plane  off  the  ridges 
and  fill  up  the  ruts.     Commence  at  the  ditch  and  work  toward  the 


134  EARTH    ROADS.  [CHAP.   III. 

center,  scraping  with  the  entire  length  of  the  blade.  The  blade 
should  stand  nearly  square  across  the  road,  and  considerable 
earth  should  be  shoved  along  in  front, — enough  to  fill  the  depres- 
sions ; — but  only  enough  earth  should  be  moved  toward  the  center  of 
the  roadway  to  re-place  that  washed  down  by  the  rains.  The  sur- 
plus earth  should  be  uniformly  distributed  along  the  surface,  by 
carrying  the  rear  end  of  the  blade  a  little  higher  than  the  point.  A 
ridge  of  earth  should  not  be  left  in  the  center  of  the  road,  since  it 
will  only  slowly  consolidate  and  is  likely  to  be  washed  into  the  side 
ditches  to  make  trouble  there. 

This  work  should  be  done  early — before  the  ground  becomes 
hard  and  difficult  to  work,  before  traffic  has  been  compelled  par- 
tially to  do  the  work  of  the  road  leveler,  and  while  the  surface  is  in 
condition  to  unite  with  the  loose  earth  left  by  the  machine,  and 
when  the  roots  of  grass  and  weeds  do  not  interfere  with  the  work  of 
the  blade.  Unfortunately  this  work  is  often  postponed  until  the 
ground  is  so  hard  that  it  is  impossible  to  do  a  thoroughly  good  job. 
If  the  ground  is  a  little  too  wet  for  tillage,  it  is  all  the  better  for 
road  making,  since  it  will  pack  and  harden  better  than  though  it 
were  drier.  After  the  ground  becomes  dry  and  hard,  it  is  not  only 
more  laborious  and  expensive  to  secure  a  smooth  surface;  but  the 
newly  repaired  road  may  for  weeks  be  in  a  worse  condition  than 
before  it  was  worked,  since  the  loose  earth  is  too  dry  to  pack  under 
traffic. 

If  during  the  summer  the  road  becomes  badly  rutted,  the  scrap- 
ing grader  should  be  lightly  run  over  the  surface — preferably  when 
the  road  is  a  little  damp.  A  little  timely  work  done  in  the  right 
way  is  like  "the  stitch  in  time  that  saves  nine." 

204.  A  common  error  in  scraping  roads  is  not  to  begin  far  enough 
down  in  the  ditch,  thus  leaving  a  shoulder  which  prevents  the  water 
from  flowing  from  the  roadway  into  the  side  ditch.  Fig.  40  shows  a 
road  finished  in  this  way.  The  shoulders  not  only  dam  back  the  water, 
but  also  narrow  the  roadway;  and  after  weeds  and  grass  have  got 
a  good  start,  it  is  improbable  that  the  shoulder  will  be  cut  off  next 
time  the  road  is  scraped,  and  in  all  probability  each  successive 
scraping  will  make  a  bad  matter  worse.  However,  with  a  skilful 
use  of  the  scraping  grader  these  shoulders  can  be  cut  off  (see  Fig.  31. 
page  107). 


ART.   2.]  MAINTENANCE.  135 

205.  Not  infrequently  writers  claim  that  material  from  the  side 
ditches  should  not  be  placed  upon  the  roadway.  Unquestionably 
silt  from  the  bottom  of  the  ditches  is  undesirable  material  with 
which  to  build  or  repair  a  road;  but  in  ditches  properly  constructed 
and  cared  for,  there  is  not  much,  if  any,  of  such  material,  and  if  any 
of  it  is  removed  with  the  scraping,  grader  it  is  so  thoroughly  mixed 
with  good  material  before  it  reaches  the  roadway  as  to  be  practi- 
cally harmless.  The  advice  against  fine  material  from  the  side 
ditches  originated  when  the  drag  scraper  was  the  chief  tool  used  in 


Fig.  40. — Objectionable  Shoulders  Left  by  Scraper. 

repairing  roads,  and  the  advice  has  unfortunately  outlasted  its 
usefulness. 

206.  Cost  of  Scraping.  To  shape  up  the  road  in  the  spring, 
six  horses  and  three  men  are  required  to  operate  the  scraper.  The 
wages  of  a  team  and  driver  will  usually  be  $3.00  or  $3.50  per  day, 
since  generally  the  scraping  should  be  done  when  farmers  are  busy 
with  farm  work,  and  since  the  work  is  hard  on  teams.  The  cost  of 
operating  the  grader  is  then  $9.00  to  $10.50  per  day.  A  scraper  will 
on  the  average  smooth  up  3  or  4  miles  per  day,  at  an  expense  of 
$3.00  to  $3.50  per  mile,  or,  in  round  numbers,  including  repairs  and 
loss  by  bad  weather,  say,  $4.00  per  mile.  If  the  road  is  not  very 
rough  two  rounds  are  enough,  and  if  it  is  very  bad  four  may  be 
required,  but  on  the  average  three  rounds  are  sufficient.  If  the 
work  is  postponed  too  long,  the  cost  may  be  nearly  double  the  above. 
Not  infrequently  a  traction  engine  can  be  hired  cheaper  than  horses ; 
and  if  the  roads  are  not  too  rough  or  too  soft,  the  engine  is  better 
than  horses. 

The  cost  of  smoothing  up  city  streets  would  be  considerably 
more  than  the  above,  because  of  the  time  consumed  in  passing  side- 
walk crossings  or  in  turning  to  avoid  them.  However,  the  amount 
of  work  accomplished  in  a  day  depends  greatly  upon  the  training  of 
men  and  horses.  In  a  particular  case,  city  teams  were  employed 
to  scrape  city  streets,  and  with  every  appearance  of  an  honest 
effort  only  fifteen  blocks  were  shaped  per  day.     Under  the  same 


136  EARTH    ROADS.  [CHAP.   III. 

conditions,  country  teams  smoothed  twenty-five  blocks  per  day 
with  seemingly  no  unusual  effort. 

207.  The  actual  cost  for  country  roads  is  often  much  greater 
than  the  above,  particularly  when  the  work  is  done  under  the  road- 
tax  system,  since  frequently  when  the  operator  is  ready  to  work  he 
must  go  several  miles  for  the  grader  and  then  finds  that  it  is  in  use 
or  is  somewhere  else;  and,  perhaps,  when  found  he  discovers  that 
the  blade  must  be  taken  to  the  blacksmith-  shop  to  be  sharpened. 
The  remedy  for  this  state  of  affairs  is  in  better  road  administration 
and  in  having  more  machines.  The  number  of  miles  of  road  which 
one  machine  will  serve  will  depend  upon  the  nature  of  the  soil,  the 
amount  of  travel,  the  condition  in  which  the  roads  are  kept,  the 
amount  of  use  made  of  the  harrow  (§  195)  and  of  the  railroad  rail 
(§  196),  and  upon  whether  the  roads  are  maintained  under  the 
labor-tax  or  the  cash-tax  system  (§  52).  On  the  prairie  of  the 
Illinois  corn-belt  one  machine  is  sufficient  for  15  to  25  miles  of  road. 

208.  Rolling.  Many  writers  recommend  the  use  of  a  roller  in 
maintaining  earth  roads.  Unquestionably  the  more  compact  the 
road-bed  the  better,  but  the  advantage  secured  by  rolling  is  not 
worth  the  cost.  The  only  time  when  a  roller  would  have  an  appre- 
ciable effect  would  be  early  in  the  spring,  just  after  the  frost  has 
gone  out  of  the  ground;  but  clearly  it  would  be  impracticable  to 
use  the  roller  before  the  surface  has  been  smoothed  with  the  scrap- 
ing grader;  and  after  the  surface  has  been  smoothed  up  by  planing 
off  the  ridges  and  filling  up  the  hollows,  the  roller  would  simply 
ride  on  the  ridges  and  practically  not  compact  the  road  at  all — at 
least  not  where  most  needed,  i.  e.,  in  the  hollows.  It  is  not  known 
that  the  roller  was  ever  tried  in  maintenance — at  least  several 
writers  who  have  recommended  it  highly  for  this  purpose  say  that 
they  do  not  know  of  its  ever  having  been  so  used.     See  §  130. 

209.  Filling  Holes.  After  the  road  has  been  smoothed  by  the 
scraping  grader,  it  is  a  good  plan,  particularly  if  the  road  is  very 
rough,  to  send  a  man  with  a  shovel  to  fill  up  all  ruts  and  depressions 
that  were  too  deep  to  be  filled  by  the  scraper.  The  cost  is  small, 
but  the  benefit  is  very  great.  If  a  deep  hole  has  been  filled  by  the 
scraper,  it  is  well  to  add  a  little  more  earth  to  provide  for  settlement 
in  order  to  prevent  the  re-appearance  of  the  hole.  The  new  mate- 
rial should  be  trodden  or  tamped  solidly  into  place. 


A.RT.   2.]  MAINTENANCE.  137 ' 

Holes  and  ruts  in  an  earth  road  should  never  be  filled  with  stone, 
brick,  or  coarse  gravel.  The  hard  material  does  not  wear  uniform 
with  the  rest  of  the  road,  but  produces  bumps  and  ridges,  and 
usually  results  in  making  two  holes,  each  larger  than  the  original 
one.  It  is  a  bad  practice  to  cut  a  gutter  from  a  hole  to  drain  it  to 
the  side  of  the  road.  Filling  the  hole  is  the  proper  course,  whether 
it  is  dry  or  contains  mud. 

If  the  scraper  has  left  any  shoulders  next  to  the  side  ditches 
(see  204),  they  should  be  carefully  removed  with  the  shovel.  Fre- 
quently there  are  holes  at  the  end  of  bridges  and  along  the  side  of 
small  wood-box  culverts  which  require  attention.  Finally,  during 
the  fall  the  roads  should  be  repaired  with  special  reference  to  getting 
them  into  good  shape  for  the  winter.  Any  saucer-like  depressions 
or  ruts  should  be  filled  with  earth  like  that  of  the  road-bed. 

210.  Removing  Stones.  Bumping  along  over  stones  is  hard 
upon  the  rider's  back,  a  strain  upon  the  vehicle,  trying  on  the  team, 
and  damaging  to  the  road.  All  loose  stones  larger  than  one  inch, 
or  at  most  two  inches,  in  diameter  should  be  taken  entirely  away 
or  be  piled  beyond  the  side  ditches;  and  stones  projecting  above  the 
surface  should  be  dug  out.  Usually  the  stones  can  be  removed 
with  comparative  ease.  They  should  never  be  left  just  outside 
of  the  trackway,  as  is  sometimes  done,  to  restrict  traffic  and  to 
obstruct  the  flow  of  water  from  the  center  to  the  side  ditches. 

Not  a  few  inhabitants  of  towns  and  villages  consider  it  legiti- 
mate to  throw  brickbats  and  stones  from  their  yards  into  the  street. 
This  practice  deserves  severe  condemnation.  Many  streets  could 
be  materially  improved  at  small  expense,  both  in  appearance  and' 
for  travel,  by  the  removal  of  all  stones  and  bricks. 

211.  CARE  OF  SIDE  DITCHES.  The  side  ditches  should  be  ex- 
amined in  the  fall  to  see  that  they  are  free  from  dead  weeds  and 
grass;  and  late  in  the  winter  they  should  be  examined  again  to  see 
that  they  are  not  clogged  with  corn  stalks,  brush,  etc.,  washed  in 
from  the  fields.  The  mouth  of  culverts  should  also  be  cleared  of 
rubbish,  and  the  outlet  of  tile  drains  should  be  opened.  Attention 
to  side  ditches  will  prevent  overflow  and  washing  of  the  road-bed, 
and  will  also  prevent  the  formation  of  ponds  at  the  roadside  and 
the  consequent  saturation  of  the  road-bed.  The  road  care-taker 
should  frequently  go  over  his  portion  of  the  road  just  as  a  heavy 


138  EABTH    ROADS.  [CHAP.   III. 

fall  of  snow  is  going  off,  for  it  is  then  that  the  most  damage  is  done 
by  water. 

212.  CARE  OF  ROADSIDE.  It  is  desirable  that  the  roadside 
should  be  so  cared  for  as  to  secure  a  coating  of  grass  instead  of  un- 
sightly and  noxious  weeds.  This  can  usually  be  accomplished  with 
an  occasional  mowing  with  but  slight  expense. 

213.  Care  of  Trees  and  Hedges.  Earth  roads  should  have 
plenty  of  light  and  air.  Trees  along  the  road  may  add  beauty  to 
the  landscape  (§  184),  but  shade  is  nearly  sure  to  breed  mud  holes. 
In  some  localities  and  under  some  conditions,  shade  upon  the  road 
surface  should  be  practically  eliminated  by  cutting  down  the  trees 
or  by  trimming  them  so  as  not  to  keep  the  breeze  and  sunlight  from 
the  road;  but  in  other  localities  and  under  other  conditions,  a  little 
of  the  utility  of  the  road  may  be  sacrificed  to  secure  attractiveness 
in  the  general  surroundings. 

A  tall  hedge  cuts  off  the  view  of  the  adjacent  country,  shuts  out 
the  breeze,  in  a  dry  time  keeps  in  the  dust,  and  in  a  wet  time  retards 
the  drying  of  the  road.  The  hedges  usually  belong  to  the  adjacent 
private  property,  but  in  most  states  the  height  is  limited  by  statute; 
and  in  such  cases  the  road  officials  should  enforce  the  law.  If  there 
is  no  law  governing  hedges  and  trees  near  the  road  on  private 
property,  the  road  officials  should  use  all  possible  diplomacy  to  have 
trees  and  hedges  trimmed  with  reference  to  the  benefits  of  the  road. 
In  this  connection,  see  §  214. 

214.  Obstruction  by  Snow.  In  localities  subject  to  heavy 
falls  of  snow,  it  is  an  important  matter  to  keep  the  roads  from  be- 
coming obstructed  by  it  during  the  winter.  In  some  countries  where 
there  is  only  an  occasional  fall  of  snow,  as  in  France,  it  is  customary 
to  remove  it  from  the  surface  of  the  road ;  but  where  there  is  much 
snow,  it  is  only  necessary  to  compact  it  so  as  to  make  the  road  pass- 
able. This  is  done  by  driving  horses  or  cattle  back  and  forth  along 
the  road,  or  by  rolling  the  road  with  a  heavy  farm-roller.  The  use 
of  the  roller  should  commence  with  the  first  storm  of  the  season  and 
be  continued  as  often  as  necessary  through  the  winter.  In  the  case 
of  a  very  heavy  storm,  the  roller  should  be  sent  over  the  roads  at 
intervals  during  its  continuance.  Obviously  this  work  must  be 
done  by  the  residents  along  the  road. 

Snow  and  ice  frequently  accumulate  in  the  side  ditches  to  such  a 


ART.   2.]  MAINTENANCE.  139 

height  as  to  make  the  surface  of  the  road  the  principal  line  of  drain- 
age. In  the  spring,  when  this  occurs  on  earth  roads,  a  large  volume 
of  snow-water  flows  down  the  road,  and  often  seriously  damages  it 
by  washing  gullies  in  the  surface.  Even  the  best  broken-stone 
roads  may  be  seriously  injured  in  this  way;  and  in  some  localities 
it  is  necessary  to  remove  the  snow  from  the  side  ditches  to  prevent 
damage  of  this  character.  The  difficulty  and  expense  of  keeping 
the  side  ditches  free  from  snow  and  ice  is  greatly  increased,  if  the 
ditches  are  deep  and  narrow,  particularly  since  with  this  form  of 
ditch  it  is  necessary  to  maintain  a  culvert  or  covered  gutter  at  the 
junction  of  cross  roads  and  private  drives  with  the  main  highway. 
These  culverts  are  very  liable  to  become  clogged  with  icy  snow,  and 
it  is  nearly  impossible  to  clear  them  without  digging  them  up — 
which  is  rarely  practicable.  This  difficulty  could  be  obviated,  or 
at  least  greatly  decreased,  by  constructing  shallow  ditches;  and,  if 
necessary,  laying  a  large  tile  drain  under  the  ditch  to  carry  the  sur- 
face water. 

The  cost  of  work  occasioned  by  snow  can  be  decreased  by  proper 
attention  to  the  fences,  underbrush,  etc.,  along  the  side  of  the  road. 
Snow  drifts  are  caused  by  the  obstruction  of  the  currents  of  air  near 
the  ground — those  that  carry  the  drifting  snow.  In  forests  the 
winds  do  not  have  sufficient  velocity  to  carry  the  snow,  and  conse- 
quently it  lies  evenly  and  of  a  uniform  depth;  but  in  the  open 
country  it  drifts  with  the  wind.  Fences  and  shrubbery  which 
retard  the  winds  but  permit  the  snow  to  blow  through,  cause  the 
snow  to  pile  up  on  the  sheltered  side  and  possibly  to  block  the  road 
and  ditches.  The  fences  should  be  either  entirely  open  or  very 
close.  A  high  tight  fence  obstructs  the  wind,  and  causes  the  snow 
to  pile  up  on  the  windward  side.  If  the  roadside  is  partially  ob- 
structed, the  wind  moves  the  loose  snow  into  earth  cuts  and  also 
into  the  beaten  snow  path,  and  fills  them  up.  Filling  the  snow 
trackway  gradually  raises  the  traveled  portion  of  the  road  until 
turning  out  into  the  loose  snow  becomes  dangerous. 

215.  In  Vermont,  "in  many  townships  the  cost  of  keeping  the 
roads  passable  in  the  winter  is  one  third,  and  in  some  one  half,  of 
the  total  amount  expended  on  the  highways,  and  the  average  for 
the  state  is  one  eighth,"  or  $4.30  per  mile  per  annum.* 

*  Report  of  Vermont  Highway  Commissioners,  1896,  p.  17-18,  and  Table  D. 


140  EARTH    ROADS.  [CHAP.   III. 

216.  The  possible  cost  of  maintenance  on  account  of  snow  should 
be  considered  in  locating  a  road  (see  §  93). 

217.  PREVENTION  OF  DUST.  Loam  and  clay  roads  are  im- 
proved by  a  little  moisture — just  enough  to  keep  them  damp  and 
dark  without  making  them  soft  or  spongy.  In  dry  climates  the 
roads  not  only  become  excessively  dusty,  which  is  a  great  discom- 
fort, but  also  wear  into  pot-holes,  which  are  dangerous,  since  being 
filled  level-full  of  dust  their  presence  is  not  revealed  until  a  wheel  or 
a  horse's  foot  plunges  into  them.  In  some  localities  the  dust  at 
times  is  practically  hub  deep,  and  is  not  only  an  annoyance  but 
greatly  increases  the  tractive  resistance.  In  arid  climates  and  even 
in  dry  times  in  humid  climates,  sprinkling  is  an  effective  means  of 
maintenance.,-  A  layer  of  straw  is  sometimes  put  upon  the  road  to 
subdue  or  prevent  the  dust;  but  of  course  the  effect  is  only  tem- 
porary. 

218.  Oiling  the  Road.  Recently  crude  petroleum  has  been 
employed  on  wagon  roads,  instead  of  water,  to  prevent  dust — in 
southern  California  practically,  and  in  several  other  states  experi- 
mentally. Oil  has  been  used  by  a  number  of  railroads  to  reduce 
the  dust  raised  by  trains — particularly  near  passenger  stations. 
When  applied  to  wagon  roads,  oil  reduces  the  dust,  makes  the  road- 
bed at  least  partially  non-absorbent,  and  gives  a  dark-colored  sur- 
face which  is  more  pleasing  to  the  eye  than  the  ordinary  light,  dusty 
soil.  A  further  advantage  gained  from  a  practically  dustless  road 
is  the  prevention  of  dust  upon  fruit  trees  and  upon  park  foliage. 

The  oil  is  applied  preferably  at  a  temperature  of  200°  F.  or  over, 
with  a  sprinkling  wagon.  Oil  should  not  be  applied  to  a  hard  sur- 
face to  prevent  dust,  since  it  is  not  readily  absorbed  and  does  little 
or  no  good.  The  road  should  be  perfectly  dry,  and  the  oil  must  be 
thoroughly  incorporated  with  the  dust.  If  it  is  merely  sprinkled  on 
the  surface,  only  the  top  layer  of  dust  will  be  impregnated;  and  the 
wheels  will  break  up  the  crust  thus  formed  and  expose  the  dust 
below,  and  the  road  will  be  but  little,  if  any,  better  than  before 
treatment.  After  the  oil  has  been  applied,  the  surface  is  stirred 
with  a  light  harrow,  to  mix  the  dust  and  the  oil. 

On  the  sandy  soil  of  southern  California,  the  first  application 

/    usually  consists  of  4,000  to  6,000  gallons  to  a  mile  of  road  16  to  18 

feet  wide,  or  f  to  1^  gallons  per  square  yard.     If  the  surface  is  very 


AKT.  2.]  MAINTENANCE.  141 

loose  more  than  1J  gallons  may  be  required  to  keep  down  the  dust. 
The  rule  is  to  apply  in  the  first  application  all  the  oil  the  read  will 
absorb.  The  road  is  sprinkled  two  or  three  times  during  the  sum- 
mer, the  quantity  of  oil  required  for  the  second  and  third  applica- 
tion being  much  less  than  for  the  first.  The  oil  used  is  the  residuum 
remaining  after  the  naphtha,  gasolene,  and  kerosene  have  been  ex- 
tracted from  crude  petroleum,  and  contains  17  to  18  per  cent  of 
bitumen  (§  570).  The  latter  is  the  most  important  constituent., 
The  oil  costs  in  southern  California  from  $1,00  to  $1.25  per  barrel 
of  42  gallons  f.o.b.  at  the  refinery;  the  outlay  is  about  $200  per 
mile  of  16-foot  trackway  for  three  applications,  of  which  about  $15 
to  $20  is  for  the  labor  necessary  to  apply  the  oil. 

219.  The  application  of  oil  decreases  the  tendency  to  form  mud, 
since  it  aids  the  road  in  shedding  rain  water,  and  also  since  the 
bitumen  in  the  residuum  cements  the  particles  of  the  soil  together 
and  increases  its  resistance  to  being  cut  up  by  traffic.  However, 
the  tendency  of  oil  to  decrease  mud  is  only  slight,  and  the  effect  of 
the  oil  will  not  last  through  a  wet  time.  Oiling  the  road  is  most 
needed  and  is  also  most  effective  in  a  dry  climate.  The  best  results 
are  obtained  on  a  clay  soil  or  on  sandy  or  gravelly  loam ;  and  oil  is 
ineffective  on  fine  sand,  coarse  gravel,  or  alkali  soil. 

Residuum  oil  seems  to  be  very  beneficial  to  macadam  roads 
(see  §  381). 

220.  Cost  of  Road  Maintenance.  In  §  51  are  given  a  few 
data  on  road  expenditures  in  different  states;  and  in  Table  16,  page 
142,  are  details  of  the  expenses  for  roads  in  Champaign  County, 
Illinois.  Notice  that  part  of  the  expenditures  in  Table  16  are  for 
maintenance  proper,  while  part  are  for  improvements  in  the  original 
construction. 

It  is  not  known  that  any  data  similar  to  these  in  Table  16  were 
ever  before  collected,  and  hence  there  is  no  means  of  knowing 
whether  these  data  are  representative.  It  is  probable  that  the  ex- 
penditure for  bridges  is  considerably  larger  than  the  average. 
Champaign  County  is  a  rolling  prairie  situated  in  the  corn  belt. 
There  are  no  large  streams,  and  practically  all  the  land  is  under 
cultivation.  Farm  lands  without  buildings  sell  at  $80  to  $100  per 
acre.  There  are  1.97  miles  of  road  per  square  mile  of  area  outside 
of  cities  and  villages.     All  the  roads  have  a  black  loam  surface. 


142  EAKTH    KOADS.  [CHAP.   III. 

TABLE   16. 
Average  Expenditures  per  Mile  of  Earth  Roads  in  Champaign  Co.,  III. 

1.  New  steel  bridges — exclusive  of  county  aid* $16 .20 

2.  Drainage 6 .  32 

3.  Tile  culverts 1 .  32 

4.  Repairs  of  bridges  and  culverts 2 .  93 

5.  Grading  (not  simply  smoothing  and  leveling) 1 .43 

6.  Smoothing  and  leveling  (not  grading) 2 .83 

7.  Mowing  the  roadsides 1.14 

8.  Administration 2 .  69 

Total $34.86 

221.  ROAD  ADMINISTRATION.  The  condition  and  cost  of  roads 
are  largely  dependent  upon  the  efficiency  of  the  management  of 
road  affairs.  For  a  discussion  of  Road  Administration,  see  §  43-55. 
It  is  believed  that  the  matters  referred  to  in  §  46  are  important 
means  of  stimulating  an  abiding  interest  in  good  roads  and  of  in- 
creasing the  knowledge  of  how  to  construct  and  maintain  them. 

222.  MAINTENANCE  BY  CONTRACT.  In  view  of  the  ordinarily 
inefficient  system  of  caring  for  roads,  it  has  frequently  been  pro- 
posed to  maintain  them  by  contract.  As  a  rule,  work  done  under 
the  supervision  of  a  contractor  who  has  pecuniary  interest  in  the 
result  is  more  economical  than  that  performed  under  the  direction 
of  a  public  official;  but  it  is  not  wise  to  do  work  by  contract  unless 
the  amount  required  can  be  approximately  known  beforehand,  and 
also  unless  the  character  of  the  performance  can  be  easily  deter- 
mined after  completion.  Neither  of  these  important  conditions 
would  be  present  in  a  contract  for  the  maintenance  of  a  public  high- 
way. Owing  to  the  indefiniteness  as  to  the  amount  and  character 
of  the  work  to  be  done,  it  is  not  at  all  certain  that  the  maintenance 
could  be  provided  for  by  contract  for  a  sum  less  than  the  public 
officials  could  do  the  work  under  the  present  system.  The  inspec- 
tion would  finally  depend  upon  the  road  official,  and  the  letting  of  a 
contract  would  increase  the  difficulties  and  expense  of  supervision. 

Under  the  present  system  those  who  perform  the  road  labor 
have  an  interest  in  the  resulting  condition  of  the  roads,  while  the 

*  In  Illinois  the  county  pays  half  the  expense  of  bridges  costing  more  than  a 
specified  per  cent  of  the  assessed  value  of  the  township.  The  expenditures  by  the 
county  for  new  steel  bridges  is  nearly  as  much  as  by  the  township. 


ART.  2.]  MAINTENANCE.  143 

contractor  would  be  interested  only  in  doing  the  work  for  the  least 
money;  and  therefore  the  roads  would  probably  be  worse  under 
the  contract  system  than  under  the  present  system. 

It  is  claimed  that  the  contractor  could  maintain  a  trained  corps, 
and  therefore  do  better  work  than  can  be  obtained  by  the  present 
system.  This  would  possibly  be  true  if  the  amount  of  work  to  be 
done  were  sufficiently  great;  but  the  data  in  Table  16,  page  142, 
shows  that  the  amount  of  work  remaining  to  be  done  by  contract 
is  very  small.  The  expenses  for  bridges  and  drainage  almost  cer- 
tainly represent  contract  work,  and  a  large  part  of  the  expense  for 
"tile  culverts  "  and  for  "  repairs  of  bridges  and  culverts  "  is  formate- 
rial.  These  items  and  the  cost  of  administration  constitute  eight 
tenths  of  the  expenses  reported  in  Table  1 6.  The  remaining  items 
represent  an  expense  for  labor  of  only  about  $6.00  per  mile;  and 
therefore  the  ordinary  expenditure  for  the  care  of  earth  roads  is 
too  small  to  justify  maintaining  a  corps  of  expert  road  workmen. 
Further,  leaving  the  road  work  to  a  comparatively  few  trained 
attendants  would  result  in  a  great  waste  of  time  in  traveling  to  and 
from  the  work.  Again,  the  attendant  would  have  so  many  miles 
of  road  under  his  care  that  he  could  visit  any  particular  piece  only  at 
long  intervals;  and  therefore  could  not  do  the  work  at  the  most 
favorable  time,  and  could  not  become  intimately  acquainted  with 
the  road — conditions  absolutely  necessary  for  proper  maintenance. 
These  objections  have  less  force  as  road  expenditures  increase  and 
as  the  money  is  concentrated  on  a  comparatively  few  roads.  Finally, 
a  large  proportion  of  the  roads  have  an  earth  or  gravel  surface,  and 
the  labor  required  for  their  care  is  similar  to  that  with  which  the 
farmer  is  familiar;  and  therefore  he  is  not  lacking  in  the  skill 
required  in  maintaining  them.  The  farmer  who  travels  a  particular 
road  frequently  and  in  all  kinds  of  weather,  has  a  more  intimate 
knowledge  of  it  than  the  man  who  sees  it  only  occasionally;  and 
therefore  for  this  reason  the  farmer  is  best  able  to  care  for  the  road. 
Besides,  the  farmer  uses  the  road  more  than  anybody  else,  and  he 
alone  pays  for  it.     See  paragraph  3  of  §  46. 

The  system  of  employing  a  man  to  give  his  entire  time  to  the 
road  is  almost  a  necessity  with  first-class  broken-stone  roads,  whose 
maintenance  requires  intimate  knowledge  and  constant  attention, 
but  the  system  is  not  applicable  to  earth  roads. 


144  EARTH  ROADS.  [CHAP.  III. 

Art.  3.     Sand  Roads. 

223.  In  most  localities  roads  on  pure  sand  are  the  worst  in  exist- 
ence, since  they  are  good  only  when  wet,  and  therefore  are  at  their 
worst  most  of  the  year;  while  clay  or  loam  roads  are  at  their  best 
most  of  the  time.  If  the  sand  is  fine,  a  dry  sand  road  is  worse  than 
any  muddy  road. 

224.  DRAINAGE.  Roads  on  pure  or  nearly  pure  sand  require 
very  different  treatment  from  those  on  clay  and  loam.  Dampness 
improves  a  sand  road,  while  it  damages  a  clay  or  loam  road;  and 
therefore  the  preceding  rules  for  the  drainage  of  loam  or  clay  roads 
must  be  reversed  for  sand  roads.  Wet  sand  makes  a  better  road 
than  dry  sand,  and  therefore  draining  a  sand  road  is  useless  and 
possibly  a  damage.  Of  course,  this  is  not  true  of  quicksand,  since 
that  is  improved  by  drainage;  but  there  is  very  little,  if  any,  of 
such  material  in  the  roads. 

225.  GRADING.  Sand  roads  are  usually  nearly  level  longitudi- 
nally and  need  little,  if  any,  grading.  They  should  not  be  crowned, 
since  they  do  not  need  surface  drainage.  The  traveled  portion 
should  be  simply  leveled  off. 

226.  SHADE.  While  shade  harms  a  loam  or  clay  road,  it  im- 
proves a  road  of  sand  or  broken  stone,  since  it  prevents  the  evapo- 
ration of  the  moisture  from  the  road-bed.  Therefore  a  sand  road 
can  be  permanently  improved  by  planting  trees  so  as  to  shade  the 
traveled  way.  They  will  prevent,  in  part,  the  drying  effect  of  the 
winds,  as  well  as  intercept  the  rays  of  the  sun. 

227.  Hardening  the  Surface.  The  great  disadvantage 
of  pure  sand  as  a  road  material  is  the  freedom  with  which  the  grains 
move  one  on  the  other;  and  therefore  to  improve  a  sand  road  grass 
should  be  encouraged  to  occupy  all  the  space  possible,  since  its  roots 
will  decrease  the  movement  of  the  grains  under  the  tread  of  the 
hoofs  and  wheels.  It  is  an  advantage  if  low  growing  bushy  vege- 
tation occupies  the  surface  clear  up  to  the  traveled  way — both  for 
the  shade  and  for  the  binding  effect  of  the  roots  and  the  leaves.  The 
leaves  fall  into  the  ruts  and  also  aid  in  binding  the  sand. 

Where  no  other  recourse  is  possible,  it  is  advantageous  to  have 
two  roadways  adjacent  to  each  other,  one  of  which  is  planted  with 
grass  while  the  other  is  in  use.     If  the  traffic  is  not  very  great  the 


ART.   3  ]  SAND    ROADS.  145 

effect  of  the  grass  will  last  for  a  year  or  two  after  the  road  is  again 
used  by  the  wheels.  A  fertilizer  is  sometimes  applied  to  stimulate 
a  growth  of  grass  upon  the  wheelway.  In  some  localities  the  sand 
is  so  fine  that  it  drifts  like  snow,  and  fills  the  partially  hardened 
way,  in  which  case  the  road  is  improved  by  planting  the  roadsides 
with  grass  to  prevent  the  sand  from  blowing. 

A  road  on  pure  sand  is  improved  .temporarily  by  covering  it 
with  a  thin  layer  of  any  vegetable  fiber,  as  decaying  leaves,  straw; 
marsh  hay,  waste  from  sorghum  mills  (begasse),  fibrous  or  string- 
like shavings,  etc.  This  fibrous  material  soon  becomes  incorporated 
with  the  sand  and  decreases  its  mobility;  but  the  vegetable  matter 
wears  out  and  decays,  and  consequently  the  effect  is  only  temporary. 
The  length  of  time  such  expedients  will  last  depends  upon  the 
climate  and  the  amount  of  travel.  Sand  roads  improved  with 
three  to  four  inches  of  shredded  wood  (excelsior)  have  kept  in 
reasonably  good  condition  for  a  year  or  two. 

The  only  permanent  improvement  possible  for  a  sand  road,  aside 
from  substituting  an  entirely  new  wearing  surface,  is  to  add  a  thin 
layer  of  tough  clay,  and  incorporate  it  with  the  sand — either  by 
traffic  or  with  a  harrow  or  a  corn  cultivator.  This  is  expensive  at 
best,  and  it  is  difficult  to  get  the  sand  and  clay  thoroughly  incor- 
porated in  the  right  proportions;  but  the  result  is  permanent. 

228.  In  this  connection  it  is  a  significant  fact  that  the  sand 
shoulders  of  a  broken-stone  road  soon  become  firm  and  hard,  owing 
to  the  infiltration  of  the  fine  dirt  and  stone  dust  washed  from  the  sur- 
face of  the  roadway.  The  fine  particles  of  dust  between  the  grains 
of  sand  act  mechanically  to  decrease  the  mobility  of  the  sand,  and 
also  increase  capillary  attraction  and  diminish  percolation,  which 
in  turn  also  keeps  the  sand  damp  and  still  further  decreases  its 
mobility.  Apparently,  then,  the  incorporation  of  fine  dust  in  a 
sand  road  would  improve  it;  but  it  would  be  difficult  to  procure 
sufficient  dust  for  this  purpose. 


CHAPTER  IV. 
GRAVEL   ROADS. 

230.  Gravel  may  be  defined  as  a  mass  of  small,  more  or  less 
rounded  fragments  of  stone  which  have  been  broken  out  and  shaped 
by  the  action  of  water  or  of  ice.  When  properly  applied  gravel 
makes  an  excellent  road  surface, — superior  to  ordinary  earth  but 
not  possessing  the  wearing  qualities  of  first-class  broken  stone. 
Gravel  has  an  advantage  over  artificially  broken  stone  that  the 
former  is  already  prepared  and  is  therefore  the  cheaper.  A  gravel 
surface  is  most  suitable  for  country  highways  not  having  exceed- 
ingly heavy  traffic,  for  unfrequented  streets  in  villages  and  small 
cities,  and  for  park  roads. 

Many  of  the  principles  of  construction  are  the  same  for  gravel 
roads  as  for  broken-stone  roads;  but  usually  the  latter  are  much 
more  elaborately  constructed  than  the  former,  and  therefore  the 
two  will  be  discussed  separately. 

Art.  1.     The  Gravel. 

231.  REQUISITES  FOR  ROAD  GRAVEL.  To  be  suitable  for 
road-building  purposes,  gravel  should  fulfill  the  following  conditions : 
1.  The  fragments  should  be  so  hard  and  tough  as  not  easily  to  be 
ground  into  dust  by  the  impact  of  wheels  and  hoofs.  2.  The 
pebbles  should  be  of  different  sizes,  each  in  the  proper  propor- 
tion. 3.  There  should  be  intermixed  with  the  coarser  particles 
some  material  which  will  cement  and  bind  the  whole  into  a  solid 
mass. 

232.  Durability.  From  the  nature  of  their  origin,  it  is  apparent 
that  gravel  may  differ  widely  in  the  nature  of  the  stones  composing 
it.  Not  only  do  different  gravels  differ  from  each  other,  but  any 
particular  gravel  may  be  composed  of  fragments  of  a  variety  of 

146 


ART.    1.]  THE    GRAVEL.  147 

rocks.  Having  been  transported  a  considerable  distance  by  water 
and  ice,  gravel  is  usually  fairly  durable,  since  the  softer  and  more 
friable  fragments  have  been  worn  away.  Although  gravel  is  not 
equal  to  the  best  crushed  stone  for  road  building,  in  many  parts  of 
the  country  the  rocky  fragments  transported  by  water  and  ice  are 
more  durable  than  any  of  the  native  rocks.* 

233.  Sizes.  If  the  pebbles  are  too  large,  the  road  will  not  be 
homogeneous,  and  the  large  stones  will  work  to  the  surface  under  the 
action  of  traffic  and  frost;  but,  on  the  other  hand,  if  the  pebbles 
are  too  small,  the  gravel  will  partake  too  much  of  the  character  of 
sand,  and  will  be  difficult  to  bind  properly.  The  best  results  are 
obtained  when  the  largest  pebbles  are  not  more  than  £  to  1  inch,  or 
at  most  1$  inches,  in  greatest  dimension.  With  stones  larger  than 
1  inch,  it  is  difficult  to  keep  the  surface  from  breaking  up  when  dry. 
Small  gravel  makes  a  pleasanter  road  and  one  that  is  easier  to  keep 
in  order.  If  stones  larger  than  1  \  or  2  inches  are  present,  they  may 
be  screened  out  and  used  in  the  foundation  (§  257). 

It  is  desirable  that  the  several  sizes  should  be  so  proportioned 
that  the  smaller  ones  are  just  sufficient  to  fill  the  interstices  between 
the  larger  ones,  since  then  less  binder  is  required.  The  binder  is 
usually  the  least  durable  ingredient,  and  hence  the  less  there  is  of  it 
the  better.  Gravel  can  often  be  improved  by  screening — either  to 
remove  an  undesirable  size  or  to  separate  it  into  several  sizes 
afterward  to  be  combined  in  new  proportions.  The  proper  pro- 
portion depends  upon  the  nature  of  the  gravel — whether  the  binding 
material  is  already  present  in  the  form  of  dust,  or  whether  some  of 
the  pebbles  must  be  crushed  to  produce  the  binder. 

234.  Binder.  The  most  important  requisite  for  good  road- 
building  gravel  is  that  it  snail  bind  or  pack  well.  If  it  does  not  pack 
well,  the  wheels  will  sink  into  the  gravel  and  increase  the  force  of 
traction,  and  the  rain  water  will  penetrate  the  road-bed  and  soften 
it.  To  bind  well,  the  several  fragments  should  be  in  c'ontact  with 
one  another  at  as  many  points  as  possible,  in  order  that  they  may 
be  firmly  supported,  and  that  friction  may  act  to  the  best  advantage 
to  resist  displacement.     To  secure  contact  at  every  point,  all  the 


*  For  a  discussion  of  the  merits  of  the  principal  stones  for  road-building  pur- 
poses, see  Art.  1,  Chapter  V. 


148  GRAVEL  ROADS.  [CHAP    IV. 

interstices  between  the  fragments  should  be  filled — those  between 
the  large  pebbles,  with  small  pebbles;  those  between  the  small 
pebbles,  with  sand  grains;  and,  finally,  those  between  the  sand 
grains,  with  some  finer  material,  called  a  binder.  The  binding 
material  must  be  very  finely  divided,  so  that  it  can  be  worked  into 
the  smallest  interstices;  and  for  this  reason,  it  is  the  least  durable 
part  of  the  gravel,  being  easily  washed  out  or  blown  away.  For 
the  best  results,  then,  the  sizes  of  the  coarser  particles  should  be  so 
adjusted  as  to  require  a  minimum  amount  of  binder. 

The  binding  material  may  consist  of  clay,  loam,  silica,  stone  dust, 
iron  oxide,  etc.,  or  some  ingredient  which  will  crush  under  traffic 
and  furnish  a  fine  dust. 

Clay  is  by  far  the  most  common  binding  material ;  but  the  only 
|  recommendations  for  it  are  (1)  that  it  is  easily  reduced  to  an  im- 
palpable powder  by  the  action  of  wheels  or  by  water,  and  (2)  that 
it  is  often  found  already  mixed  with  the  gravel,  and  (3)  that  if  it 
-must  be  artificially  mixed,  it  is  plentiful  and  cheap.  Clay  is  an  un- 
desirable binder,  since  its  binding  action  depends  in  a  large  measure 
upon  the  state  of  the  weather.  During  a  rainy  period  it  absorbs  water 
and  loses  its  binding  power,  and  the  road  becomes  soft  and  muddy; 
while  in  dry  weather  it  contracts  and  cracks,  thus  releasing  the 
pebbles  and  giving  a  loose  surface.  Clay  is  also  very  susceptible 
to  the  action  of  frost;  and  consequently  when  the  frost  is  going  out, 
a  gravel  road  with  a  clay  binder  ruts  up  badly  and  frequently  breaks 
entirely  through.  When  the  weather  is  neither  too  damp  nor  too 
dry,  a  gravel  road  with  clay  binder  is  very  satisfactory.  The  clay 
should  be  no  more  than  enough  to  fill  the  voids  in  the  pebbles  and 
sand,  and  for  a  good  road-gravel  should  not  exceed  15  to  20  per  cent 
of  the  mass.  Not  infrequently  much  greater  quantities  of  clay  are 
present.  This  surplus  may  sometimes  be  removed  by  screening;  % 
but  often  it  can  be  removed  only  by  washing — a  process  which  is 
usually  so  expensive  as  to  be  prohibitive. 

Loam  is  chiefly  clay  mixed  with  sand  and  a  little  vegetable 
matter,  lime,  etc.;  and  as  a  binding  material  has  all  the  charac- 
teristics of  clay. 

A  very  finely  divided  silica,  easily  mistaken  for  clay,  is  occa- 
sionally present  in  gravel,  and  makes  an  excellent  binding  material. 

Iron  oxide  is  frequently  found  as  a  coating  on  the  pebbles  in 


ART.   1.]  THE    GRAVEL.  149 

such  quantities  as  to  cement  them  firmly  together.  These  ferru- 
ginous gravels  when  broken  up  and  put  upon  a  road,  will  again 
unite — often  more  firmly  than  originally,  because  of  the  greater 
pressure — and  form  a  smooth  hard  surface,  impervious  to  water. 
They  are  much  used  in  road  building,  gravel  from  Shark  River, 
N.  J., — much  used  around  New  York  City — and  that  from  the  Ohio 
river  near  Paducah,  Ky., — largely  used  in  the  neighboring  states — 
being  examples. 

235.  Comparatively  coarse  gravel  frequently  contains  some  in- 
gredients, as,  for  example,  fragments  of  limestone  or  shale,  which 
under  the  action  of  traffic  and  the  weather  reduce  to  a  powder  and 
form  a  good  binding  material.  Sometimes  gravel  contains  bits  of 
ironstone  (clay  cemented  with  iron  oxide)  in  the  form  of  thin  flat 
chips  which  break  and  crush  easily  under  the  wheels,  and  if  present 
in  any  quantity  make  a  most  excellent  binding  material. 

236.  The  binding  action  referred  to  in  the  preceding  discussion 
is  mechanical;  and  we  come  now  to  the  consideration  of  an  action 
not  yet  well  understood,  but  which  for  the  present  at  least  will  be 
called  chemical  action.  Experiments  seem  to  prove  that  if  fine 
powder  of  certain  stones  is  wetted  with  water  and  subjected  to 
compression,  a  true  chemical  cementation  takes  place.  Conse- 
quently some  stone  when  broken  into  small  fragments,  wetted  and 
traversed  by  heavy  wheels  or  by  a  road-roller  will  be  cemented 
together  to  a  considerable  degree.  This  cementation  is  due  to  the 
fact  that  the  friction  of  one  small  piece  of  stone  upon  another  pro- 
duces a  very  fine  powder  at  the  point  of  contact,  which,  when  wetted 
and  compressed,  forms  a  weak  cement.  Owing  to  the  rounded 
surfaces  of  water-worn  pebbles,  this  cementing  action  is  much  less 
with  gravel  than  with  rough  angular  fragments  of  broken  stone; 
but  with  gravel  composed  of  undecayed  rocky  fragments  this  action 
takes  place  to  a  considerable  degree.  As  a  rule,  pebbles  of  bluish 
color  will  thus  cement  together,  while  reddish  or  brown  ones  will 
not,  which  accounts  in  part  at  least  for  the  well  known  superiority 
of  blue  gravel  for  road  purposes.  Trap  rock  possesses  the  property 
of  cementation  in  a  high  degree,  and  hence  trap  gravel  is  a  very 
excellent  road-building  material.  Limestone  possesses  a  fair  de- 
gree of  cementation,  but  is  too  soft  to  wear  well.  Quartz  wears 
well  but  produces  little  or  no  dust  for  cementation,  and  besides  its 


150  GRAVEL  ROADS.  [CHAP.  IV. 

surfaces  are  so  smooth  and  hard  that  the  binder  has  but  little  effect ; 
and  therefore  it  rarely  happens  that  a  gravel  of  which  more  than 
one  half  of  its  bulk  is  white  quartz  pebbles  proves  to  be  a  good  road 
gravel. 

The  cementation  of  rocky  fragments  is  much  more  important  in 
a  crushed-stone  road  than  in  a  gravel  one,  and  therefore  the  subject 
will  be  more  fully  considered  in  Chapter  V. 

237.  The  binding  elements  heretofore  discussed  exist  naturally 
in  the  gravel;  but  gravels  are  often  found  that  do  not  contain  any 
binding  material,  and  in  such  cases  it  is  necessary  to  add  some 
cementing  material. 

Clay,  shale,  hard-pan,  marl,  loam,  etc.,  are  often  used  for  this 
purpose,  chiefly  because  they  are  so  plentiful  and  easily  applied; 
but  none  of  them  are  suitable  for  the  purpose,  as  they  all  have  the 
characteristics  of  a  clay  binder  (see  §  234).  With  any  of  them,  it 
is  difficult  to  keep  the  gravel  from  breaking  up — particularly  under 
heavy  traffic. 

In  some  localities  a  poor  iron  ore  is  found,  which,  when  mixed 
with  gravel,  makes  an  excellent  binder  and  gives  a  smooth  hard 
road  surface.  Bog  iron-ore,  which  occurs  in  marshes,  is  usually 
very  good  for  this  purpose. 

The  fine  dust  from  a  stone  crusher,  when  mixed  with  gravel,  will 
bind  it  together;  but  it  is  seldom  feasible  to  use  stone  dust  on  ac- 
count of  the  expense.  When  this  method  of  binding  gravel  is 
resorted  to,  the  construction  partakes  of  the  character  of  a  crushed- 
stone  road — a  subject  foreign  to  this  chapter.  The  chief  difference 
between  a  gravel  and  a  crushed-stone  road  is  in  the  thoroughness 
of  the  binding.  The  binding  of  a  gravel  Toad  is  due  chiefly,  and 
usually  solely,  to  the  mechanical  action  of  the  binder;  while  the 
binding  of  the  broken  stone  is  due  to  both  the  mechanical  and  the 
chemical  action  of  the  binder,  and  both  are  stronger  with  rough 
angular  fragments  of  broken  stone  than  with  water- worn  pebbles. 

238.  DISTRIBUTION  OF  GRAVEL.  The  gravel  beds  of  the 
glacial  drift  furnish  excellent  road-making  materials.  The  glacial 
ice  sheet,  often  a  mile  or  more  thick,  covered  New  England  and 
Canada  and  all  of  the  United  States  north  of  an  irregular  line  start- 
ing on  the  Atlantic  Coast  a  little  south  of  New  York  City  and  run- 
ning thence  successively  to  the  southwest  corner  of  the  State  of  New 


ART.    1.]  THE    GRAVEL.  151 

York,  to  Cincinnati,  to  a  point  a  little  north  of  the  mouth  of  the 
Ohio  river,  to  the  mouth  of  the  Missouri  river,  to  Topeka,  Kansas, 
thence  north  and  west  a  little  west  and  south  of  the  Missouri  river 
to  the  head  waters  of  that  stream,  and  thence  west  to  the  Pacific 
ocean.  All  of  the  area  north  of  the  above  described  line  was  cov- 
ered with  the  ice  sheet  except  small  portions  of  southeastern  Minne- 
sota, northeastern  Iowa,  northwestern  Illinois,  and  a  considerable 
portion  of  southwestern  Wisconsin.  As  this  ice  sheet  crept  to  the 
southward,  it  rent  great  quantities  of  stone  from  the  bed  rocks;  and 
these  materials  were  borne  southward,  either  in  the  slow-moving 
ice  or  hurried  along  by  the  violent  currents  of  water  which  swept 
forward  to  the  margin  of  the  ice  field.  Thus  impelled  the  under- 
ice  streams  were  able  to  bear  toward  the  margin  of  the  glacier  great 
quantities  of  stone.  The  original  range  of  the  glacial  gravels  has 
been  greatly  extended  here  and  there  by  the  streams,  which,  flowing 
southward  beyond  the  drift  belt,  have  often  carried  quantities  of 
the  hard  detritus  for  many  miles  beyond  the  limits  of  t^G  ice- 
field. 

Unfortunately  the  glacial  gravel  deposits  have  not  been  studied 
from  the  point  of  view  of  the  road-maker.  However,  it  is  known 
that  east  of  the  Hudson  river  the  glacial  supply  of  road  gravels  is 
only  here  and  there  of  economic  importance,  for  in  most  of  that  field 
the  glacial  waste  lies  on  native  rocks  which  are  suitable  for  road- 
making;  and  that  from  the  Hudson  to  the  Mississippi,  the  glacial 
deposits  of  bowlders  and  gravel  afford  better  road-building  mate- 
rials than  any  of  the  native  rocks.  Glacial  gravels  exist  in  consid- 
erable quantities  in  western  Pennsylvania,  in  the  greater  part  of 
Ohio,  in  northern  Itidiana,  and  in  northern  Illinois,  and  to  some 
extent  in  several  of  the  states  of  the  Northwest. 

239.  South  of  the  glacial  district,  the  rocks  exposed  to  the 
weather  have  decayed  by  a  process  of  leaching,  which  in  many  cases 
has  removed  strata  hundreds  of  feet  thick.  The  rocky  portion  is 
removed  in  proportion  to  its  solubility;  and,  as  a  result,  there  are 
often  left  concretions  of  cherty  matter  which  were  originally  con- 
tained in  beds  of  limestone.  This  cherty  residuum  of  flinty  mate- 
rial generally  lies  in  a  comparatively  thin  sheet  of  fragments  min- 
gled with  sand  and  clay;  but  occasionally  it  is  found  in  deposits 
from  which  the  clav  and  sand  have  been  removed  by  recent  or 


152  GRAVEL  ROADS.  [CHAP.  IV. 

ancient  streams,  leaving  the  material  well  suited  for  spreading  upon 
a  road.  Sometimes  this  cherty  residuum  is  found  in  layers  of 
fragments  many  feet  thick,  and  is  valuable  for  road-building  in  a 
locality  where  suitable  material  is  scarce.  The  presence  of  chert 
is  often  revealed  by  the  gullies  in  the  plowed  fields  and  along  the 
streams.  In  some  localities  very  good  roadways  are  constructed 
simply  by  shoveling  these  fragments  from  the  stream  beds  and 
depositing  them  on  the  road.* 

This  cherty  deposit  is  a  valuable  road  material  in  the  southern 
portion  of  the  Appalachian  mountains,  and  along  the  Ozark  foot- 
hills in  southern  Illinois  (particularly  in  Alexander  and  Union 
counties),  in  southern  Missouri,  and  in  northern  Arkansas.  Chert 
is  found  in  some  of  the  states  of  the  Northwest  where  the  glacial 
erosion  was  small,  so  that  the  rocks  that  had  decayed  before  the 
glacial  time  were  not  entirely  removed.  In  southwestern  Arkan- 
sas the  gravels  consist  of  fragments  of  novaculite  or  razor  stone — a 
material  of  nearly  the  same  geological  origin  and  physical  charac- 
teristics as  chert.  In  many  places  in  that  state  the  novaculite 
gravels  form  extensive  beds,  20  or  more  feet  thick.  At  the  southern 
extremity  of  the  Appalachian  mountain  system  is  a  wide-spread 
deposit  of  gravel,  termed  the  La  Fayette  formation,  whose  geologi- 
cal origin  is  not  determined.  This  deposit  often  attains  a  thickness 
of  40  to  50  feet,  and  is  a  valuable  source  of  road-building 
material. 

240.  If  gravel  be  defined  as  material  prepared  by  nature  ready 
to  be  laid  upon  the  road,  then  a  few  words  are  in  place  here  concern- 
ing iron  ore.  In  some  localities  there  are  low-grade  iron  ores 
which,  owing  to  the  admixture  of  various  impurities,  are  unfit  for 
use  in  making  iron,  that  may  be  valuable  for  road  building.  These 
low-grade  ores  are  widely  distributed;  and  generally  wherever 
limestone  occurs  below  a  considerable  thickness  of  sandstone,  the 
upper  portion  of  the  limy  layer  will  be  found  to  contain  iron,  and 
will  probably  make  a  fair  road  material.  A  lean  iron  ore  is  fre- 
quently found  in  marshes;  and  this  variety,  known  as  bog  ore, 
usually  makes  excellent  roads,  since  it  crushes  readily  and  gives  a 
smooth  hard  surface. 

*  For  a  discussion  of  chert  as  a  road-building  material,  see  §  295. 


ART.   1.]  THE    GRAVEL.  153 

241.  Exploring  for  Gravel.  In  searching  for  gravel  in  the 
glaciated  district,  the  following  suggestions  by  Professor  Shaler  * 
will  be  useful. 

"In  the  process  of  retreat  of  the  ice,  the  deposits  which  it  left 
were  accumulated  under  several  quite  diverse  conditions.  One  of 
these  produced  the  till,  or  commingled  coarse  and  fine  materials, 
which  had  been  churned  up  into  the  ice  during  the  time  of  its 
motion,  and  came  down,  when  the  melting  occurred,  as  a  broad, 
irregularly  disposed  sheet  which,  with  rare  exceptions,  is  to  be 
found  in  all  parts  of  the  glaciated  district,  save  where  it  has  been 
swept  away  by  streams. 

"Again,  from  time  to  time  during  the  closing  stages  of  the  ice 
age,  the  prevailingly  steadfast  retreat  of  the  ice  was  interrupted  by 
pauses  or  re-advances.  In  these  stages  there  was  formed  along  the 
margin  of  the  ice-field  what  is  called  a  frontal  moraine,  composed 
of  debris  shoved  forward  by  the  glacier  or  melted  out  of  it  along  its 
front.  These  moraines  are  in  most  cases  traceable,  where  they 
have  not  been  washed  away  or  buried  beneath  later  accumulations, 
in  the  form  of  a  ridge-like  heap  of  waste,  which,  as  we  readily  note, 
contains  much  less  clay  and  sand  and  therefore  a  larger  proportion 
of  gravel  and  bowlders,  than  the  sheet-like  deposit  of  till  above 
described.  In  some  cases  these  moraines  are  very  distinct  features 
in  the  landscape,  appearing,  from  the  number  of  large  bowlders 
which  they  expose,  much  like  ruined  walls  of  cyclopean  masonry. 
More  commonly  they  are  found  in  the  form  of  slight  ridges,  which 
may  be  covered  with  fine  material,  but  commonly  exhibit  here  and 
there  projecting  bowlders.  In  general  it  may  be  said  that  the 
moraines  afford  much  better  sites  for  pits  from  which  road  mate- 
rials are  to  be  obtained  than  the  till,  and  this  because  of  the  pre- 
vailing absence  of  clay  and  sand  in  the  deposits. 

"Here  and  there  in  almost  all  glaciated  districts,  especially  in 
the  valleys  of  the  greater  streams,  there  may  be  found  narrow  ridges, 
often  of  considerable  height,  and  almost  always  extending  in  the 
direction  of  the  ice  movement.  These  ridges  are  generally  termed 
by  geologists  eskars,  and  often  have  a  tolerable  continuity  for 


*  American  Highways,  N.  S.  Shaler,  Professor  of  Geology,  Harvard  University, 
p.  71-73. 


154  GRAVEL  ROADS.  [CHAP.  IV. 

scores  of  miles  at  right  angles  to  the  ice  front.  A  section  of  them 
shows  generally  a  gravelly  mass,  nearly  always  free  from  clay  and 
often  containing  little  sand,  though  occasionally  there  is  an  abun- 
dance of  large  bowlders,  which  have  a  prevailing  rounded  or  water- 
worn  form.  These  eskars  were  doubtless  formed  in  the  caves  be- 
neath the  ice  through  which  the  ancient  sub-glacial  streams  found 
their  way.  These  under-ice  rivers  were  much  given  to  changing 
their  position,  and  as  a  stream  lost  its  impetus  it  was  apt  to  fill  its 
ancient  arched-way  with  debris,  which  in  its  time  of  freest  flow 
would  have  been  sent  forward  to  the  ice  front.  At  many  places  in 
New  England  and  in  New  York  these  eskars  contain  large  and  use- 
ful deposits  of  gravel,  and  also  occasionally  quantities  of  bowlders 
well  fitted  for  crushing  as  regards  their  size  and  hardness.  In  the 
Western  States,  because  of  the  general  coating  of  deep  soil,  these 
eskars  are  less  easily  found;  but  they  exist  there,  and  should  be 
sought  for. 

"Where  the  eskars  terminate,  as  they  commonly  do,  on  a 
morainal  line,  there  is  almost  invariably  found,  immediately  in 
front  of  their  southern  terminations,  a  delta-like  deposit  which, 
though  generally  composed  in  large  measure  of.  sand,  frequently 
contains  near  the  moraine  extensive  accumulations  of  useful  gravel 
and  small  bowlders  which  are  fit  for  crushing. 

"Information  may  be  had  from  the  banks  of  streams,  where  by 
chance  they  have  cut  below  the  deep  coating  of  fine  materials.  The 
existence  of  any  distinct  uprise  of  the  surface  affords  some  reason 
to  expect  that  the  coarse  glacial  waste  may  be  at  that  point  not 
very  deeply  hidden.  It  is  probable  that  the  best  method  of  explora- 
tion is  by  any  simple  form  of  drill.  Even  the  ordinary  post-hole 
auger  may  be  made  to  serve  the  purpose." 

242.  Characteristics  of  Different  Gravels.  Any  gravel 

which  stands  vertical  in  the  bank,  showing  no  signs  of  slipping 
when  thawing  out  in  the  spring,  requiring  the  use  of  the  pick  to 
dislodge  it,  and  falling  in  large  chunks  or  solid  masses,  is  suffi- 
ciently clean  and  free  from  clay  for  use  on  the  road,  and  usually 
contains  just  enough  cementing  material  to  cause  it  to  pack  well. 

Pit  gravel  usually  contains  too  much  earthy  material,  and  can 
be  greatly  improved  by  screening.  Gravel  is  still  being  deposited 
in  drifts  and  bars  by  streams,  and  this  will  be  found  to  partake  oi 


ART.    1.]  THE    GRAVEL.  155 


the  character  of  the  pit  gravel  of  the  locality,  except  that  it  gen- 
erally contains  less  clay,  and  may  have  an  excess  of  sand.  This 
is  often  called  river  gravel,  and  is  one  of  the  best  sources  of  road 
material.  Lake  gravel  varies  greatly  in  character.  It  is  usually 
free  from  earth  and  contains  sufficient  sharp  sand  to  pack  well; 
but  is  liable  to  be  slaty — an  undesirable  quality. 

243.  Composition  of  Representative  Gravels.  In  an  endeavor 
to  determine  the  composition  necessary  for  a  road-building  gravel, 
samples  were  obtained  of  a  number  of  gravels  that  had  given  satis- 
factory service  in  the  road.  The  samples  in  each  case  were  selected 
by  a  person  thoroughly  conversant  with  the  use  of  that  particular 
material,  and  are  believed  to  be  fairly  representative. 

Table  17,  page  156,  shows  the  sieve  analysis  of  these  gravels. 
Each  sample  was  first  washed  in  successive  waters  until  the  water 
remained  clear,  and  then  the  wash  water  was  allowed  to  stand  until 
the  matter  in  suspension  was  precipitated.  The  precipitate  was 
dried  in  an  oven  to  dryness  and  then  weighed ;  and  the  washed 
gravel  was  air-dried,  and  then  sifted  and  weighed.  The  per  cent 
of  voids  in  the  washed  gravel  was  obtained  by  comparatively 
gently  ramming  the  gravel  under  water  in  a  small  metal  cylinder, 
the  ramming  not  being  severe  enough  to  crush  any  of  the  pebbles 
or  fragments. 

Table  18,  page  157,  shows  the  results  of  a  mineralogical  analysis 
of  such  of  these  gravels  as  had  passed  a  screen  having  £-inch  meshes. 
The  matter  recorded  in  Table  17  as  being  in  suspension  is  called 
clay  in  Table  18,  although  part  of  it  was  doubtless  organic  matter 
and  part  fine  sand,  but  the  error  is  not  material. 

244.  To  study  these  gravels  further,  each  will  be  considered  in 
order. 

1.  Urbana.  This  is  a  screened  drift  gravel  obtained  near  Ur- 
bana,  Champaign  Co.,  111.,  which  has  been  used  in  a  few  instances 
on  private  driveways.  Table  18  shows  only  3.8  per  cent  of  clay 
present,  which  will  have  only  a  small  binding  effect.  There  is 
7.6  per  cent  of  iron  oxide  (Fe2  Oa)  in  the  clay,  but  there  is  so  small 
a  proportion  of  clay  in  the  gravel  that  the  iron  contained  in  it  will 
have  an  inappreciable  binding  effect.  The  principal  source  of  binder 
is,  then,  the  65  per  cent  of  ferruginous  limestone.  Limestone  it- 
self when  pulverized  makes  an  excellent  binding  material,  and  a 


156 


GRAVEL    ROADS. 


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158  GRAVEL  ROADS.  [CHAP.  IV. 

small  part  of  the  limestone  is  in  the  form  of  flat  chips  that  may 
be  easily  crushed  under  the  wheels,  but  the  most  of  the  frag- 
ments are  rounded  and  not  easily  crushed  except  by  comparatively 
heavily  loaded  wheels.  There  is  only  a  small  per  cent  of  crys- 
talline rocks  present,  and  these  are  hard  and  not  readily  crushed, 
and  consequently  can  not  materially  affect  the  binding  qualities  of 
the  mass.  The  gravel  also  contains  22.2  per  cent  of  quartz;  but 
this  material  is  very  hard  and  not  easily  crushed,  and  besides  its 
dust  is  almost  wholly  devoid  of  cementing  properties.  Both  the 
quartz  and  the  crystalline  rocks  are  quite  sharp  and  angular,  which 
is  a  very  desirable  condition,  and  aids  the  binding  action  of  the 
clay  and  the  limestone  dust.  This  gravel  packs  only  slowly  in  the 
road,  particularly  under  the  light  traffic  of  a  private  driveway; 
but  under  moderate  traffic  makes  a  fairly  good  road,  and  is  not 
much  affected  by  freezing  and  thawing. 

2.  Decatur.  This  is  a  gravel  much  used  on  the  country  roads 
near  Decatur,  Macon  County,  111.,  with  satisfactory  results.  This 
gravel  has  a  comparatively  large  amount  of  fine  sand.  An  exam- 
ination of  Table  18  shows  that  it  contains  more  than  twice  as  much 
clay  as  the  Urbana  gravel,  but  only  about  one  third  enough  to 
fill  the  voids.  A  considerable  portion  of  the  limestone  both  of 
the  pure  and  the  ferruginous — a  total  of  30  per  cent, — is  in  thin 
friable  chips,  and  is  easily  crushed  by  the  traffic,  thus  making  an 
excellent  binder.  The  ferruginous  limestone  contains  an  unim- 
portant proportion  of  iron;  but  the  ferruginous  sandstone  is  heavily 
charged  with  iron  oxide,  which  makes  a  good  cementing  material. 
This  gravel  makes  a  smooth,  hard  surface,  reasonably  free  from 
dust  in  the  summer  and  mud  in  the  winter. 

3.  Lexington.  This  gravel  is  used  in  and  around  Lexington, 
McLean  County,  111.,  for  country  highways  with  entire  satisfac- 
tion. Notice  that  the  clay  is  equal  to  only  one  seventh  of  the 
voids.  Nearly  all  of  the  21  per  cent  of  ferruginous  limestone 
consists  of  thin  chips  which  are  easily  crushed  by  the  traffic.  Some 
binder  is  probably  obtained  from  the  58  per  cent  of  silicious  lime- 
stone. The  per  cent  of  crystalline  rocks  present  is  very  small,  and 
can  not  materially  affect  the  quality  of  the  gravel.  The  amount 
of  quartz  is  less  than  in  the  preceding  gravels,  and  is  an  unim- 
.portant  element. 


ABT.   1.]  THE   GRAVEL.  159 

4.  Rockford.  This  gravel  has  given  satisfactory  service  in  Rock- 
ford,  Winnebago  County,  111.,  probably  under  more  exacting  con- 
ditions than  any  of  the  preceding.  This  is  considerably  the 
coarsest  gravel  in  Table  17.  Notice  that  this  gravel  contains, 
roughly  speaking,  only  about  one  tenth  enough  clay  to  fill  the 
voids.  The  chief  source  of  binder  is  the  limestone  which  ex- 
ists in  the  form  of  pebbles,  but  contains  no  considerable  amount 
of  iron  or  silica.  The  basic  crystalline  rocks  by  decomposing  may 
furnish  a  little  binder;  but  as  they  are  round  hard  pebbles,  not 
easily  crushed,  the  binder  derived  from  this  source  can  be  of  no 
practical  importance.  A  very  little  cementing  material4  may  be 
derived  from  the  iron  conglomerate  and  also  from  the  limestone 
and  quartz  conglomerate. 

5.  Peekskill.  This  gravel  is  from  Roa  Hook,  a  " point"  in  the 
Hudson  river  near  Peekskill,  N.  Y.,  and  is  much  used  in  and 
around  New  York  City,  where  it  is  considered  one  of  the  best  road 
gravels.  Notice  that  the  clay  is  less  than  one  thirtieth  of  the  vol- 
ume of  the  voids.  Considerable  binding  material  is  doubtless 
derived  from  the  ferruginous  limestone,  which  contains  a  com- 
paratively small  per  cent  of  iron.  The  iron  in  the  ferruginous 
sandstone  is  too  small  in  amount  to  be  appreciable.  Some  binder 
is  doubtless  derived  from  the  metamorphosed  rocks  containing 
iron,  silica,  and  mica.  Notice  that  there  are  nearly  30  per  cent 
of  crystalline  rocks,  which  upon  being  finely  pulverized  will  fur- 
nish an  excellent  cementing  material,  particularly  after  being 
decomposed.  This  gravel  requires  considerable  rolling  with  a 
heavy  roller  to  crush  the  several  ingredients  and  liberal  sprinkling 
to  work  the  pulverized  material  into  the  voids,  before  the  mass 
binds.  All  the  other  gravels  bind  and  make  fair  roads  under  ordi- 
nary traffic. 

6.  Buck  Hill.  This  gravel  was  obtained  from  the  Buck  Hill  pit 
at  Tuckahoe,  N.  J.  It  was  recommended  as  a  representative 
gravel  by  Hon.  Henry  I.  Budd,  State  Commissioner  of  Public 
Roads  of  New  Jersey.  This  gravel  consists  practically  of  clay 
and  partially  rounded  quartz  pebbles.  The  metamorphosed 
rock  is  angular  and  friable.  The  clay  is  probably  enough  to  fill 
the  voids  when  the  gravel  has  been  compacted  by  traffic.  This 
is  the  first  of  the  samples  in  which  the  iron  contained  in  the  clay 


160  GRAVEL  ROADS.  [CHAP.  IV. 

is  appreciable,  and  the  iron  doubtless  has  an  important  part  in 
binding  the  road.  This  gravel  is  used  for  road  building  with- 
out rolling. 

7.  Rock  Hill.  This  sample  was  obtained  from  the  Rock  Hill 
pit  at  Tuckahoe,  N.  J.,  and  is  substantially  the  same  as  No.  6 
above,  except  in  having  a  greater  per  cent  of  voids  and  in  contain- 
ing some  sandstone  which  crushes  easily  and  materially  reduces 
the  voids  of  the  gravel  after  it  has  been  compacted  in  the  road. 
It  is  said  that  the  best  results  are  obtained  by  mixing  this  and 
the  preceding  gravel  half  and  half. 

8.  Shark  River.  This  gravel  was  obtained  from  the  Manasquan 
Gravel  Co.  of  Asbury  Park,  N.  J.,  and  is  much  used  in  Southern 
New  Jersey  and  around  New  York  City.  It  consists  wholly  of 
clay  and  small  rounded  pebbles  of  pure  white  quartz,  and  conse- 
quently the  only  binding  material  is  the  clay  and  the  2  per  cent 
of  iron  contained  in  it. 

9.  Oaktown.  This  is  a  gravel  obtained  from  the  Wabash  river, 
a  few  miles  above  Vincennes,  Ind.,  by  dredging,  which  has  been 
used  on  the  roads  entering  Oaktown,  Knox  Co.,  Ind.  There  is 
very  little  clay  in  this  gravel, — only  7.1  per  cent,  if  the  shale  be 
considered  as  clay,  as  it  is  practically.  The  chief  source  of  binding 
material  is  the  18.9  per  cent  of  carbonate  of  lime,  much  of  which 
is  in  the  form  of  flat  chips.  The  metamorphic  rocks  are  also  in 
thin  chips,  and  are  easily  pulverized.  The  crystalline  rocks  and 
the  quartz  are  comparatively  rough  and  angular.  In  service  the 
limestone  pebbles  grind  up  under  traffic,  and  the  road  becomes 
hard  and  firm,  and  is  not  much  affected  by  freezing  and  thawing. 

10.  Shaker  Prairie.  This  gravel  is  found  in  a  pit  on  Shaker 
Prairie,  west  of  Oaktown,  Knox  Co.,  Ind.,  and  consolidates  under 
traffic  much  more  quickly  than  the  preceding,  the  two  being  used 
side  by  side.  This  gravel  contains  only  a  comparatively  small 
amount  of  fine  sand,  being  in  this  respect  about  on  a  par  with  the 
Peekskill  gravel — see  No.  5.  Table  17.  It  contains  a  compara- 
tively large  amount  of  clay,  being  in  this  respect  similar  to  the 
New  Jersey  gravels — No.  7,  8,  and  9  in  Table  17  and  18.  This 
gravel  has  more  iron  in  the  clay  than  any  of  the  samples  except 
the  Tuckahoe  gravels — No.  6  and  7.  The  limestone  is  in  compara- 
tively  large  rounded   pebbles,   and  not  specially  easily   crushed 


AKT.   1.]  THE    GKAVEL.  161 

under  traffic.     The  road  is  bound  almost  wholly  by  the   clay  and 
the  iron  in  it  and  by  the  pulverized  limestone. 

11.  Paducah.  This  gravel  came  from  a  pit  about  two  miles  west 
of  Paducah,  Ky.,  on  the  Ohio  river  at  the  mouth  of  the  Tennessee 
river.  It  makes  excellent  roads  that  pack  quickly  under  traffic 
and  are  not  much  affected  by  freezing  and  thawing.  The  coarse 
material  consists  of  water- worn  chert  pebbles,  and  is  cemented 
by  ferruginous  clay.  The  chert  is  brittle  and  crushes  with  a  sharp 
splintery  fracture,  and  consolidates  readily  under  traffic,  the  sharp 
angular  fragments  giving  an  immobile  mass  and  offering  excellent 
surfaces  for  the  cementing  action  of  the  binder. 

12.  Rosetta.  This  gravel  comes  from  the  Rosetta  pit  at  Fort 
Gibson,  near  Vicksburg,  Miss.,  and  is  much  used  by  the  Illinois 
Central  Railroad  as  ballast.  It  is  here  included  under  the  belief 
that  it  will  also  make  good  wagon  roads.  The  quartz  pebbles  are 
quite  rough  and  angular,  and  in  the  pit  seem  to  be  quite  firmly: 
cemented  together  by  ferruginous  clay. 

245.  Conclusion.  From  the  preceding,  the  following  conclusions 
may  be  drawn.  1.  The  relation  between  the  proportion  of  voids 
and  the  per  cent  of  clay  is  no  indication  of  the  road-building  qual- 
ities of  a  gravel,  for  under  traffic  some  of  the  fragments  may  crush 
and  decrease  the  per  cent  of  voids  and  at  the  same  time  increase 
the  amount  of  the  binding  material.  2.  The  friability  of  the 
pebbles  has  a  greater  effect  upon  the  road-building  qualities  of  a 
gravel  than  the  per  cent  of  the  voids.  3.  The  binding  material 
may  be  clay,  or  clay  and  iron,  or  pulverized  limestone,  or  all  of 
these  combined.  The  less  clay  the  more  slowly  will  the  road  bind, 
but  the  less  it  will  be  affected  by  frost. 

A  study  similar  to  the  preceding  will  not  certainly  determine 
the  suitability  of  a  gravel  for  road  purposes,  but  it  will  throw  valu- 
able light  upon  its  probable  behavior  in  the  road.  The  only  sure 
way  to  determine  the  road-building  qualities  of  a  gravel  is  to  test 
it  by  actual  service,  for  much  depends  upon  the  friability  of  the 
pebbles,  the  weight  of  the  traffic,  the  climatic  conditions,  etc.  In 
applying  the  test  of  actual  service,  particularly  to  determine  the 
relative  merits  of  two  gravels,  account  should  be  taken  of  (1)  the 
nature  of  the  soil,  (2)  the  care  employed  in  preparing  the  founda- 
tion, (3)  the  quantity  of  material  used,  (4)  the  amount  of  traffic, 


162  GRAVEL  ROADS.  [CHAP.  IV. 

(5)  the  care  given  to  maintaining  the  road,  and  (6)  the  length  of  time 
the  material  has  been  in  service.  The  character  of  a  gravel  road 
is  generally  indicated  by  the  sound  of  the  metal  tires  of  the  wheels 
of  the  vehicles  passing  over  it.  If  the  wheel  makes  a  continuous 
crisp  gritty  sound,  the  road  is  reasonably  good;  if  the  gritty  sound 
is  absent,  there  is  probably  too  much  earthy  matter  on  the  sur- 
face; and  if  the  sound  is  intermittent  and  discontinuous,  there 
are  probably  too  many  large  pebbles  in  the  surface  material. 

Art.  2.     Construction. 

246.  The  subgrade  for  a  gravel  road  should  be  prepared  in  sub- 
stantially the  same  manner  as  an  earth  road  (see  Art.  1,  Chapter 
III).  Indeed  a  first-class  earth  road  is  the  best  foundation  for  a 
gravel  road. 

247.  DRAINAGE.  In  no  case  should  the  drainage  be  neglected 
— neither  the  side  ditches  nor  the  underdrainage.  With  the  hard, 
impervious  surface  of  a  gravel  road,  the  water  reaching  the  side 
ditches  is  greater  than  with  an  earth  surface;  and  therefore  the 
side  ditches  should  be  larger  for  gravel  and  broken-stone  roads  than 
for  earth  ones. 

A  gravel  road  upon  an  undrained  soil  entails  a  needless  expense 
for  maintenance,  and  is  never  so  good  as  if  the  road-bed  had  been 
thoroughly  underdrained.  Not  infrequently  a  thin  coating  of 
gravel  has  been  thrown  upon  an  undrained  foundation,  only  to 
sink  out  of  sight  in  a  year  or  two,  and  the  attempt  to  secure  a 
gravel  road  has  been  abandoned.  In  such  cases  a  comparatively 
small  expense  for  underdrainage  would  have  resulted  in  a  fair  road 
instead  of  a  failure.  The  total  amount  of  good  road-building  ma- 
terial in  the  world  is  small  in  comparison  with  the  possible  future 
demand,  and  therefore  it  is  a  public  misfortune  to  have  any  of  it 
wasted  in  bungling  attempts  at  road  building.  One  purpose  of 
the  gravel  is  to  give  a  more  or  less  rigid  layer  which  will  distribute 
the  concentrated  pressure  of  the  wheels  over  a  sufficiently  large 
area  of  the  earth  foundation  to  enable  it  to  support  the  load  with- 
out indentation.  The  thickness  of  gravel  required  to  support  the 
load  depends  upon  the  degree  of  the  drainage,  since  the  more  water 
in  the  earth  the  less  load  it  can  support.     Underdrainage  costs 


ART.  2.]  CONSTRUCTION.  163 

nothing  for  maintenance,  and  decreases  the  amount  of  gravel  re- 
quired, and  also  the  cost  of  maintaining  the  surface. 

248.  The  tile  should  be  placed  under  the  side  ditches — as  de- 
scribed for  earth  roads  (§  109).  Some  writers  recommend  that  a 
tile  be  laid  under  the  middle  of  the  gravel  or  broken  stone,  with 
the  earth  sloping  both  ways  to  the  tile.  There  are  several  objec- 
tions to  this  construction:  (1)  sloping  the  earth  is  not  of  much 
advantage,  and  (2)  it  needlessly  increases  the  depth  of  the  gravel 
or  broken  stone;  and  (3)  if  the  road  is  otherwise  Well  made,  the 
surface  should  be  practically  impervious  to  water.     See  §  109. 

Some  writers  advocate  a  tile  each  side  of  the  graveled  portion, 
with  short  lines  of  tile  running  each  way  from  the  center  of  the 
roadway  obliquely  to  the  side  tile,  these  "miter  drains"  to  be 
placed  15  feet  apart  in  wet  places.  Clearly  this  construction  is 
based  upon  a  misapprehension  of  the  source  of  the  water  reaching 
a  drain  tile.  The  water  that  enters  a  tile  comes  from  below  and 
not  directly  down  from  above.  It  is  abundantly  proven  that  in 
an  earth  road  needing  underdrainage,  little  or  no  water  penetrates 
the  surface;  and  with  good  gravel  or  broken  stone  roads  there  will 
be  still  less.  Therefore  "  miter  underdrains  "  below  the  graveled 
portion  of  the  roadway  are  absolutely  worthless,  and  tiles  at  the 
edges  of  the  hardened  way  are  no  better  than  tiles  under  the  side 
ditches. 

249.  CROWN.  The  same  general  principles  concerning  the 
crown  apply  in  gravel  roads  as  in  earth  roads — see  §  115-16.  The 
slope  of  the  gravel  surface  from  the  center  to  the  side  should  be 
at  least  one  quarter  of  an  inch  per  foot,  and  it  should  not  be  more 
than  three  quarters  of  an  inch  per  foot.  The  first  is  about  right 
for  park  drives,  which  have  light  traffic  and  are  well  cared  for;  if 
the  drive  is  narrow,  the  crown  may  be  a  little  greater  than  this; 
but  if  it  is  broad,  the  crown  should  be  less,  to  prevent  the  surface 
from  being  gullied  out  near  the  gutters  by  the  water  running  from 
the  center  to  the  sides.  The  maximum  crown,  as  above,  would  be 
about  right  for  a  country  gravel  road  with  heavy  traffic,  or  for  a 
street.  If  the  gravel  contains  an  excess  of  clay,  the  crown  should 
be  greater  than  the  above  maximum,  as  the  surface  will  be  liable 
to  rut  up. 

Frequently  gravel  roads  have  an  excessive  crown,  which  forces 


164  GRAVEL  ROADS.  [CHAP.  IV. 

traffic  to  use  a  narrow  strip  in  the  center — see  §  114.  This  results 
from  the  fact  that  the  gravel  is  placed  thicker  at  the  center  than 
at  the  edges,  upon  an  earth  road  which  already  has  some  crown; 
and  thus  the  surface  of  the  gravel  is  given  a  greater  crown  than 
the  original  earth  road,  while  a  gravel  road  should  have  a  less 
crown  than  an  earth  one. 

For  a  discussion  of  the  mathematical  form  of  the  transverse 
profile,  see  §  309-12. 

250.  FORMS  OF  CONSTRUCTION.  There  are  two  forms  of  con- 
struction of  country  gravel  roads,  which  differ  as  to  the  manner 
of  preparing  the  subgrade  to  receive  the  gravel.  In  one  form  the 
gravel  is  simply  deposited  on  the  surface  in  a  strip  along  the  middle 
of  the  former  earth  road;  and  in  the  other  a  trench  is  excavated 
in  which  the  gravel  is  placed.  For  convenience  of  reference  the 
former  will  be  called  Surface  Construction,  and  the  latter  Trench 
Construction. 

251.  Surface  Construction.  The  crudest  form  of  this  method 
of  construction  consists  in  dumping  gravel,  as  it  comes  from  the 
bank,  in  piles  in  line  on  an  earth  road.  The  quantity  of  gravel  is 
gaged  by  dumping  a  load  in  one,  or  two,  or  three  lengths  of  the 
wagon.  Little  or  no  attention  is  given  to  leveling  off  the  top  of 
the  piles,  and  it  is  not  rolled  except  as  traffic  is  forced  upon  the 
ridge  when  the  earth  upon  the  sides  gets  muddy.  For  the  first  year 
or  two  after  construction,  such  a  gravel  road  is  little  if  any  better 
than  an  earth  one.  The  surface  is  full  of  cradle  holes  and  is  easily 
cut  into  ruts;  and  the  loose  material  absorbs  the  rain,  and  be- 
comes mixed  with  the  soil  below.  If  the  gravel  is  good,  the  road 
becomes  fairly  good  after  the  gravel  has  been  packed  by  travel  and 
after  the  holes  have  been  filled  up  by  the  addition  of  new  material. 
This  form  of  construction  is  common  where  gravel  is  plentiful  the 
work  usually  being  done  by  labor  road-tax. 

252.  Another  form  of  surface  construction  consists  in  setting 
up  two  lines  of  plank  on  edge  and  filling  the  space  between  them 
with  gravel.  The  gage  planks  are  set  on  edge,  8,  10,  or  12  feet 
apart  according  to  the  importance  of  the  road,  and  the  gravel  is 
rilled  in  between  the  planks,  8  or  10  inches  deep  at  the  sides  and 
12  or  15  at  the  center.  Of  course,  when  the  boards  are  moved 
forward  to  be  used  again,  the  edge  of  the  gravel  spreads  out  and 


ART.  2.]  CONSTRUCTION.  165 

takes  the  natural  slope,  and  under  traffic  it  spreads  out  still  further. 
Ordinarily  in  this  form  of  construction  the  gravel  is  not  rolled, 
and  there  is  little  or  no  driving  over  it  by  teams  engaged  in  the 
construction.  The  only  advantage  of  this  method  over  the  pre- 
ceding one  is  that  it  affords  a  means  of  gaging  the  depth  of  gravel 
and  of  determining  the  quantity  used;  and  the  chief  objection  to 
it  is  that  when  gravel  is  put  on  in  a  thick  layer,  the  lower  part  is 
not  consolidated  well,  at  least  not  for  a  considerable  time,  and 
therefore  the  surface  is  liable  to  break  up.  This  form  of  construc- 
tion is  very  common. 

253.  In  the  best  form  of  surface  construction,  the  former  earth 
road  is  first  smoothed  up  with  the  scraping  grader, — if  necessary, 
reducing  the  crown.  If  after  smoothing  the  surface  with  the 
grader,  the  foundation  is  not  already  firm  and  solid,  it  should  be 
rolled.  Next  a  layer  of  gravel  4,  or  at  most  6,  inches  deep  is  spread 
upon  the  prepared  subgrade,  and  leveled — either  by  hand  with  a 
shovel  and  rake,  or  with  a  harrow  or  scraping  grader.  In  dump- 
ing from  a  wagon  or  cart,  the  larger  stones  will  roll  to  the  outer 
edge  of  the  heap,  and  in  leveling  the  gravel,  care  should  be  taken 
that  these  are  scattered  and  covered  deeply  with  fine  material, 
for  otherwise  the  road  will  not  have  an  uniform  texture  and  will 
wear  unevenly,  and  the  large  stones  are  liable  to  work  to  the  top. 

If  the  teams  hauling  the  gravel  are  required  to  drive  over  that 
already  placed,  the  road  will  be  consolidated  much  sooner;  but 
as  the  tractive  resistance  on  loose  gravel  is  very  great,  there  is 
some  disadvantage  in  this  requirement.  If  it  is  to  be  insisted 
upon,  the  construction  of  the  road  should  begin  at  the  end  nearest 
the  gravel.  The  gravel  can  be  consolidated  with  a  roller,  but  not 
as  effectively  as  by  traffic,  since  no  roller  gives  so  great  a  pressure 
as  the  wheels  of  loaded  wagons.*  Heavy  loads  should  not  be 
permitted  to  go  over  the  road  while  the  surface  is  soft,  for  fear  the 
wheels  will  cut  through  and  mix  the  earth  and  the  gravel.  While 
the  gravel  is  being  consolidated  by  the  passage  of  the  teams  em- 
ployed in  the  construction  or  by  ordinary  traffic,  all  ruts  should 
be  filled  as  soon  as  formed,  by  the  use  of  a  garden  rake,  and  all 
holes  should  be  filled  by  shoveling  in  fresh  gravel.     The  cost  of 

*  For  a  discussion  of  the  use  of  a  roller  on  gravel,  see  last  paragraph  of  §  254. 


166  GRAVEL  ROADS.  [CHAP.  IV. 

filling  depressions  and  ruts  will  be  more  than  saved  in   future 
repairs,  while  a  much  better  road  will  be  the  result. 

After  one  layer  has  been  thoroughly  consolidated  add  a  second, 
and  so  on  until  the  desired  depth  is  reached.  The  first  layer  may 
be  the  poorer  gravel,  the  best  being  reserved  for  the  top.  All  the 
layers  should  be  added  in  time  to  get  well  packed  before  the  rains 
and  frosts  of  winter  soften  the  road-bed. 

When  finished  the  gravel  should  be  deepest  at  the  center  and 
taper  off  to  the  sides.  It  is  immaterial  whether  the  first  layer  is 
the  widest  or  the  narrowest;  there  is  a  little  advantage  either  way. 
The  depth  necessary  will  depend  upon  the  nature  of  the  soil,  the 
quality  of  the  gravel,  the  amount  of  traffic,  the  maximum  weight 
per  wheel,  and  the  care  given  to  maintenance;  but  under  ordinary 
conditions,  a  depth  of  8  or  10  inches  of  compacted  gravel  at  the 
center  is  sufficient.  The  width  should  vary  with  the  amount  of 
traffic;  but  for  a  country  road  a  depth  of  6  inches  at  4  or  5  feet 
from  the  center  is  sufficient.  For  data  on  the  width  of  the  actually 
traveled  way  on  gravel  and  crushed-stone  roads,  see  §  306. 

254.  Trench  Construction.  In  this  form  of  construction,  a 
trench  is  excavated,  10  or  12  inches  deep  and  of  the  required  width 
(see  §  306),  for  the  reception  of  the  gravel.  The  bottom  of  the 
trench  is  usually  made  parallel  to  the  finished  road  surface  by 
sloping  it  from  the  center  toward  the  sides  (see  §  304).  Fig.  41 
shows  the  form  when  the  finished  surface  is  an  arc.  Fig.  41  is  the 
standard  form  for  state-aid  roads  in  Connecticut,  except  that  the 
width  of  the  graveled  way  may  be  12,  14,  or  16  feet.  The  crown 
is  £  inch  per  foot  of  distance  from  side  to  center,  or  6  inches  for  a 
16-foot  roadway.  There  is  not  much  difference  whether  the  road 
surface  is  an  arc  or  two  planes  meeting  in  the  center.  The  latter 
is  probably  a  little  the  better  for  country  roads,  although  the 
former  is  the  more  common.  Notice  that  in  Fig.  41  the  intersec- 
tion of  tlxe  road  surface  with  the  side  slope  of  the  embankment,  is 
rounded  off  somewhat  as  recommended  in  Fig.  13  and  14,  page 
89.  The  exact  method  of  rounding  off  the  corners  in  Fig.  41  is 
not  specified.  The  thickness  of  the  layers  as  shown  is  after  con- 
solidation. 

The  bottom  of  the  trench  should  be  rolled  to  consolidate  it  and 


ART.  2.]  COXSTRUCTIOX.  167 

to  discover  any  soft  places  in  the  foundation.  After  rolling,  any 
depressions  should  be  filled  and  then  re-rolled.  The  steam  roller 
is  better  for  this  purpose  than  the  horse  roller,  since  it  is  heavier 
and  since  the  horses'  feet  do  not  dig  up  the  subgrade.  For  a  dis- 
cussion of  rollers,  see  §  336-40.  For  precautions  to  be  taken  in 
rolling  the  subgrade,  see  §  326. 

A  layer  of  3  or  4,  or  at  most  6,  inches  of  gravel  is  placed  in  the 
trench,  and  the  gravel  is  consolidated  either  by  throwing  the  road 
open  to  traffic  or  by  rolling.  The  latter  is  preferable,  since  teams 
in  passing  each  other  are  liable  to  break  down  the  edges  of  the 
trench  and  mix  the  earth  with  the  gravel,  and  since  the  wheels  are 

i 

6ft. — -4* eft 

i 

rsr 


Gravp_ 


Hktttxftr  \     &in 

Half  Section  in  Cut  |       Half  Section  in  Fill 

i 

Fig.  41.— Connecticut  Gravel  Road. 

liable  to  break  through  the  thin  layer  of  gravel — particularly  if  a 
wet  time  intervenes.  If  the  only  gravel  available  contains  an 
excess  of  large  pebbles,  they  may  be  used  in  the  lower  layer,  in 
which  case  the  layer  can  not  be  compacted  either  by  the  wheels  or 
by  rolling.  If  the  gravel  is  only  slightly  deficient  in  binding  ma- 
terial, it  will  be  impossible  to  use  a  heavy  roller,  since  the  gravel 
will  push  along  in  front  of  it. 

Additional  layers  are  added  as  rapidly  as  the  preceding  one  is 
compacted,  until  the  desired  depth  is  reached.  Before  rolling  the 
last  layer,  the  earth  at  the  sides  of  the  trench,  i.  e.,  the  "  shoulders  " 
or  "'  wings,"  should  be  thoroughly  rolled;  and  then  the  rolling  of  the 
gravel  should  proceed  from  the  sides  toward  the  center,  to  prevent 
the  gravel  from  slipping  outward.  The  gravel  will  compact  much 
better  when  damp;  but  if  it  is  sprinkled,  care  should  be  taken  that 
(1)  the  gravel  is  not  made  so  wex  that  the  earthy  binding  material 
becomes  semi-fluid  and  collects  on  the  surface,  and  (2)  that  the 
subgrade  is  not  unduly  softened. 

No  practical  amount  of  rolling  will  cause  a  gravel  road  to  u  come 
down  "  in  the  sense  that  a  crushed-stone  road  does;  that  is,  a  gravel 


168  GRAVEL    ROADS.  [CHAP.   IV. 

road  can  not  be  rolled  until  the  surface  is  as  hard  as  it  will  probably 
be  after  it  has  been  opened  to  traffic  for  a  time,  since  even. the  heav- 
iest rollers  do  not  give  as  much  pressure  as  the  wheels  of  heavily 
loaded  wagons.  This  difference  between  gravel  and  broken-stone 
roads  is  due  to  the  fact  that  gravel  has  the  binding  material  origi- 
nally uniformly  distributed  throughout  the  mass,  while  with  broken 
stone  the  binder  is  spread  upon  the  top  and  worked  in  by  rolling 
and  sprinkling. 

255.  Surface  vs.  Trench  Construction.  Surface  construc- 
tion is  cheaper  and  seems  to  be  much  more  common  than 
trench  construction.  Surface  construction  is  the  better,  since  the 
depth  of  the  gravel  at  different  distances  from  the  center  is  approx- 
imately proportional  to  the  amount  of  traffic;  while  in  the  trench 
construction,  if  the  graveled  portion  is  wide  the  sides  are  liable 
not  to  be  much  used,  and  if  the  graveled  portion  is  narrow  passing 
vehicles  are  forced  upon  the  earth  shoulders.  Therefore  it  appears 
that  surface  construction  is  best  for  roads  having  a  large  amount 
of  traffic.  In  park  drives  and  streets,  the  whole  width  of  the  road- 
way is  excavated  and  filled  with  gravel. 

Trench  construction  is  a  little  more  economical  of  gravel,  and 
is  therefore  most  suitable  where  gravel  is  expensive. 

256.  Earth  Road  Beside  the  Graveled  Way.  It  is  sometimes 
advocated  that  there  should  be  two  tracks,  an  earth  road  for  sum- 
mer travel  and  a  graveled  way  for  winter  use.  This  plan  has  some 
advantages  and  also  some  disadvantages.  When  the  earth  track 
is  dry,  it  is  preferred  by  most  teamsters  to  the  hard  gravel  road; 
and  the  use  of  the  earth  roadway  decreases  the  wear  on  the  gravel, 
— which  is  clearly  an  advantage,  for  a  gravel  road  like  most  other 
things  will  wear  out.  On  the  other  hand,  if  the  summer  track 
is  immediately  adjacent  to  the  hardened  way,  the  earth  of  the 
former  will  become  mixed  with  the  gravel  of  the  latter,  much  to 
the  detriment  of  the  gravel.  The  chief  source  of  expense  in  the 
maintenance  of  gravel  roads  is  due  to  the  damage  done  by  the 
mixing  of  earth  from  the  side  of  the  road  with  the  gravel,  thus 
forming  a  mixture  that  will  hold  water  and  cause  the  road  to  cut 
up.  It  has  been  suggested  that  the  objection  to  the  two  tracks 
could  be  obviated  by  constructing  a  ditch,  or  sodding  a  narrow 
space  between  the  two;  but  this  is  impracticable.    The  two  tracks 


ART.  2.]  CONSTRUCTION.  169 

require  a  wider  right  of  way,  and  therefore  for  this  reason  are  fre- 
quently impossible. 

257.  BOTTOM  COURSE.  The  gravel  usually  contains  many 
stones  too  large  to  be  used  in  or  near  the  wearing  surface,  and 
therefore  it  is  economy  to  screen  the  material  and  lay  the  larger 
pebbles  in  the  bottom.  Some  writers  object  to  using  pebbles  larger 
than  1  or  1 J  inches  in  diameter  for  the  bottom  course,  on  the  ground 
that  the  heaving  effect  of  frost  and  the  vibration  due  to  the  pass- 
ing wheels  will  cause  the  larger  stones  to  rise  to  the  surface  and 
the  smaller  ones  to  descend — "  like  the  materials  in  a  shaken  sieve." 
Unquestionably,  if  a  vehicle  is  driven  over  a  layer  of  loose  stones 
of  all  sizes,  the  larger  ones  will  tilt  up  when  the  weight  comes  upon 
them  and  the  smaller  ones  will  roll  down  into  the  space  made  va- 
cant by  such  tipping;  and  by  a  repetition  of  this  process,  the  large 
stones  will  gradually  reach  the  surface.  The  heaving  action  of  the 
frost  acts  in  a  similar  way.  But  it  does  not  therefore  follow  that 
a  layer  of  coarse  stones  at  the  bottom  of  a  gravel  road  will  thus 
work  to  the  top  when  the  interstices  of  the  gravel  above  are  filled 
with  binding  material  and  all  is  compacted  by  traffic  or  by  rolling. 
Experience  has  shown  that  if  2  to  4  inches  of  the  top  dressing  has 
suitable  binding  material,  it  is  extremely  improbable  that  pebbles 
2  to  2J  inches  in  diameter  in  the  bottom  course  will  ever  work  to 
the  surface. 

258.  Other  materials  than  coarse  pebbles  may  be  used  for  the 
lower  course.  In  many  localities  there  are  large  quantities  of 
coal  slack,  which  is  useless  as  fuel  and  is  too  friable  for  the  wearing 
surface  of  a  road,  but  which  can  be  used  for  the  bottom  course  of 
a  gravel  road.  Coal  slack  has  thus  been  successfully  employed, 
and  is  often  cheaper  than  gravel.  Blast-furnace  slag  has  also  been 
used  for  this  purpose.  Sometimes  broken  stone  is  used  for  a  bot- 
tom course;  but  on  account  of  the  expense  of  breaking,  only  a 
stone  found  already  broken  in  the  quarry  is  suitable  for  this  pur- 
pose. A  "  flake "  stone  or  quarry  chips  are  the  forms  generally 
used.  The  celebrated  gravel  roads  of  Central  Park,  New  York 
City,  have  a  "  rubble  foundation  " — not  a  Telford  foundation  (§  302). 
The  rubble  layer  is  10  to  12  inches  thick,  and  the  gravel  4  to  6 
inches  after  being  thoroughly  compacted.  The  stones,  none  of 
which  exceeded  9  inches  in  greatest  dimensions,  were  dumped  upon 


170  GRAVEL    ROADS.  [CHAP.    IV. 

the  subgrade  from  carts  and  "evenly  adjusted  by  a  little  labor 
of  the  hand."  * 

259.  SCREENING  THE  GRAVEL.  As  a  rule  gravel  should  be 
screened  to  exclude  that  which  is  too  fine,  and  also  to  insure  an 
even  distribution  of  the  fine  and  coarse  material  when  placed  upon 
the  road.  Where  a  small  amount  of  gravel  is  required,  the  ordi- 
nary stationary  inclined  screen  is  used,  the  gravel  being  thrown 
against  it  with  a  shovel;  but  where  a  considerable  amount  is  re- 
quired, it  is  much  cheaper  to  use  a  rotary  screen  driven  by  power. 
For  the  best  results,  three  sizes  of  mesh  should  be  used — 2h  inch, 
1J  inch,  and  J  inch.  The  gravel  which  passes  the  first  is  to  be 
used  in  the  bottom;  that  which  passes  the  second,  in  the  middle 
course;  and  that  which  passes  the  third  is  used  on  top. 

If  the  gravel  contains  a  considerable  quantity  of  stones  more 
than  2\  inches  in  diameter,  a  stone  crusher  can  be  profitably  em- 
ployed, in  which  case  it  may  be  economical  to  use  an  elevator, 
rotary  screen,  and  elevated  storage  bins,  and  to  put  all  of  the 
gravel  through  the  crusher,  rotary  screen,  and  storage  bin  (see 
§  330). 

Under  favorable  circumstances,  the  cost  of  screening  by  hand 
will  be  about  15  cents  per  cubic  yard  for  each  time  the  material  is 
handled  with  a  shovel;  while  with  the  rotary  screen,  it  can  be 
screened  to  three  sizes  and  be  placed  in  elevated  bins  for  the  same 
amount. 

260.  If  the  gravel  must  be  put  through  the  crusher,  and  suitable 
stone  is  available,  a  broken-stone  road  may  be  more  economical 
than  a  gravel  one. 

261.  HAULING  THE  GRAVEL.  Gravel  is  usually  obtained  from 
pits,  and  is  generally  overlaid  with  more  or  less  earth,  which  should 
be  entirely  removed  before  beginning  to  haul  the  gravel.  Not 
infrequently,  this  earthy  material  is  allowed  to  tumble  into  the 
pit  and  mix  with  the  gravel,  greatly  to  the  detriment  of  the  fin- 
ished road. 

The  loading  of  the  gravel  can  be  greatly  facilitated  by  using  a 
board  platform  8  to  10  feet  long  and  4  to  6  feet  wide.     This  plat- 


*W.  H.  Grant,  Superintending  Engineer,  in  Fifth  Annual  (1862)  Report  of  the 
Board  of  Commissioners  of  Central  Park,  p.  67. 


ART.   2.]  CONSTRUCTION.  171 

form  is  placed  against  the  bottom  of  the  bank  in  such  a  manner 
that  when  the  gravel  above  is  dislodged  it  falls  upon  the  platform, 
from  which  it  is  easily  shoveled  into  the  wagon.  Often  the  plat- 
form can  be  supported  upon  legs  at  a  height  above  the  top  of  the 
wagon,  and  the  gravel  can  be  simply  pushed  off  into  the  wagon 
with  the  shovel.  Sometimes  the  circumstances  justify  the  use 
of  a  drag  scraper  (§  137) — drawn  by  a  horse  attached  to  a  cable  pass- 
ing through  a  block — to  drag  the  gravel  to  the  edge  of  the  plat- 
form, whence  it  drops  into  the  wagon;  and  sometimes,  if  a  large 
quantity  is  to  be  loaded  and  a  large  number  of  teams  are  engaged 
in  the  hauling,  the  wagons  can  be  loaded  with  a  trap — an  elevated 
platform  upon  which  the  gravel  is  hauled  with  a  drag  or  a  wheel 
scraper,  and  through  which  it  drops  into  the  wagon  below. 

262.  MEASURING  THE  GRAVEL.  When  gravel  roads  are  built 
by  public  officials,  the  gravel  is  usually  measured  in  place  in  the 
pit  or  in  the  wagon.  The  former  is  the  better  practice,  since  it  is 
more  definite.  When  the  road  is  built  by  contract,  the  gravel  is 
measured  (1)  in  the  wagons,  or  (2)  loose  in  the  road  by  means  of 
gage  boards,  or  (3)  compacted  in  the  road  by  means  of  established 
grades.  The  first  or  second  method  is  generally  used  with  surface 
construction,  and  the  third  with  trench  construction.  With  the 
last,  it  is  customary  to  require  that  the  finished  surface  shall  con- 
form to  an  established  grade,  and  consequently  a  considerable 
quantity  of  gravel  is  liable  to  be  forced  into  the  subgrade, — par- 
ticularly if  the  earth  foundation  is  made  to  conform  to  the  grade 
established  for  it.  The  specifications  for  state-aid  roads  in  New 
Jersey  specify  that  "  the  contractor  is  to  place  sufficient  gravel  on 
the  road  to  allow  it  to  shrink  33  per  cent  in  rolling  and  settling."  * 
Loose  gravel  with  clay  or  loam  binder  will  shrink  12  to  15  per  cent 
in  rolling,  and  gravel  in  which  the  binder  is  produced  by  crushing 
part  of  the  material  will  shrink  still  more — possibly  twice  as  much; 
the  above  specifications  provide,  therefore,  for  the  possibility  of 
forcing  18  to  21  per  cent  of  the  gravel  into  the  subgrade. 

If  it  is  expected  that  part  of  the  gravel  may  be  forced  into  the 
soil,  the  subgrade  may  be  left  a  little  higher  than  the  established 
grade,  and  then  the  addition  of  the  stipulated  amount  of  gravel  will 

♦Report  of  Commissioner  of  Public  Roads,  Trenton,  N.  J.,  1900,  p.  133. 


172  GRAVEL  ROADS.  [CHAP.  IV. 

bring  the  finished  surface  to  the  specified  grade.  Or,  a  thin  layer 
of  sand  on  the  subgrade  will  sometimes  prevent  the  gravel  from 
being  forced  into  the  soil.  For  a  further  discussion  of  this  subject, 
see  §  335. 

263.  COST.  The  cost  of  gravel  roads  varies  greatly  with  the 
form  of  construction,  the  cost  of  gravel,  the  amount  of  grading  and 
drainage  required,  the  width  and  thickness  of  the  gravel,  etc.  An 
average  depth  of  1  foot  over  a  width  of  13£  feet  requires  half  a 
cubic  yard  per  linear  foot  of  road,  or  2,640  cubic  yards  per  mile. 
The  gravel  usually  costs  from  5  to  10  cents  per  cubic  yard  in  the 
bank  stripped.  The  cost  of  loading  will  vary  from  5  to  10  cents  per 
cubic  yard,  not  including  the  time  lost  by  the  team  in  waiting  for 
a  load.  Setting  gage  plank,  leveling,  etc.,  may  cost  from  2  to  10 
cents  per  cubic  yard.  The  cost  of  hauling  varies  materially  with 
the  time  of  year  (see  §  4),  and  including  the  time  lost  in  load- 
ing and  unloading,  will  usually  be  at  least  15  cents  per  cubic  yard 
(about  1J  tons)  per  mile  and  seldom  more  than  30  cents — the 
former  when  done  by  farmers  in  the  slack  season  and  the  latter 
when  done  by  teamsters.  For  a  haul  of  1  mile  the  total  cost  in 
place  is  40  to  50  cents  per  cubic  yard. 

264.  Reports  from  forty-four  counties  in  Indiana  show  that  the 
total  cost  of  construction  of  gravel  roads  in  that  state  varies  from 
$800  to  $3,500  per  mile;  and  except  in  a  few  counties,  the  cost 
varies  from  $1,000  to  $2,500,  and  is  generally  from  $1,000  to  $2,000. 
The  cost  varies  with  the  distance  about  as  follows :  when  the  gravel 
is  hauled  1  mile,  the  total  cost  of  the  road  is  $1,000  per  mile;  when 
the  haul  is  2  miles,  $1,250  per  mile;  when  the  haul  is  3  miles,  $1,500 
per  mile;  when  the  haul  is  4  miles,  $1,750  per  mile;  and  if  5  miles, 
$2,000  per  mile.  Numerous  data  from  Ohio  and  Illinois  seem  to 
show  that  the  above  prices  are  fairly  representative. 

265.  Economic  Value  of  a  Gravel  Surface.  The  value 
to  a  community  of  covering  an  earth  road  with  gravel  is  a  subject 
the  discussion  of  which  leads  different  persons  to  widely  different 
conclusions,  these  depending  upon  the  point  of  view  and  upon  the 
data  assumed. 

The  advantage  of  a  gravel  surface  over  one  of  earth  is  that  the 
hard  and  impermeable  surface  of  the  former  is  equally  good  at  all 
seasons  of  the  year.     The  financial  value  of  a  road  which  is  good  at  all 


ART.  2.]  CONSTRUCTION.  173 

seasons  of  the  year  varies  greatly  with  the  locality  and  the  occupa- 
tion of  those  who  use  it.  Near  a  large  city  such  roads  are  nearly 
indispensable  to  dairymen,  fruit  growers,  and  truck  farmers;  but 
permanently  hard  roads  are  not  of  great  financial  advantage  to 
grain  growers  and  stock  raisers,  except  in  the  immediate  vicinity 
of  a  large  city.  A  road  which  is  uniformly  good  at  all  seasons  of 
the  year  is  of  some  economic  advantage  to  a  farming  community, 
since  it  permits  hauling  to  be  done  at  times  when  other  work  is 
impossible,  and  since  it  makes  possible  the  marketing  of  commodi- 
ties when  the  price  is  most  favorable.  It  is  impossible  to  compute 
the  money  value  of  these  factors;  but,  in  general,  it  is  not  very 
great  (see  §  4-7).  The  chief  advantage  of  a  road  good  at  all  seasons 
of  the  year  is  its  effect  upon  the  social  life  of  the  rural  district 

(8  1-3). 

The  amount  of  a  load  that  can  be  hauled  on  an  earth  road  is 
often  determined  by  the  grades  rather  than  by  the  nature  of  the 
surface;  and  unless  the  grades  are  light,  the  maximum  load  for  a 
gravel  road  is  not  much  greater  than  that  for  a  dry  earth  road. 
Therefore,  before  adding  a  gravel  surface  to  an  earth  road,  the 
gradients  should  be  carefully  studied  with  a  view  of  deriving  the 
utmost  benefit  of  the  improved  surface  by  securing  easy  ruling 
grades  (see  §  71). 

It  is  well  to  remember  that  under  certain  conditions  a  gravel 
road  is  neither  so  firm  nor  so  durable  as  a  first-class  crushed-stone 
road,  but  that  the  gravel  road  makes  an  excellent  foundation  for 
a  subsequent  surfacing  of  broken  stone. 

266.  The  cost  of  the  improvement  is  the  sum  of  (1)  the  annual 
interest  on  the  cost  of  construction,  (2)  the  excess  of  the  annual  cost 
of  maintaining  the  gravel  road  over  that  of  maintaining  the  earth 
road,  and  (3)  the  annual  payment  necessary  to  accumulate  a  fund 
sufficient  to  make  periodic  repairs,  i.  e.,  to  add  a  new  surface  at 
intervals.  The  money  spent  in  road  improvements  is  to  be  con- 
sidered as  an  investment  which  will  return  annual  interest  in  the 
reduced  cost  of  transportation  and  in  the  greater  freedom  of  traffic 
and  social  intercourse. 

267.  Gravel  vs.  Broken-stone  Roads.    With  the  utmost 

care  in  construction,  gravel  will  not  make  as  smooth  or  as  durable 
a  road  surface  as  first-class  broken  stone  on  account  of  the  impossi- 


174  GRAVEL  ROADS.  [CHAP.  IV. 


bility  of  binding  smooth  water-worn  pebbles  as  firmly  as  rough 
angular  pieces  of  broken  stone,  and  therefore  gravel  is  unsuitcd 
for  heavy  traffic  roads  or  streets,  often  being  for  these  less  econom- 
ical than  broken  stone,  owing  to  the  greater  expense  of  maintenance 
and  repairs.  On  account  of  the  low  first  cost  of  the  gravel,  and 
the  fact  that  reasonably  good  gravel  roads  can  be  built  without  any 
investment  of  money  in  rollers,  crushers,  and  other  costly  ma- 
chinery, they  are  well  suited  to  light  traffic  roads,  to  residence 
streets  in  small  cities,  and  to  park  drives.  Gravel  is  more  suitable 
for  park  drives  th#n  broken  stone  because  of  its  elasticity  and  its 
usually  darker  and  less  trying  color. 

Art.  3.     Maintenance. 

268.  Most  of  the  instructions  for  the  care  of  earth  roads — Art. 
2,  Chapter  III — apply  also  to  gravel  roads. 

269.  DESTRUCTIVE  AGENTS.  The  destructive  agents  are  the 
same  for  gravel  as  for  earth  roads  (see  §  187-93),  except  that  for 
gravel  roads  a  gradient  is  an  element  of  destruction  whose  impor- 
tance varies  with  its  steepness.  Horses  in  drawing  a  load  up  a  hill 
or  in  holding  back  a  load  in  coming  down,  are  liable  to  displace 
pebbles  with  the  calks  of  their  shoes,  and  after  the  first  stone  is 
displaced  it  is  easier  to  loosen  others.  The  locking  of  the  wheel, 
until  it  slides  in  going  down  hill,  is  also  hard  on  a  gravel  or  broken- 
stone  road. 

270.  WORK  OF  MAINTENANCE.  When  a  gravel  road  is  first 
thrown  open  to  traffic,  it  should  be  carefully  watched  and  all  incip- 
ient ruts  and  depressions  should  be  filled  as  soon  as  formed,  either 
by  raking  in  gravel  from  the  sides  of  the  depression  or  by  adding 
fresh  gravel — in  the  earlier  stages  of  this  work  the  former  is  the 
better,  and  in  the  later  stages  the  latter  is  necessary.  The  new 
gravel  should  be  finer  and  contain  more  binding  material  than 
that  employed  in  the  original  construction  of  the  road.  If  the 
depression  is  very  shallow,  it  is  wise  to  roughen  the  surface  with  a 
garden  rake  before  adding  the  new  material.  It  is  important  that 
even  ruts  and  shallow  holes  should  be  filled  as  soon  as  they  appear, 
for  they  will  hold  water,  which  will  soften  the  gravel  bed  and 
cause  the  road  to  wear  rapidly.     During  this  stage,  all  loose  stones 


ART.   2.]  MAINTENANCE.  175 

should  be  removed  from  the  roadway  both  for  the  comfort  of  trav- 
elers and  the  good  of  the  road.  At,  say,  every  |  mile  a  small  pile 
of  gravel  should  be  stored  to  be  used  in  filling  depressions. 

After  the  gravel  has  become  thoroughly  consolidated,  i.  e.,  after 
the  wheels  no-  longer  make  even  shallow  ruts,  the  only  care  the  road 
is  likely  to  need  for  several  years  is  to  keep  the  side  ditches  and 
culverts  free  from  weeds  and  floating  trash,  and  to  attend  to  the 
drainage  of  the  surface  when  the  snow  is  melting  (§  214). 

After  a  time  the  gravel  will  work  out  to  the  sides  of  the  road  too 
far,  and  the  center  will  wear  hollow.  It  will  then  be  necessary 
to  use  a  scraping  grader  (J  142-43)  to  push  the  gravel  back  to  the 
center.  In  doing  this  care  should  be  taken  not  to  scrape  up  the 
earth  with  the  gravel.  A  good  time  to  use  the  grader  is  just  after 
a  rain,  when  the  road  is  soft  and  easily  scraped,  and  when  the 
gravel  scraped  to  the  center  is  in  the  best  condition  to  pack  again. 
The  road  should  never  be  allowed  to  wear  so  hollow  in  the  center 
as  to  interfere  with  the  flow  of  water  from  the  surface  to  the  side 
ditches. 

271.  REPAIRS.  It  will  finally  be  necessary  to  repair  the  surface 
by  adding  a  coating  of  new  gravel.  For  this  purpose  the  size  of  the 
largest  pebbles  should  vary  with  the  thickness  of  the  coat.  It  is 
usual  to  put  the  gravel  on  by  making  two  or  three  dumps  of  a 
wagon  load,  i.  e.,  by  stretching  a  cubic  yard  over  15  to  25  feet, 
according  to  the  thickness  of  layer  required,  and  spreading  the 
gravel  just  a  little  wider  than  the  wagon  track.  Traffic  will  spread 
it  still  wider,  and  also  pack  it. 

In  making  repairs,  it  is  better  to  apply  a  thin  coat  often  than  a 
thicker  coat  less  frequently,  since  a  thick  coating  does  not  pack 
well.  A  layer  of  2  inches  of  gravel  is  better  than  more — unless 
on  a  spot  that  has  cut  through. 

272.  SPRINKLING.  A  gravel  road  with  clay  binder  needs  a 
little  moisture  to  hold  it  together,  since  the  clay  shrinks  and  cracks 
under  excessive  drought,  loses  its  binding  power,  and  permits  the 
road  to  break  to  pieces.  Under  such  circumstances  a  sprinkling 
with  water  is  a  means  of  preserving  the  road  from  serious  damage, 
although  on  account  of  the  expense  this  is  seldom  done  except  on 
park  drives. 

The  cost  of  sprinkling  the  drives  and  walks  in  Boston  parks  in 


176  GRAVEL  ROADS.  [CHAP.  IV. 

1891  was  2.4  cents  per  square  yard  per  annum,  of  which  one  quar- 
ter to  one  third  was  for  water  and  the  remainder  for  teaming  and 
labor.* 

273.  COST.  The  cost  of  maintenance  varies  with  the  climate, 
the  amount  and  nature  of  the  traffic,  the  quality  of  the  gravel,  etc. 
Data  from  Indiana  and  Ohio  show  that  it  varies  from  $40  to  $100 
per  mile  per  annum — the  former  where  the  traffic  is  light,  the 
gravel  good,  and  the  snow  light;  and  the  latter  where  the  traffic 
is  heavy,  the  gravel  poor,  and  the  snow  heavy. 

♦Journal  of  Associated  Engineering  Societies,  Vol.  11,  p.  441. 


CHAPTER  V. 
BROKEN-STONE  ROADS. 

274.  A  broken-stone  road  is  one  built  by  placing  small  fragments 
of  stone  on  the  ground  and  compacting  them  into  a  solid  mass. 
Such  a  road  is  frequently  called  a  macadam  road  after  John  Loudon 
MacAdam  (1756-1836),  a  famous  English  builder  of  broken-stone 
roads.  The  broken  stone  is  often  called  macadam,  and  the  work 
of  construction  macadamizing.  Small  fragments  of  broken  stone 
have  been  used  as  a  road  surface  from  time  immemorial,  and  a 
first-class  modern  broken-stone  road  differs  in  several  essentials 
from  the  form  advocated  by  MacAdam,  as  will  appear  later  in 
this  chapter  (see  §  302-04,  §  331,  and  §  336) ;  and  therefore  the  term 
macadam  is  not  altogether  appropriate  as  a  synonym  for  a  broken- 
stone  road.  Strictly  speaking  it  should  be  used  only  to  designate 
the  foundation  or  lower  course  of  a  stone  road  composed  entirely 
of  small  fragments  (§  302). 

A  broken-stone  road  is  sometimes  called  a  telford  road  after 
Thomas  Telford  (1757-1834),  a  famous  English  engineer;  but  the 
term  telford  is  usually,  and  appropriately,  restricted  to  a  partic- 
ular form  of  the  foundation  of  a  broken-stone  road  (see  §  302). 

Art.  1.    The  Stone. 

275.  REQUISITES  FOR  ROAD  STONE.  The  principal  requi- 
sites of  a  material  for  a  broken-stone  road  are  hardness,  tough- 
ness, cementing  or  binding  power,  and  resistance  to  the  weather. 
Usually  any  stone  that  is  hard  and  tough  will  resist  the  weather 
reasonably  well;  but  shales  and  slates,  though  hard  and  tough 
when  first  quarried,  often  disintegrate  when  exposed  to  the  weather. 
The  material  for  a  road  surface  should  also  be  uniform  in  quality 

177 


178  BKOKEN-STOXE  ROADS.  [CHAP.  V. 

or  the  surface  will  wear  unevenly,  and  the  depressions  which  occur 
where  the  material  is  comparatively  soft  will  hold  water,  thus 
softening  the  road-bed  and  occasioning  damage  difficult  to  repair. 

276.  Hardness  and  Toughness.  These  two  qualities  are  closely 
related.  Hardness  is  that  property  of  a  solid  which  renders  it 
difficult  to  displace  its  parts  among  themselves;  while  toughness 
enables  the  parts  to  yield  somewhat  without  being  separated  or 
broken.  For  road  purposes,  hardness  is  the  power  possessed  by 
a  rock  to  resist  the  rubbing  or  the  abrasive  action  of  wheels  and 
horses'  feet;  while  toughness  is  the  adhesion  between  particles 
of  a  rock  which  gives  it  power  to  resist  fracture  when  subjected  to 
the  blows  of  traffic.  A  stone  may  be  hard  and  brittle,  and  be 
quickly  pounded  to  pieces  in  the  road,  as  quartz;  or  it  may  have 
a  high  crushing  strength  and  yet  be  deficient  in  toughness,  and 
grind  away  speedily  under  the  abrasion  of  traffic,  as  some  varieties 
of  sandstones.  A  road  metal  should  have  enough  resistance  to 
crushing  to  support  the  load  brought  upon  it  by  the  wheels,  and 
enough  toughness  to  prevent  its  being  readily  ground  into  powder. 
A  large  part  of  the  fine  material  is  inevitably  swept  away  by  the 
rains  and  winds,  or  is  removed  by  scrapers  to  keep  the  road  in  good 
condition  during  wet  weather;  and  therefore  it  is  important  that 
the  fragments  should  be  tough  enough  not  to  be  unduly  pulverized 
by  the  traffic.  Toughness  is  incompatible  with  a  high  degree  of 
hardness,  and  in  a  measure  makes  up  for  a  deficiency  in  resistance 
to  crushing.  Hardness  could  be  measured  by  the  resistance  offered 
by  a  rock  to  the  grinding  of  an  emery  wheel;  and  toughness  would 
be  measured  by  the  resistance  to  fracture  when  struck  with  a 
hammer. 

277.  Cementing  or  Binding  Power.  Binding  power  is  the  prop- 
erty possessed  by  rock  dust  to  act  as  a  cement  between  the  coarser 
fragments  composing  a  stone  road.  This  property  is  of  the  highest 
value,  for  the  strength  of  the  binder  determines  the  resistance  of  the 
road  to  the  wear  and  tear  of  traffic  more  than  does  the  strength 
of  the  fragments  themselves.  It  is  possessed  in  a  very  much 
higher  degree  by  some  varieties  of  rocks  than  by  others,  and  its 
absence  is  so  pronounced  in  some  varieties  that  they  can  not  be 
made  to  compact  under  the  roller  or  under  traffic  without  the 
addition  of  some  cementing  agent.     This  subject  has  been  studied 


V 


ART.   1.]  THE    STOtfE.  179 

but  little,  and  only  by  the  Massachusetts  Highway  Commission, 
which  offers  the  following  tentative  conclusions:* 

"It  is  difficult  to  say  what  brings  about  this  cementation  or 
binding  of  rock  dust.  It  is  clear,  however,  that  with  many  va- 
rieties of  rock  it  is  due  to  several  causes.  Experiments  made  on  a 
number  of  different  kinds  of  rock  dust  showed  that  the  more  finely 
they  were  pulverized  the  higher  would  be  the  cementing  value  when 
subjected  to  pressure,  both  with  and  without  water;  and  an  increase 
in  pressure  seems  to  produce  a  corresponding  increase  in  cemen- 
tation. Further  than  this,  in  a  number  of  cases  similarly  made 
briquettes  of  the  same  rock  dust  gave  distinct  indication  that 
destruction  to  the  bond  of  cementation  by  impact  bore  a  definite 
relation  to  the  amount  of  energy  expended;  i.  e.,  about  the  same 
amount  of  energy  was  required  to  destroy  the  bond  in  each  briquette, 
even  when  applied  in  different  loads.  The  inference  drawn  from 
such  results  would  be  that  cementation  in  such  materials  is  to  a 
considerable  extent  mechanical, — that  is,  the  interlocking  of  the 
fine  particles  of  dust  caused  by  pressure. 

"  Another  important  fact  brought  out  was,  that  every  variety 
of  rock  experimented  on  gave  higher  cementing  results  when  com- 
pressed while  wet,  which  is  analogous  to  the  results  obtained  by 
road  builders,  who  almost  invariably  find  that  stone  screenings 
compact  better  when  watered  before  being  rolled.  This  at  first 
led  to  the  belief  that  this  result  was  entirely  due  to  a  chemical 
change  effected  by  the  water;  but  briquettes  made  of  pulverized 
glass,  mixed  with  pure  alcohol  instead  of  water,  gave  practically 
the  same  results.  The  only  explanation  of  this  fact  which  at  pres- 
ent suggests  itself  is  that  any  mobile  liquid  which  will  wet  the  fine 
particles  of  dust  acts  as  a  lubricant,  allowing  them  to  come  in 
close  contact  when  under  pressure. 

"  By  a  process  little  understood,  water  has  the  power  of  attract- 
ing the  fine  particles  of  rock  dust  and  cementing  them  together. 
This  is  well  illustrated  when  a  drop  of  water  falls  on  a  dry  hard 
road  surface  by  the  dust  immediately  buckling  into  an  irregular 
shape,  which  is  retained  until  destroyed  by  some  force.  On  exam- 
ining one  of  these  little  clods  after  drying,  it  will  be  seen  that  it 

♦Annual  Report  for  1900,  p.  71-2. 


180  BROKEN-STONE   ROADS.  [CHAP.  V. 

sensibly  coheres.  The  solidifying  of  mud  by  the  drying  up  of 
puddles  of  water  on  clayey  soil  is  another  example,  and  so  this 
same  process  can  be  traced  even  to  the  clay  concretions.  These 
phenomena  may  be  due  to  totally  different  causes;  nevertheless 
each  is  the  cementation  of  reck  dust,  brought  about  by  the  pres- 
ence of  water,  and  in  each  case  the  finer  the  dust  the  more  perfect 
this  action.  This  cementation  may  be  due  to  chemical  action, 
to  physical  re-arrangement  of  the  particles,  or  more  likely  to  a 
combination  of  such  causes." 

278.  Although  chemical  action  does  not  seem  to  affect  the  ce- 
menting power  of  stone  dust  as  determined  in  the  laboratory,  it 
is  probable  that  this  force  plays  an  important  part  in  the  road 
itself.  Many  native  rocks  consist  of  small  bits  bound  together 
by  a  cementing  material  which  was  deposited  from  the  water. 
Pure  water  will  dissolve  several  of  the  common  constituents  of 
rocks,  and  its  solvent  action  is  materially  increased  by  the  acids 
which  it  takes  up  from  the  atmosphere  and  from  manure  and 
decaying  vegetation  on  the  road  surface.  Water  percolating 
through  the  road  material  will  dissolve  lime,  silica,  and  iron, — 
common  cementing  materials  in  natural  rock, — and  later  deposits 
them  in  the  interstices  of  the  crushed  stone,  where  they  will  act  as 
a  binding  material.  This  binding  action  is  quite  slight,  but  may 
have  an  appreciable  effect  in  maintaining  the  delicate  adjustment 
of  a  broken-stone  road.  This  subject  has  not  been  investigated, 
but  it  is  apparently  worthy  of  careful  study. 

279.  METHOD  OF  TESTING  STONE.  There  are  two  methods 
of  determining  the  qualities  of  a  stone  for  road-building  purposes: 
(1)  by  using  the  stone  in  the  road  and  keeping  an  account  of  the 
cost  of  repairs  over  a  series  of  years,  or  (2)  by  laboratory  experi- 
ments. The  first  is  uncertain  owing  to  the  variations  in  climatic 
conditions,  and  in  the  amount  and  nature  of  the  traffic,  etc.,  and 
would  be  very  expensive  and  take  a  long  time.  In  the  second 
method  of  testing,  it  is  difficult  to  duplicate  in  the  laboratory  the 
conditions  of  actual  service;  but  nevertheless  much  valuable  in* 
formation  may  thus  be  obtained  at  a  moderate  expense  and  in  *» 
comparatively  short  time. 

The  first  method  of  testing  road-building  stones  will  be  consid- 
ered in  Art.  3 — Maintenance. 


ART.   1.]  THE    STONE.  181 

Systematic  laboratory  tests  of  road  metal  are  of  comparatively 
recent  origin,  and  may  be  said  to  have  been  started  by  the  French 
governmental  engineers  about  1880,  who  have  made  extensive 
use  of  this  method  in  determining  the  quality  of  the  rock  used 
in  contract  work  and  in  selecting  new  quarries.  Only  a  little  such 
laboratory  work  has  been  done  in  England  and  Germany.  From 
1894  to  1899  the  Massachusetts  Highway  Commission  conducted 
a  series  of  tests  of  road-making  materials,  and  developed  a  new 
and  important  method  of  testing,  and  deduced  much  valuable 
information. 

280.  Abrasion  Test.  This  test  determines  the  toughness  of  a 
stone,  and  is  employed  principally  by  the  French  engineers,  who 
use  the  machine  shown  in  Fig.  42.* 

"The  specimens  to  be  tested  are  sawed  into  rectangular  prisms 
having  a  4  cm.  (1.6  inches)  by  6  cm.  (2.4  inches)  base,  and  an  8  cm. 
(3.2  inches)  height.  These  specimens  are  placed,  two  at  a  time, 
so  that  they  rest  on  the  upper  surface  of  a  circular  grinding  disk 
of  cast  iron,  which  can  be  rotated  in  a  horizontal  plane  by  a  crank. 
They  are  held  in  clamps  so  arranged  that  the  bases  of  the  speci- 
mens rest  on  opposite  sides  of  the  grinding  surface,  26  cm.  (10.4 
inches)  from  the  center.  The  specimens  are  weighted  so  that 
they  press  against  the  grinding  disk  with  a  pressure  of  250  grammes 
(8.8  ounces)  per  square  centimeter  (0.4  inch).  Sand  is  fed  onto 
the  disk  from  a  funnel  above.  The  sand  used  is  of  a  standard 
quality  and  size,  obtained  by  crushing  quartzite  rock  and  screen- 
ing it  to  the  standard  size.  The  quantity  of  sand  used  in  each  test 
is  one  litre  per  specimen  for  each  thousand  turns  of  the  grinding 
disk.  The  disk  is  rotated  at  the  rate  of  1,000  revolutions  per  half 
hour,  and  a  test  is  completed  in  4,000  revolutions.  The  diminu- 
tion in  the  height  of  the  specimen  is  measured,  and  its  loss  in 
weight  determined  after  each  1,000  turns  of  the  disk.  The  per 
cent  of  loss  undergone  by  each  specimen  after  4,000  revolutions 
of  the  grinding  disk  is  set  down  as  the  result  of  the  test,  and  serves 
for  comparison."! 

281.  Impact  Test.  The  French  engineers  test  the  ability  of  a 
stone  to  resist  impact,  by  means  of  a  machine  which  resembles 

*  Report  of  Massachusetts  Highway  Commission  for  1900,  p.  76. 
\IUd. 


182 


BROKEN-STONE   EOADS. 


[CHAP. 


V. 


very  closely  in  principle  the  pile  driver.  The  hammer  is  raised  by 
a  cord  which  passes  over  a  pulley  at  the  top  of  the  guides  and  can 
be  released  at  any  desired  height,  from  which  it  falls  upon  the 
specimen,  which  is  held  below  by  clamps.  Two  hammers  are 
employed,  one  weighing  42  kilogrammes  (92.4  pounds)  and  the 
other  20  kilogrammes  (44  pounds),  their  respective  falls  being 
100  cm.   (40  inches)  and  80  cm.  (32  inches).     The   number   of 


Fig.  42.— Dorrey  Abrasion  Testing  Machine. 

blows  necessary  to  crack  the  specimen  and  also  the  number  to 
produce  its  complete  destruction  are  determined.  The  test  is 
made  upon  4-cm.  cubes,  at  least  three  cubes  being  used  for  each 
specimen  with  each  hammer. 

This  and  the  preceding  test  will  not  be  further  considered  here, 
since  the  resistance  to  impact  and  abrasion  are  more  easily  deter- 
mined by  the  method  immediately  following. 

282.  Abrasion  and  Impact  Test.  This  test  consists  in  placing 
a  known  weight  of  fragments  in  a  tight  drum  which  rotates  about 
an  eccentric  axis  so  that  the  bits  roll  over  one  another  and  also 


ART. 


i-] 


THE    STOXE. 


183 


shift  from  end  to  end  in  the  cylinder.  This  test  was  invented  by 
Deval,  a  French  engineer,  and  has  been  widely  used.  It  determines 
at  once  the  resistance  to  abrasion  and  also  to  impact,  and  is  an 
important  test  for  road  metal.  Fig.  43  shows  the  form  of  the 
Deval  machine  used  in  this  test  by  the  Massachusetts  Highway 
Commission.* 

"The  machine  consists  of  four  cylinders,  each  20  cm.  (7.9  inches) 
in  diameter  and  34  cm.  (13.4  inches)  in  depth.  Each  of  these 
cylinders  is  closed  at  one  end  and  has  a  tightly  fitting  cover  for 


Fig.  43.— Deval  Impact  and  Abrasion  Testing  Machine. 

the  other.  They  are  fastened  to  a  shaft  so  that  the  axis  of  each 
cylinder  is  at  an  angle  of  30°  with  the  axis  of  rotation  of  the  shaft. 
The  shaft  which  holds  the  cylinders  is  supported  by  bearings;  and 
at  one  of  its  ends  is  a  pulley  by  which  the  cylinders  are  revolved, 
and  at  the  other  a  revolution  counter. 

"The  stones  employed  in  making  the  abrasion  test  are  about 
the  size  used  in  making  macadam  roads — between  6.31  cm.  (2.5 
inches)  and  3.18  cm.  (1.25  inches)  in  diameter.  In  making  a  test 
5  kilogrammes  (11  pounds)  of  perfectly  clean  stone  of  the  above 
dimensions  are  placed  in  one  of  the  cylinders;  the  cover  is  then 
bolted  on,  and  the  cylinder  rotated  at  the  rate  of  2,000  revolu- 
tions per  hour  for  five  hours.  Four  tests  can  be  made  at  once, 
by  using  all  four  cylinders.  At  each  revolution  of  the  shaft  the 
fragments  of  stone  are  thrown  twice  from  one  end  of  the  cylinder 
to  the  other,  which  grinds  them  against  one  another  and  against 
the  walls  of  the  cylinder.  After  10,000  revolutions  the  machine 
is  stopped,  the  cylinder  opened,  and  the  contents  placed  on  a 
sieve  having  0.16  cm.  (TV  inch)  meshes.  The  material  that  passes 
through  the  sieve  is  put  aside  for  the  cementation  test.  The  sieve 
and  the  remaining  fragments  of  stone  are  then  held  under  running 

♦Annual  Report  for  1900,  p.  80. 


184  BROKEN-STONE   ROADS.  [CHAP.  Y. 

water  until  all  the  adhering  dust  is  washed  off.  After  these  re- 
maining fragments  have  thoroughly  dried  they  are  carefully 
weighed,  and  their  weight  is  subtracted  from  5  kilogrammes  (11 
pounds) — the  original  weight  of  all  the  stone  in  the  test.  The 
difference  obtained  is  the  weight  of  the  detritus  under  0.16  cm. 
(TV  inch)  worn  off  by  the  test." 

The  relative  resistance  of  stones  in  the  abrasion  test  is  expressed 
either  (1)  by  the  Per  Cent  of  Wear,  i.  e.,  by  the  ratio  of  the  weight 
of  the  dust  worn  off  to  the  original  weight  of  the  stone,  or  (2)  by 
the  Co-efficient  of  Wear  adopted  by  the  National  School  of  Roads 
and  Bridges  of  France.     The  latter  is  represented  by  the  formula: 

20      400 
Co-efficient  of  Wear  =  20  X  —  =  — , 

w        w 

in  which  iv  is  the  weight  in  grammes  of  detritus  under  0.16  cm. 
(TV  inch)  in  size  obtained  per  kilogramme  (2.2  pounds)  of  stone. 
The  French  road  engineers  usually  regard  a  co-efficient  of  20  as 
indicating  a  stone  excellent  for  road  purposes,  and  one  of  10  as 
sufficiently  good.  The  larger  the  Co-efficient  of  Wear  the  better  the 
stone;  while  a  small  Per  Cent  of  Wear  indicates  a  good  stone. 
The  Per  Cent  of  Wear  is  equal  to  forty  divided  by  the  Co-efficient 
of  Wear;  and  vice  versa,  the  latter  is  equal  to  forty  divided  by 
the  former. 

Table  19,  page  186,  gives  the  Per  Cent  of  Wear  obtained  by  the 
Massachusetts  Highway  Commission;  and  Table  20,  page  187, 
gives  similar  results  obtained  under  the  auspices  of  the  U.  S.  Agri- 
cultural Department — in  both  cases  under  the  direction  of  Mr. 
Logan  Waller  Page.  In  Table  20  the  Per  Cent  of  Wear  is  the  total 
percentage  of  all  material  less  than  1J  inches,  while  the  French 
Co-efficient  of  Wear  is  based  upon  the  percentage  of  material  less 
than  y1^  inch  in  diameter;  and  therefore  in  Table  20  these  results 
are  not  related  as  stated  in  the  preceding  paragraph. 

In  1901  the  U.  S.  Road  Material  Laboratory  introduced  a  new 
term  to  express  the  quality  of  a  road-building  material,  but 
called  it  Co-efficient  of  Wear.  In  Table  18  this  new  term  is  des- 
ignated Co-efficient  of  Wear  (U.  S.  A.  D.),  the  initials  in  the  paren- 
thesis standing  for  U.  S.  Agricultural  Department,  and  distin- 
guishes this  Co-efficient  from  the  similar  French  Co-efficient.     The 


ART.   l.J  THE   STOXE.  185 

U.  S.  A.  D.  Co-efficient  is  obtained  as  follows:  Subtract  4,000  from 
the  weight  of  the  abraded  material  larger  than  1 J  inches,  and  divide 
the  difference  by  10.  If  no  wear  takes  place,  the  Co-efficient  will 
be  100;  and  if  there  is  20  per  cent  of  detritus  smaller  than  1J 
inches,  the  Co-efficient  will  be  0,  and  the  material  is  considered 
unfit  for  road  making.  "This  term  was  introduced  to  secure  a 
result  with  more  range  to  it  and  one  that  could  be  more  easily 
understood  by  the  average  layman."  The  innovation  is  of  doubt- 
ful propriety. 

283.  Cementation  Test.  This  test  was  invented  by  Mr.  Logan 
Waller  Page,  Geologist  of  the  Massachusetts  Highway  Commis- 
sion, and  was  developed  during  the  years  1896  to  1899.  The  test 
is  made  by  wetting  the  stone  dust  with  water,  and  molding  it  into 
a  short  cylinder,  which  after  being  dried  is  subjected  to  the  blows 
of  a  dropping  weight. 

"To  make  the  test  specimen,  the  dust  of  rock  that  is  to  be 
tested  is  passed  through  a  screen  having  40  meshes  per  cm.  (100  per 
inch),  and  is  obtained  from  the  detritus  of  the  abrasion  and  im- 
pact test.  The  dust  is  made  into  briquettes  of  circular  sections, 
25  mm.  (0.98  inch)  in  diameter  and  25  mm.  in  height,  by  placing 
the  dust  in  a  metal  die  of  the  proper  dimensions,  with  enough  dis- 
tilled water  to  moisten  it  (4  cc.  or  0.24  cubic  inches) :  a  closely 
fitting  plug  is  then  inserted  on  top  of  the  wet  dust,  and  it  is  sub- 
jected to  a  pressure  of  100  kgs.  per  sq.  cm.  (1,422  pounds  per 
square  inch).  The  weight  of  the  dust  varies  with  the  density  and 
compressibility  of  the  stone,  but  generally  it  requires  about  25 
grs.  (0.9  ounce)  of  dust  to  make  a  briquette  of  the  above  dimen- 
sions. Two  weeks  should  be  allowed  for  a  briquette  to  dry,  at  the 
ordinary  temperature  of  a  room,  after  which  it  should  be  tested 
within  a  few  days. 

"  Fig.  44,  page  188,  shows  the  machine  employed  in  testing  the 
specimen.  The  machine  consists  of  a  1-kilogramme  (2.2-pound) 
hammer,  //,  arranged  like  the  hammer  of  a  pile-driver  on  two  ver- 
tical guides,  D.  The  hammer  is  raised  by  a  screw,  C,  and  dropped 
automatically  from  any  desired  height.  It  falls  on  a  flat-end 
plunger,  B,  weighing  1  kilogramme,  which  is  pressed  upon  the 
briquette,  0,  by  two  light  spiral  springs  held  by  the  guide  rods,  F. 
The  plunger,  B,  is  bolted  to  a  cross-head,  G,  which  is  guided  by 


186 


BROKEN-STOtfE   ROADS. 


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188 


BROKEN-STONE    ROADS. 


[CHAP.   V. 


SECTIONAL  PLAN  AA 


5i0c  elevation  trout  elewtjom 

Fig.  44.— Impact  Machine  for  Testing  Cementation. 


ART.   1.]  THE    STONE.  189 

two  vertical  rods,  F.  A  small  lever;  J,  carrying  a  brass  pencil, 
K,  at  its  free  end,  is  connected  to  the  side  of  the  cross-head  by  a 
link  motion,  arranged  so  that  it  gives  a  vertical  movement  to  the 
pencil  six  times  as  great  as  the' movement  of  the  cross-head.  The 
pencil  is  pressed  against  a  drum,  A,  and  its  movement  is  recorded 
on  a  slip  of  paper  fastened  thereon.  The  drum  is  moved  auto- 
matically through  a  small  angle  at  each  stroke  of  the  hammer; 
and  thus  a  record  is  obtained  of  the  movement  of  the  hammer  after 
each  blow.  The  standard  fall  of  the  hammer  for  a  test  is  1  cm. 
(0.39  inch),  and  the  blow  is  repeated  until  the  bond  of  cementa- 
tion of  the  material  is  destroyed.  The  final  blow  is  easily  ascer- 
tained, for  when  the  hammer  falls  on  the  plunger,  if  the  material 
beneath  it  can  withstand  the  blow,  the  plunger  re-bounds ;  if  not, 
the  plunger  stays  at  the  point  to  which  it  is  driven,  which  is  clearly 
recorded  on  the  slip  of  paper.  The  number  of  blows  required  to 
break  the  bond  of  cementation  is  taken  as  representing  the  binding 
power  of  the  stone."  * 

Table  19,  page  186,  shows  the  results  obtained  under  the  aus- 
pices of  the  Massachusetts  Highway  Commission;  and  Table  20, 
page  187,  gives  similar  results  obtained  in  the  Road-material  Lab- 
oratory of  the  U.  S.  Department  of  Agriculture — in  both  cases 
under  the  immediate  direction  of  Mr.  Page,  the  inventor  of  this 
method  of  testing  road  metal.  This  test  was  not  applied  to  as 
many  specimens  as  the  Impact  and  Abrasion  Test. 

284.  Crushing  Test.  This  test  in  a  degree  determines  the  hard- 
ness of  a  stone ;  but  it  is  seldom  applied  to  determine  the  suitability 
of  a  material  for  road  metal,  since  hardness  is  more  easily  deter- 
mined by  the  impact  and  abrasion  test  (§  283).  For  detailed 
instructions  as  to  the  method  of  making  the  crushing  test,  see  the 
author's  Treatise  on  Masonry  Construction. 

285.  Absorption  Test.  The  method  employed  by  the  Massachu- 
setts Highway  Commission  in  making  this  test  is  as  follows:  A 
smooth  stone,  between  20  and  60  grammes  in  weight,  that  has 
been  through  the  abrasion  and  impact  test  is  weighed  in  air.  It 
is  then  immersed  in  water,  and  immediately  re-weighed  in  the 
water.     Experiments   having   shown   that   absorption   practically 

*  Report  of  Massachusetts  Highway  Commission,  1900.  p.  80-8.1. 


IPO  BROKEN-CTOXE    EOADS.  [CHAP.  V. 

ceased  after  62  hours,  it  was  concluded  that  an  immersion  of  96 
hours  would  be  a  safe  allowance.  After  96  hours  of  immersion 
the  stone  is  again  weighed  in  water.  The  absorption  is  then  com- 
puted by  the  formula: 

G  —  B 
Number  of  pounds  of  water  absorbed  by  a  cubic  foot  of  rock  =      _    •  x  62.5, 

in  which  A  is  the  weight  in  air,  B  the  weight  immediately  after 
the  immersion  in  water,  C  the  weight  after  absorption  for  ninety- 
six  hours,  and  62.5  the  weight  of  a  cubic  foot  of  water. 

Table  19,  page  186,  shows  the  results  obtained  by  the  Massa- 
chusetts Highway  Commission,  and  Table  20,  page  187,  gives  similar 
results  by  the  U.  S.  Department  of  Agriculture. 

286.  The  absorptive  power  of  the  stone  is  tested  to  determine 
the  probable  effect  of  frost  upon  the  material.  It  is  well  known  that 
water  in  freezing  exerts  a  considerable  expansive  force;  but  this 
does  not  prove  that  freezing  will  seriously  injure  a  road  material 
that  absorbs  water  even  to  a  considerable  amount.  The  absorptive 
power  depends  upon  the  porosity,  and  when  a  porous  stone  is 
immersed  in  water  its  pores  are  filled  with  air,  which  the  water  does 
not  entirely  drive  out;  and  this  air  serves  as  a  cushion  to  take  up 
the  expansion  of  the  water  in  freezing.  For  this  reason,  freezing 
does  little  or  no  injury  to  stone  or  brick  which  are  otherwise  suitable 
for  road  purposes.  A  rock  or  brick  so  porous  as  to  be  damaged 
by  freezing  while  wet,  would  probably  be  rejected  by  a  casual 
inspection — certainly  by  the  tests  ordinarily  applied. 

287.  Characteristics  and  Distribution  of  Road-build- 
ing ROCKS.  Experience  in  France  and  Massachusetts  has  shown 
that  the  results  of  the  impact  and  abrasion  test  agree  reasonably 
well  with  the  relative  values  of  the  stones  as  determined  by  actual 
wear  in  the  road.  The  different  stones  are  arranged  in  Table  19  sub- 
stantially in  the  order  of  their  wear  in  the  impact  and  abrasion 
test,  and  consequently  this  order  represents  approximately  the 
relative  value  of  the  several  stones  for  road-building  purposes. 
However  there  are  some  exceptions  to  this  order.  Where  the 
traffic  is  light  a  hard  stone  may  not  furnish  enough  dust  to  re- 
place that  blown  away  by  the  wind  and  washed  away  by  the  water, 
and  also  to  bind  the  surface ;  and  in  such  case  a  softer  stone  or  one 
with  a  higher  cementing  power  may  be  preferable.     A  suitable 


ART.    1.]  THE    STONE.  191 

road  stone  should  be  soft  enough  to  grind  to  dust  only  slowly  under 
the  traffic,  and  this  dust  should 'have  a  high  cementing  power,  and 
the  separate  fragments  of  the  stone  should  have  strength  enough 
to  resist  the  crushing  action  of  the  wheels. 

The  characteristics  and  distribution  of  the  road-building  ma- 
terials which  are  extensively  available  will  now  be  briefly  con- 
sidered. 

288.  Trap.  This  is  a  popular  term  applied  to  any  dark-colored, 
massive,  igneous  rock.  Trap  is  very  compact  and  elastic,  has  a 
high  resistance  to  crushing  without  being  brittle,  and  its  dust  has 
the  cementing  power  in  a  high  degree.  The  different  traps  are 
not  uniformly  desirable,  but  nearly  all  of  them  are  better  than 
the  best  of  other  rocks;  and  therefore  the  traps  may  clearly  be 
placed  first  in  order  of  utility  among  road-building  stones. 

289.  Trappean  rocks  are  plentiful  in  the  greater  part  of  New 
England,  in  the  upland  districts  of  New  Jersey  and  the  neigh- 
boring portions  of  Maryland  and  Pennsylvania,  in  the  Blue  Ridge 
mountains  between  the  Potomac  and  the  James  rivers,  in  the  basin 
of  Lake  Superior,  particularly  in  the  northern  peninsula  of  Michigan, 
and  in  the  Rocky  mountains.  They  are  also  found  to  a  limited 
extent  in  southern  Missouri,  in  Arkansas,  and  in  central  Texas.* 
In  America  the  trap  rocks  are  not  as  plentiful  nor  as  evenly  dis- 
tributed as  in  Europe. 

The  traps  of  Table  19,  page  186,  include  eight  samples  from  New 
Jersey,  two  from  New  York,  two  from  Connecticut,  and  one  from 
Rhode  Island,  the  remainder,  forty-six,  being  from  Massachusetts. 

290.  Granite.  Next  in  value  to  the  trappean  rocks  are  those 
commonly  called  granites.  These  are  massive  granular  rocks 
composed  essentially  of  quartz  and  feldspar,  but  almost  always 
containing  mica,  hornblende,  and  other  components.  An  essen- 
tial feature  of  granite  is  an  evenly  granular  structure  coarse  enough 
to  be  distinctly  visible  to  the  naked  eye.  Granites  vary  widely, 
but  as  a  rule  they  are  inferior  road  material  owing  to  the  brittle- 
ness  of  both  the  quartz  and  the  feldspar,  and  also  to  their  coarsely 
granular  structure.  If  the  quartz  is  absent,  the  rock  is  what  is 
technically  called  syenite,  the  best  for  road  metal  of  the  so-called 

*  Shaler's  American  Highways,  p.  56-58. 


192  BROKEN-STONE    ROADS.  [CHAP.    Y. 


granites.  When  granite  is  free  from  mica,  it  offers  great  resistance 
to  wear.  If  the  granitic  rock  has  a  pronounced  fibrous  or  hairy 
arrangement  of  its  mineral  constituents,  the  rock  is  termed  gneiss, 
most  samples  of  which  are  very  inferior  road  materials. 

The  feldspar  of  granite  is  readily  decomposed,  producing  sand 
and  clay;  and  when  this  change  has  gone  on  to  a  considerable 
degree,  the  stone  should  be  discarded  as  unfit  for  road  material, 
since  it  readily  crumbles  to  sand  and  clay  under  the  action  of  frost 
and  traffic,  and  the  wind  sweeps  away  the  fine  material  in  dry 
weather,  and  in  rainy  times  the  road  is  in  a  muddy  state.  For 
this  reason,  granite  is  more  satisfactory  in  southern  than  in  northern 
localities. 

291.  "The  distribution  of  the  granite  rocks  is  unfortunately 
in  a  general  way  the  same  as  that  of  the  trappean  rocks  (§  289). 
Between  the  traps  and  the  granites  about  one  third  of  the  area  of 
the  United  States  is  fairly  well  provided  with  road-making  stones."  * 

292.  Limestone.  The  limestones  are  usually  deficient  in  hard- 
ness and  toughness,  but  possess  cementing  power  in  a  fair  degree 
(see  Tables  19  and  20).  Limestones  where  found  in  thin  layers 
with  little  sign  of  crystallization,  particularly  where  they  contain 
a  small  amount  of  clay, — say,  not  more  than  twenty-five  per  cent, 
— often  afford  tolerable  road  stones.  In  proportion  as  limestone 
becomes  crystalline,  i.  e.,  takes  on  the  character  of  marble,  its 
value  in  road-making  diminishes,  for  the  reason  that  the  crystalline 
structure  in  most  cases  so  far  weakens  the  mass  that  it  is  apt  readily 
to  pass  into  the  state  of  powder.  Marble  has  a  high  per  cent  of 
wear  and  a  low  cementing  power — see  Table  19.  Marbles  occur  only 
in  districts  where  better  road-making  materials  are  likely  to  be 
present. 

It  should  not  be  forgotten  that  the  limestones  in  Tables  19  and 
20  are  selected  samples  and  are  not  representative  of  the  whole 
series.     Some  limestones  are  entirely  too  soft  for  road  material. 

293.  The  limestones  are  the  most  widely  diffused  of  any  bedded 
rock  employed  for  road  purposes.  In  a  large  part  of  the  Missis- 
sippi Valley,  they  constitute  the  only  material,  except  glacial  drift, 
with  which  to  build  broken-stone  roads. 

*  Shaler's  American  Highways,  p.  58-59. 


ART.   1]  THE   STONE.  193 

294.  Sandstones.  As  a  rule  sandstones  are  worthless  as  road- 
making  materials,  being  deficient  in  binding  power  and  easily 
reducing  to  sand.  Notice  that  while  the  resistance  of  sandstone 
to  abrasion  and  impact  entitles  it  to  a  high  place  in  Table  19,  it  is 
very  low  in  cementing  power.  Occasionally  samples  are  found 
which  have  sufficient  binding  material  between  the  grains  to  hold 
the  mass  firmly  together  in  such  a  manner  as  to  render  it  a  fair 
road-building  material. 

Quartzite  was  originally  sand,  and  has  been  changed  into  a  com- 
pact mass  by  pressure  and  heat.  The  quartzites  differ  greatly, 
but  are  generally  too  soft  or  have  too  little  cementing  power  to 
make  a  good  road-building  material.  They  are  confined  to  com- 
paratively "  limited  areas,  being  found  principally  in  the  moun- 
tainous districts  of  the  Appalachian  and  Cordilleran  areas  and  in 
the  Adirondacks  and  the  Ozarks."  * 

Quartz  when  found  in  large  veins  sometimes  makes  a  fair  road 
metal.  It  is  very  hard  and  breaks  with  sharp  edges,  but  readily 
crushes  into  fine  dust  which  has  no  binding  power.  Roads  of 
this  material  rarely  attain  a  smooth  surface  and  always  wear  very 
rapidly. 

295.  Chert,  a  variety  of  quartz,  is  a  siliceous  material  with  the 
characteristics  of  flint,  but  differing  from  it  in  being  of  a  tougher 
nature,,  and  in  breaking  with  a  splintery  instead  of  a  conchoidal 
fracture.  Chert  has  a  variety  of  colors — red,  yellow,  gray,  and 
brown.  It  is  usually  mixed  with  more  or  less  lime,  and  beds  of 
chert  often  grade  imperceptibly  into  limestone.  Chert  varies 
greatly  in  quality,  and  being  brittle  and  somewhat  deficient  in  bind- 
ing power  it  is  never  a  first-class  road  stone,  but  will  usually  give 
fairly  good  results.  It  is  often  of  great  value,  since  it  occurs  in 
those  parts  of  the  country  where  good  road-building  material 
is  scarce  or  entirely  absent.  Chert  is  not  usually  found  in  a  solid 
mass,  but  in  a  finely  divided  state,  broken  ready  for  placing  upon 
the  road.     Chert  has  already  been  considered  as  a  gravel  (see  §  239). 

296.  Field  Stones.  In  the  glaciated  district  (see  §  238),  an  ex- 
cellent road  material  may  be  obtained  by  crushing  the  bowlders 
and  pebbles  that  are  too  coarse  for  use  in  gravel  roads. 

♦Shaler's  American  Highways,  p.  59. 


194  BROKEN-STONE    ROADS.  [CHAP.   V. 

"  Where  the  glacial  bowlders  have  lain  since  the  ice  time  exposed 
to  the  weather,  or  where,  being  of  small  size,  they  lie  in  the  zone 
to  which  decay  has  penetrated  from  the  surface,  they  are  often  so 
far  decomposed  as  to  be  essentially  unfit  for  use  in  road-making, 
save  it  may  be  as  telford  pavement,  or  as  a  bottom  coating  of 
broken  stone  which  is  to  be  covered  with  material  of  a  better  grade. 
The  variation  in  the  extent  to  which  decay  has  injuriously  affected 
the  surface  stone  may  be  judged  by  simple  tests  which  may  be 
readily  applied.  After  a  brief  experience  a  judicious  person  with 
a  light  sledge  hammer  can,  by  striking  the  stones,  readily  deter- 
mine the  state  of  the  masses.  If  they  ring  sharply  to  the  blow 
they  may  be  judged  sufficiently  sound.  If,  however,  they  pul- 
verize under  the  successive  strokes,  or  if  they  show  evident  traces 
of  decay,  as  by  iron  stains  penetrating  the  mass,  they  may  be  con- 
demned as  a  source  of  supply."  * 

There  is  inevitably  a  good  deal  of  difference  in  the  road  material 
obtained  from  bowlders  and  pebbles,  and  care  should  be  taken 
not  to  mix  the  hard  and  soft  varieties,  as  otherwise  the  road  will 
wear  unevenly.  If  the  different  varieties  are  laid  in  distinct  sec- 
tions, valuable  knowledge  may  thus  be  obtained  as  to  the  wearing 
qualities  of  the  different  grades. 

297.  Felsite.  This  is  a  hard  flinty  rock  having  about  the  same 
chemical  composition  as  granite,  but  which  to  the  unaided  eye 
appears  homogeneous.  It  is  frequently  classed  as  a  granite.  No- 
tice that  felsite  is  particularly  high  in  cementing  power — see 
Table  19. 

It  is  found  in  large  quantities  in  eastern  Massachusetts,  and  to 
some  extent  in  New  Hampshire,  Maine,  Pennsylvania,  Missouri, 
Minnesota,  and  Wisconsin. 

298.  Shale  and  Slate.  These  are  both  indurated  or  hardened 
clay.  These  terms  are  often  used  synonymously;  but  shale  is  less 
compact  than  slate,  and  will  not  split  into  slabs  and  sheets  as  does 
slate. 

Shale  is  the  most  abundant  of  all  stratified  rocks.  When  the 
clay  is  nearly  pure  it  is  called  argillaceous  or  clay  shale;  and  when 
it  contains  considerable  sand,  it  is  known  as  arenaceous  or  sandy 

♦Shaler's  American  Highways,  p.  69. 


ART.   2.]  CONSTRUCTION.  •     195 

shale.  The  shales  vary  in  color,  being  gray,  reddish,  or  very 
black.  For  road-building  purposes  the  argillaceous  shales  are  en- 
tirely worthless,  and  the  sandy  shales  are  useful  only  for  a  top 
dressing, — and  are  not  very  good  for  that. 

Slate  is  often  quite  hard  to  the  quarryman's  tools,  but  softens 
rapidly  in  contact  with  water.  As  a  road  material  the  fragments 
quickly  grind  to  dust  which  has  but  slight  binding  power.  Slate 
makes  a  smooth  road,  but  one  that  wears  very  rapidly,  particularly 
when  wet.  It  is  sometimes  used  as  a  surfacing  or  binding  ma- 
terial, but  is  much  inferior  to  clean  sand  or  good  stone  dust. 

299.  Conclusion.  Nearly  half  of  the  area  of  this  country — 
and  that  part  of  it  in  which  inheres  perhaps  nine  tenths  of  its  crop- 
giving  value — is  very  illy  provided  with  materials  fitted  for  high- 
way construction.  For  additional  information  concerning  the 
road-building  materials  of  the  United  States,  see  Preliminary 
Report  on  the  Geology  of  the  Common  Roads  of  the  United  States, 
by  Nathaniel  Southgate  Shaler,  in  U.  S.  Geological  Survey,  Fif- 
teenth Annual  Report,  1893-94,  p.  255-306. 

Art.  2.    Construction. 

300.  The  principles  of  construction  for  earth  roads  apply  also 
to  the  construction  of  the  subgrade  for  broken-stone  roads  (see  Art. 
1,  Chapter  III).  The  drainage  of  gravel  roads  by  tile  drains  and 
side  ditches  should  not  be  neglected  (see  §  98-109  and  §  110-13). 

301.  FORMS  OF  CONSTRUCTION.  With  reference  to  the 
method  of  preparing  the  subgrade  to  receive  the  stone,  there  are  two 
forms  of  construction — surface  construction  and  trench  construction. 
The  surface  construction  consists  simply  in  placing  a  layer  of 
broken  stone  upon  the  former  earth  road  and  leaving  it  to  be  com- 
pacted by  traffic.  In  the  West  many  miles  of  road  are  constructed 
on  this  plan  with  limestone.  As  a  rule  this  material  readily  pul- 
verizes under  the  traffic,  and  the  powder  cements  well;  conse- 
quently the  road  soon  binds  together.  Such  roads  are  not  first 
class  but  give  good  returns  on  their  cost.  On  account  of  the  sim- 
plicity of  the  construction,  this  form  of  road  will  not  be  considered 
further. 

The  trench  construction  consists  in  excavating  a  trench  of  the 
required  width  and  depth,  and  depositing  the  broken  stone  in  it. 


196  BROKEN-STONE   ROADS.  [CHAP.    V. 

302.  With  reference  to  the  lower  course  of  stone  there  are  two 
systems  of  construction, — the  macadam  and  the  telford,  so  called 
after  two  noted  English  road  builders  (§  274).  The  macadam 
road  consists  of  two  or  more  layers  of  crushed  stone,  its  distin- 
guishing characteristic  being  that  the  lower  course  of  crushed 
stone  is  placed  directly  upon  the  earth  road-bed.  The  telford 
road  consists  of  a  foundation  or  pavement  of  rough  stone  blocks 
set  upon  the  road-bed,  covered  with  one  or  more  layers  of  crushed 
stone,  the  distinguishing  feature  being  the  paved  foundation. 

303.  Telford  vs.  Macadam  Roads.  Each  of  these  systems 
has  its  earnest  advocates  who  contend  for  its  exclusive  use. 

(The  most  important  claims  of  the  advocates  of  the  telford 
construction  are:  (1)  that  the  open  foundation  is  necessary  for 
drainage;  (2)  that  the  sub-pavement  is  necessary  on  soft  or  poorly 
drained  soil  to  prevent  the  small  fragments  of  broken  stone  from 
working  down  into  the  soil  and  the  soil  from  working  up  into  the 
stone;  and  (3)  that  the  telford  is  the  cheaper,  since  the  expense 
of  crushing  is  saved. 

The  most  important  claims  of  the  advocates  of  the  macadam 
system  are:  (1)  that  the  drainage  afforded  by  the  telford  con- 
struction is  no  better  than  that  with  the  macadam  construction;  (2) 
that  on  any  well  drained  soil  there  is  no  tendency  of  the  stone  to 
work  down  or  of  the  soil  to  work  up;  (3)  that  tile  drainage  and 
macadam  construction  are  cheaper  than  the  telford  system ;  and 
(4)  that  since  the  introduction  of  the  machine  rock-breaker,  it  is 
cheaper  to  crush  the  stone  and  lay  the  macadam  foundation  than 
to  place  the  telford. 

The  view  taken  by  different  road  builders  in  this  matter  is 
probably  largely  due  to  the  necessities  of  the  vicinity  in  which 
they  have  worked  and  to  the  skill  with  which  the  two  systems 
have  been  applied  in  work  which  has  come  under  their  observation. 
The  foundation  which  is  proper  in  a  given  case  is  determined  by 
the  nature  and  condition  of  the  soil  upon  which  it  is  constructed. 
If  the  road-bed  is  thoroughly  drained  and  is  composed  of  material 
which  will  not  readily  soften,  there  will  be  no  need  of  a  telford 
foundation.  If,  on  the  other  hand,  the  soil  is  retentive  of  moisture 
and  can  not  be  thoroughly  drained,  it  may  be  necessary  to  provide 
a  foundation  which  will  prevent  the  soil  from  working  up  into 


ART.  2.]  CONSTRUCTION.  197 

the  stone  and  the  road  metal  from  working  down  into  the  soil. 
This  foundation  may  be,  according  to  the  intensity  of  the  difficulty 
to  be  met,  a  layer  of  sand  or  gravel,  or  a  telford  foundation  laid 
directly  on  the  soil,  or  a  telford  foundation  upon  a  layer  of  sand 
or  gravel.  The  choice  between  these  two  forms  of  construction, 
however,  often  depends  upon  the  kind  and  accessibility  of  materials. 
For  example,  a  soft  laminated  local  stone  may  be  used  for  a  telford 
foundation,  while  a  more  expensive  and  harder  stone  is  imported 
for  the  macadam  top. 

MacAdam  insisted  upon  a  foundation  of  small  fragments  under 
all  circumstances,  but  Telford  used  the  paved  foundation  only  as 
circumstances  seemed  to  require  it.  To  MacAdam  is  due  the  credit 
of  discovering  the  supporting  power  of  a  layer  of  comparatively 
small  angular  fragments  of  stone. 

304.  Forms  of  the  Subgrade.  The  finished  surface  of  the  road 
should  have  sufficient  crown  to  shed  the  rain  water  into  the  side 
ditches.  There  are  in  common  use  two  methods  of  securing  this 
crown.  In  one  the  earthen  surface  is  made  level,  and  the  slope  is 
given  by  a  greater  thickness  of  metaling  at  the  center  than  at  the 
sides;  in  the  other,  the  slope  or  camber  is  given  to  the  earth 
bed,  and  the  metal  has  a  uniform  thickness.  The  advocates  of 
the  first  system  say  that  there  is  more  wear  at  the  center  than  at 
the  sides,  and  that  consequently  the  metaling  should  be  thicker 
at  the  center.  Those  in  favor  of  the  uniform  thickness  say  that 
as  the  pressure  on  the  earth  is  practically  the  same  at  the  sides  as  at 
the  center,  the  thickness  should  be  uniform,  since  the  principal 
object  of  the  layer  of  stone  is  to  distribute  the  concentrated  pres- 
sure of  the  wheel  over  a  greater  surface  of  the  earth  bed.  Both 
forms  of  construction  are  in  common  use,  although  the  preference 
seems  to  be  slightly  in  favor  of  making  the  subgrade  parallel  to 
the  finished  road-surface  and  the  stone  of  uniform  thickness.  A 
level  subgrade  is  slightly  cheaper  to  form. 

Tresaguet,  a  Frenchman,  seems  to  have  originated  in  1764 
the  system  of  making  the  subgrade  parallel  to  the  finished  road 
surface.  Telford  finished  the  subgrade  level,  while  MacAdam 
made  it  parallel  to  the  surface  of  the  road.  Tresaguet  used  the 
form  of  foundation  now  known  as  telford. 

Fig.  45,  page  198,  shows  a  cross  section  of  the  celebrated  Shrews- 


198 


BROKEN -STONE    KOADS. 


[CHAP.   V. 


bury  and  Holyhead  road  in  the  west  of  England,  built  by  Telford 
in  1815.  The  construction  of  this- road,  which  formed  a  link  in 
the  direct  line  of  communication  between  England  and  Ireland, 


Fig.  45.— Telford's  Shrewsbury  and  Holyhead  Road. 

was  made  a  national  undertaking,  and  resulted  in  what  was  at  that 
time  one  of  the  finest  pieces  of  road  construction  in  the  world. 

The  Swiss  roads  shown  in  Fig.  55  and  56,  page  210,  have  a  level 
•ubgrade. 

14ft. 


K-—   7  ft H< 

I  I 

!  !  rJn 


nritStmtgfr 


Ik  in.  Stones 


>k 7ft ** 

i  • 

!  ,'3in.  \ 

L'/3in 


ML 


Fig.  46.— Modern  Telford  Road  as  Built  in  New  Jersey. 

Fig.  46  shows  a  Tresaguet  or  "  modern  telford  "  road  as  built 
in  New  Jersey.  Notice  that  the  base  of  the  foundation  is  parallel 
to  the  surface  of  the  finished  road. 

305.  Maximum  Grades.  For  examples  of  steep  grades  on 
broken-stone  roads,  see  §  82. 

306.  Width.  In  view  of  the  considerable  cost  necessarily  in- 
volved in  constructing  a  first-class  broken-stone  road,  it  is  impor- 
tant to  determine  the  width  that  should  be  paved.  The  width  of 
way  necessary  for  ordinary  rural  traffic  is  often  over-estimated. 
Two  wagons  having  a  width  of  wheel  base  of  5  feet  and  a  width  of 
load  of  9  feet  can  pass  on  a  16-foot  roadway  and  leave  6  inches 
between  the  outer  wheel  and  the  edge  of  the  paved  way  and  a 
clearance  of  1  foot  between  the  inner  edges  of  the  loads.  This 
extreme  case  will  rarely  occur,  and  hence  a  width  of  16  feet  will 
certainly  be  enough  unless  there  is  considerable  rapid  traffic. 

The  Massachusetts  Highway  Commission  carefully  measured 
the  width  of  traveled  way  on  numerous  crushed-stone  roads,  and 
found  that  with  an  improved  width  of  15  to  24  feet, — the  average 
being  16.1  feet, — the  maximum  width  of  traveled  way  averaged 


ART.   2.]  CONSTRUCTION.  199 

14.92  feet  and  the  width  commonly  traveled  averaged  11.05  feet.* 
On  this  evidence  the  Commission  concludes  that  "  a  width  of  15 
feet  is  ample  except  in  the  vicinity  of  the  larger  towns,  and  that 
12  feet  is  sufficient  for  the  lighter  traveled  ways,  but  that  10  feet 
is  too  narrow  Unless  good  gravel  can  be  obtained  for  the  shoulders."f 
The  average  width  commonly  traveled  on  forty-six  of  the  15-foot 
roads  was  9.58  feet. 

In  New  Jersey  the  width  for  state-aid  roads  is  9  to  16  feet, 
mostly  10  to  12  feet.  The  improved  width  of  French  roads  varies 
from  16  to  22  feet  (see  §  89);  in  Austria,  from  14  to  26  feet;  and 
in  Belgium  there  are  many  roads  only  8J  feet  wide. 

307.  Earth  Shoulders.  The  preceding  discussion  has  referred 
only  to  the  width  of  the  paved  portion;  but  there  should  be  an 
additional  width  of  earth  sufficient  to  keep  the  broken  stone  in 
place,  particularly  while  being  rolled.  This  strip  of  earth  is  usu- 
ally called  a  shoulder,  but  sometimes  and  improperly  a  wing  (see 
§  322).  The  proper  width  of  the  shoulder  will  depend  upon  the 
soil,  the  climate,  and  the  amount  of  rolling  it  receives.  Usually 
2  or  3  feet  is  sufficient,  although  5  to  7  feet  is  frequently  provided 
— see  Fig.  46.  The  Swiss  road  shown  in  Fig.  55,  page  210,  has  a 
shoulder  of  only  18  inches.  Compare  Fig.  50-54,  pages  209-10,  and 
Fig.  57  and  58,  page  211.  An  excess  width  of  shoulder  adds  greatly 
to  the  cost  of  the  road  wThen  in  excavation  or  on  embankment. 
The  surface  of  the  shoulder  should  conform  to  the  general  curve 
of  the  finished  roadway.  The  earth  shoulder  serves  the  double 
purpose  of  holding  the  broken  stone  in  place  and  of  affording 
room  for  vehicles  in  passing  each  other.  To  improve  the  shoulders 
for  the  second  purpose,  they  are  sometimes  covered  with  a  thin 
coat  of  gravel  to  harden  the  surface.  Sand  shoulders  are  speedily 
hardened  by  the  infiltration  of  fine  stone  dust  and  dirt  washed 
from  the  surface  of  the  road.  This  effect  is  quite  noticeable  with 
coarse  sand;  and  is  appreciable  even  with  fine  sand. 

303.  CROWN.  The  center  of  the  road  should  be  higher  than  the 
sides,  so  that  the  water  from  rains  may  flow  rapidly  into  the  side 
ditches.     If  originally  too  flat,  the  road  is  soon  worn  hollow,  and 

*  Report  of  the  Massachusetts  Highway  Commission  for  1897,  p.  31.    For  a  sum- 
mary of  similar  data  for  each  township  for  five  years,  see  Report  for  1901,  p.  47-55. 
t  lUd.,  1900,  p.  32. 


200  BROKEN-STONE   ROADS.  [CHAP.  Y. 

the  middle  becomes  a  pool  if  on  level  ground,  or  a  water  course 
if  on  an  inclination.  In  the  former  case  the  middle  of  the  road  is 
sloppy;  and  in  the  latter,  the  fine  material  washes  away  and  leaves 
the  larger  stones  bare.  There  has  been  much  discussion  both  as  to 
the  proper  amount  of  crown  and  the  exact  form  of  the  transverse 
profile  of  the  roadway. 

309.  Form  of  the  Profile.  Some  claim  that  the  upper  surface 
should  be  an  "  arc  of  a  circle  or  a  flat  ellipse";  and  others,  that  it 
should  be  two  inclined  planes  meeting  at  the  center  of  the  road 
and  having  their  angle  slightly  rounded  off.  Both  forms  are  in 
common  use;  the  first  is  the  more  common,  but  apparently  the 
latter  is~  the  better. 

The  following  objections  are  urged  against  the  curved  profile: 
1.  The  greater  slope  near  the  side  causes  vehicles  to  seek  the  center, 
and  consequently  the  road  wears  unequally.  2.  Owing  to  the  ex- 
cess of  traffic  at  the  center,  the  road  soon  wears  hollow  and  holds 
water,  which  is  both  unsightly  and  a  damage  to  the  road.  3.  The 
slope  is  so  slight  near  the  center  that  a  small  settlement  of  the 
subgrade  causes  a  depression  of  the  surface,  which  holds  water. 

The  only  objection  to  a  surface  composed  of  two  planes  is  that 
the  flanks  wear  hollow  and  hold  water;  but  this  objection  has  less 
force  than  any  of  the  three  against  the  curved  profile. 

310.  Curved  Profile.  Although  the  curved  profile  is  usually 
referred  to  as  being  "  an  arc  of  a  circle  or  a  flat  ellipse/ '  it  is  usu- 
ally laid  out  as  the  arc  of  a  parabola.  However,  the  difference 
of  curvature  is  not  material. 

To  lay  out  the  parabolic  arc  proceed  as  follows:  In  Fig. 47,  AC 
is  the  crown,  i.  e.,  the  difference  in  height  between  the  side  and 
the  center.  AB  represents  a  horizontal  line  through  the  crown. 
In  street  pavements  A  is  usually  the  top  of  the  curb.     The  curved 


line  BC  represents  the  surface  of  the  finished  road.  To  find  the 
distance  from  AB  down  to  the  line  BC,  divide  the  half  width  of 
roadway,  AB,  into  any  number  of  equal  parts,  say,  n,  and  desig- 


ART.   2.]  CONSTRUCTION.  201 

nate  the  distance  from  the  point  1  on  AB  vertically  down  to  BC 

AC 
by  x;  then  by  the  principles  of  the  parabola,  x  =  —  ~,  and  the  dis- 

tance  from  point  2  down  to  the  road  surface  is  22  x  or  4  x,  and  the 
distance  from  3  is  32  x  or  9  x.  In  practice  a  string  with  knots  in  it 
to  represent  the  points  of  division  of  A B  is  stretched  from  the  top 
of  the  curbs  or  from  stakes  driven  at  the  edge  of  the  broken  stone, 
and  then  the  ordinates  coinputed  as  above  are  measured  with  a 
pocket  rule. 

311.  There  are  a  number  of  arbitrary  rules  for  securing  a  curved 
profile,  of  which  the  following  is  one  of  the  most  elaborate,  the 
most  scientific,  and  the  most  easily  remembered :  "  Divide  the  half 
roadway  into  three  equal  parts,  and  starting  from  the  center  give 
a  fall  of  0.03  ft.  per  foot  for  the  first  part,  0.04  ft,,  for  the  second 
section,  and  0.05  ft.  for  the  last  section.  If  the  roadway  is  ex* 
tremelywide,  divide  the  half  roadway  into  four  parts,  and  give 
a  fall  of  0.02,  0.03,  0.04,  and  0.05  ft.  per  foot  to  the  respective 
sections.  If  the  roadway  is  very  narrow,  divide  the  half  roadway 
into  two  parts,  and  give  falls  of  0.04  and  0.05  ft.  per  foot  to  the 
two  sections  respectively." 

This  rule  gives  more  slope  at  the  center  and  less  at  the  sides 
than  the  parabolic  section,  and  for  roadways  of  medium  width, 
it  gives  an  average  transverse  slope  of  half  an  inch  to  the  foot  or 
1  in  24.  This  rule  was  used  on  the  road  shown  in  Fig.  50,  page 
209. 

312.  Two-plane  Profile.  When  the  surface  consists  of  two 
planes  meeting  at  the  center,  the  profile  is  very  easily  constructed 
or  tested.  In  Fig.  48,  AC  represents  the  crown  or  difference  be- 
tween the  side  and  the  center,  CB  is  the  finished  surface,  and  AB 
is  a  horizontal  line.     Divide  the  half  width  AB  into  n  equal  parts, 


Fig.  48.— Two-plane  Surface. 

AC 
and  then  the  ordinate  from  point  1  down  is  — ,  and  that  from  2  is 

n 

2 ,  and  that  from  3  is  3 — ,  etc. 

n  n 


202  BROKEN-STONE    ROADS.  [CHAP.    V. 

Regularity  and  evenness  of  crown  is  more  important  than  the 
mathematical  form  of  the  cross  section.  A  slight  depression  be- 
comes very  conspicuous  when  filled  with  water;  and  besides  the 
water  standing  upon  the  surface  softens  it  and  tends  to  increase 
the  depression.  With  a  little  care  in  filling  the  low  places  devel- 
oped during  the  rolling,  it  is  possible  to  build  a  broken-stone  road 
with  an  almost  mathematically  exact  crown. 

313.  Amount  of  Crown.  The  proper  amount  of  crown  depends 
chiefly  upon  the  method  of  making  repairs.  If  new  material  is 
added  only,  say,  each  second  or  third  time  the  surface  is  smoothed 
up,  then  the  crown  should  be  greater  to  compensate  for  future 
wear;  but  if  new  material  is  added  practically  continuously, 
the  crown  may  be  considerably  smaller.  The  rate  of  transverse 
slope  should  be  smaller  on  wide  than  on  narrow  streets,  to  prevent 
the  water  from  unduly  washing  the  surface  near  the  sides.  There 
should  be  more  crown  on  steep  grades  than  on  flat  ones,  to  throw 
the  water  quickly  to  the  side  ditch  and  to  prevent  it  from  flowing 
down  the  grade  on  the  surface  of  the  road  and  washing  out  the 
binder. 

Sometimes  wide  boulevards,  with  curved  profile  and  main- 
tained by  continuous  repairs,  have  a  crown  of  one  sixtieth  of  the 
width,  or  a  rise  of  0.4  inch  per  foot  from  side  to  center,  or  an 
average  slope  of  1  in  30.  The  French  roads,  which  have  a  curved 
profile  and  are  maintained  by  the  system  of  continuous  repairs, 
have  a  crown  of  one  fiftieth  of  their  width,  or  a  rise  from  side  to 
center  of  0.5  inch  per  foot  or  a  slope  of  1  in  25.  Many  of  the  better 
cared  for  streets  and  park  drives  have  a  crown  of  one  fortieth,  or 
a  rise  from  side  to  center  of  0.6  inch  per  foot  or  an  average  slope 
of  1  in  20.  On  the  state-aid  roads  in  Massachusetts  (narrow  roads 
and  continuous  repairs),  the  surface  consists  of  two  planes  meeting 
in  the  center,  the  transverse  slope  being  f  inch  to  a  foot  or  1  in  16. 
Broken-stone  roads  made  of  soft  stone  and  maintained  by  periodic 
repairs  frequently  have  an  original  crown  of  one  twelfth — an 
average  slope  of  1  inch  to  1  foot  or  1  in  12. 

In  Providence,  R.  I.,  the  following  relation  between  the  grade 
and  the  crown  has  been  established: 


ART.   2.]  CONSTRUCTION.  203 

LONGITUDINAL   SLOPE.  TRANSVERSE    SLOPE. 

i  to  4  per  cent  1  in  25 

4  to  6   "      "  lin20 

6  to  9   w     "  linl2J 

314.  With  a  broken-stone  road,  the  method  of  making  repairs 
has  more  weight  in  determining  the  amount  of  the  crown  than 
in  the  case  of  either  an  earth  road  or  a  gravel  road.  The  earth 
road  is  easily  and  cheaply  maintained  by  what  may  be  called  the 
system  of  continuous  repairs  with  the  scraping  grader,'  which 
restores  or  rather  maintains  the  crown.  With  a  gravel  road, 
when  it  is  necessary  to  restore  the  crown  by  adding  more  gravel,  it 
is  usually  sufficient  to  put  on  only  a  thin  layer  and  wait  a  com- 
paratively short  time  for  traffic  to  consolidate  it.  With  a  broken- 
stone  road,  if  the  crown  or  rather  the  surface  is  to  be  perpetually 
maintained,  it  is  necessary  to  keep  a  man  upon  a  short  stretch  of 
the  road  practically  all  of  the  time,  adding  thin  patches  of  stone 
in  first  one  place  and  then  another,  a  method  so  expensive  that 
it  is  practiced  in  this  country  only  on  park  drives,  boulevards,  etc.; 
and  if  the  crown  is  to  be  restored  periodically,  it  is  necessary  to 
add  a  considerable  layer  of  stone  and  consolidate  it  by  long  con- 
tinued and  expensive  rolling  and  sprinkling,  and  on  account  of 
the  expense  of  this  operation  and  the  obstruction  to  traffic  it  is 
customary  to  lay  such  a  thickness  of  stone  and  to  give  the  surface 
such  a  crown  as  not  soon  to  require  a  repetition  of  the  process. 
Therefore  it  happens  that  broken-stone  roads  are  often  built  with 
a  crown  nearly,  if  not  quite,  equal  to  that  of  good  earth  roads, 
and  with  more  perhaps  than  is  given  to  good  gravel  roads. 

315.  There  is  a  slight  advantage  of  a  very  high  crown  for  a  broken- 
stone  road,  particularly  for  one  that  is  not  frequently  cleaned.  If 
the  crown  is  great,  the  rains  will  the  better  wash  the  surface  clean. 
Dirt  upon  the  surface  is  not  only  unsightly,  but  is  also  detrimental 
since  it  holds  the  water  and  softens  the  surface.  Of  course  the 
material  washed  by  rains  into  the  gutter  must  eventually  be  re- 
moved; but  this  can  be  removed  more  cheaply  from  the 
gutter  with  a  scraping  grader  at  comparatively  long  intervals, 
than  from  the  surface  with  brooms  or  scrapers  at  short  in- 
tervals.    The  practice  of  making  a  high  crown  is  somewhat  com' 


204 


BROKEN-STONE    ROADS. 


[CHAP.   V. 


mon  in  villages  using  soft  road  metal  and  having  eart^  gutters 
and  only  surface  drainage. 

This  advantage  of  a  high  crown  is  less  for  a  country  road  than 
for  a  village  street,  since  the  wind  usually  gets  a  better  sweep 
at  the  former  than  at  the  latter. 

316.  Road  Level.  The  transverse  curvature  of  the  surface 
of  the  road  may  be  tested  by  the  use  of  the  instrument  shown  in 
Fig.  49.  It  consists  of  a  straight  edge,  E  F,  about  8  feet  6 
inches  long  made  of  a  1-inch  by  6-inch  pine  plank,  surmounted  by 
a  frame  which  serves  as  a  handle  and  to  support  the  plumb-line. 


Fig.  49.— Road  Level. 


The  general  construction  is  sufficiently  shown  in  Fig.  49.  The 
plumb-bob  can  be  bought  at  any  hardware  store  for  a  few  cents. 
On  the  front  side  of  the  piece  A  B,  is  screwed  a  piece  C  D,  the  middle 
half  of  the  back  of  which  is  cut  out  just  enough  to  leave  room  for 
the  plumb-line  to  swing. 

To  adjust  the  instrument  proceed  as  follows:  Drive  two  nails 
8  feet  4  inches  apart  into  the  floor  with  their  heads  at  approxi- 
mately the  same  level.  Set  the  straight  edge  E  F  upon  the  nails, 
and  make  a  temporary  mark  on  the  upper  edge  of  A  B  or  C  D  to 
indicate  the  position  of  the  plumb-line;  then  reverse  the  straight 
edge  end  for  end,  and  again  mark  the  position  of  the  plumb-line. 
Make  a  permanent  mark  square  across  the  top  of  both  A  B  and 
C  D  midway  between  the  two  temporary  marks,  and  drive  down 
the  higher  nail  until  the  plumb-line  hangs  opposite  this  mark; 
then  the  lower  edge  of  E  F  is  exactly  level. 

To  fit  the  above  instrument  for  use  in  testing  the  crown  of  a 
road,  it  is  necessary  either  (1)  to  fasten  upon  the  piece  E  F  a  board 


ART.   2.]  CONSTRUCTION.  205 

whose  lower  edge  is  cut  to  the  proper  curve,  or  (2)  to  attach  strips 
the  ends  of  which  indicate  points  on  the  curved  profile.  If  the 
first  method  is  employed,  the  curvature  of  the  lower  edge  of  the 
template  may  be  determined  by  the  method  of  §  310;  and  if  the 
second  method  is  preferred,  the  amount  that  the  several  strips 
should  project  beyond  the  edge  of  E  F  may  be  computed  by  the 
method  of  §  310.  If  the  strips  are  used,  it  is  most  convenient  to 
slot  them  and  attach  them  with  round-headed  wood  screws,  so 
that  the  strips  may  be  more  accurately  adjusted  to  position. 

The  instrument  is  of  use  to  an  inexperienced  person  in  inspect- 
ing the  curvature  of  the  crown  of  a  broken-stone  road. 

317.  The  above  instrument  may  easily  be  modified  so  as  to  be 
of  service  in  inspecting  the  longitudinal  slope  of  the  side  ditches, 
for  which  purpose  neither  the  strips  projecting  below  the  straight 
edge  nor  the  template  are  required.  Without  these,  the  instru- 
ment is  simply  a  level,  and  it  only  remains  to  graduate  it.  This 
may  be  done  as  follows:  Proceeding  as  in  the  second  paragraph 
of  §  316,  drive  two  nails  into  the  floor  until  they  are  exactly  at  the 
same  level;  and  then  adjacent  to  one  of  these  nails,  drive  another 
until  its  head  is  exactly  1  inch  above  the  adjoining  one.  Set  the 
straight  edge  E  F  upon  this  and  the  opposite  nail,  and  mark  the 
position  of  the  plumb-line.  The  lower  edge  of  E  F  is  now  on  a 
grade  of  1  inch  in  8  feet  4  inches,  or  1  inch  in  100  inches,  or  1  foot 
in  100  feet.  By  obvious  modifications  of  the  above  process,  the 
upper  face  of  either  the  piece  A  B  or  CD  can  be  graduated  to 
correspond  to  any  grade. 

In  this  form,  the  instrument  is  of  material  help  in  determining 
whether  the  bottom  of  a  ditch  has  a  uniform  grade.  The  instru- 
ment is  not  capable  of  mathematical  precision,  and  hence  should 
not  be  employed  to  run  long  lines  of  levels  when  accuracy  is  re- 
quired ;  but  it  is  valuable  in  checking  the  grade  between  points 
determined  by  an  engineer's  leveling  instrument.  To  obtain  the 
highest  accuracy,  the  plumb-line  should  be  fine  and  smooth. 

318.  THICKNESS.  The  object  of  placing  a  layer  of  broken 
stone  upon  the  trackway  is  to  secure  (1)  a  smooth  hard  surface . 
(2)  a  water-tight  roof,  and  (3)  a  more  or  less  rigid  stratum  which 
will  distribute  the  concentrated  pressure  of  the  wheel  over  an  area 
of  the  subgrade  so  great  that  the  soil  can  support  the  load  without 


206  BROKEN-STONE   ROADS.  [CHAP.  V. 

indentation.  The  smooth  surface  and  the  tight  roof  depend  upon 
the  quantity  and  quality  of  the  binding  material  (§  345-49);  and 
the  rigidity  of  the  layer  depends  somewhat  upon  the  binder,  but 
chiefly  upon  the  thickness  of  the  stratum.  The  supporting  power 
of  the  subgrade  depends  upon  the  nature  of  the  soil  and  particularly 
upon  the  drainage.  Therefore  the  minimum  thickness  of  broken 
stone  depends  upon  the  nature  of  the  soil,  the  drainage,  the  traffic, 
and  the  binding  material;  and  the  initial  thickness  depends  upon 
the  amount  of  wear  permitted  before  new  material  is  added.  If 
repairs  are  continuous,  the  initial  thickness  may  be  the  mini- 
mum; but  if  repairs  are  made  periodically,  the  initial  thickness 
must  be  equal  to  the  minimum  thickness  plus  the  amount  allowed 
for  wear.  After  a  road  has  been  worn  down  3  inches,  it  is  usually 
so  uneven  as  to  require  re-surfacing;  and  therefore  it  is  uneconom- 
ical if  the  road  in  this  stage  is  much  or  any  thicker  than  the  mini- 
mum required  to  prevent  its  breaking  through. 

There  has  been  much  discussion  and  there  is  a  great  difference 
of  opinion  as  to  the  proper  depth  of  a  broken-stone  road.  The 
depth  considered  necessary  by  the  most  extreme  advocates  of 
thick  roads  has  decreased  with  the  introduction  of  more  improved 
methods  of  construction — particularly  the  use  of  binder  and  a 
steam  roller, — and  as  the  advantage  of  thorough  under-drainage 
has  been  better  appreciated.  Early  in  the  last  century  a  depth  of  18 
to  24  inches  was  frequently  considered  necessary  for  heavy  traffic, 
but  later  it  was  reduced  to  12  or  15  inches,  while  now  6  inches,  or 
less,  is  usually  considered  sufficient. 

319.  The  concentrated  load  of  a  wheel  is  transmitted  through 
the  broken  stone  to  the  earth  in  lines  diverging  downward,  and  the 
wheel  may  be  assumed  as  resting  upon  the  apex  of  a  cone  whose 
base  is  upon  the  earth  subgrade.  The  sides  of  this  cone  probably 
make  an  angle  of  about  30°  with  the  vertical*  It  is  not  wise  to 
attempt  to  find  a  mathematical  relation  between  the  load  on  the 
wheel  and  the  resulting  pressure  on  tho  earth,  since  neither  the 
angle  of  the  cone  nor  the  distribution  of  the  pressure  on  the  base 
of  the  cone  are  known.     It  is  reasonably  certain,  however,  that 

*  For  information  of  a  little  interest  in  this  connection,  see  §19  of  Materials  of 
Construction  by  Prof.  J.  B.  Johnson.     New  York,  1897. 


ART.  2.]  CONSTRUCTION.  207 


the  supporting  power  of  a  crushed-stone  road  varies  as  the  square 
of  the  depth.  This  is  an  important  relation  to  bear  in  mind  when 
a  road  is  to  be  strengthened. 

The  Massachusetts  Highway  Commission  assumes  *  the  pressure 
to  be  uniformly  distributed  over  an  area  equal  to  the  square  of 
twice  the  thickness  of  the  layer  of  crushed  stone,  which  is  equiva- 
lent to  assuming  that  the  sides  of  the  cone  make  an  angle  of  48^ 
degrees  with  the  vertical  and  that  the  pressure  is  uniformly  dis- 
tributed over  the  base.  According  to  this  theory,  if  t  =  the  thick- 
ness of  the  stone  in  inches,  w  =  the  maximum  weight  in  pounds 
per  wheel,  and  p  =  the  supporting  power  of  the  soil  in  pounds 
per  square  inch,  then 


■ri 


R id 

4p 


The  Commission  has  applied  this  formula  to  roads  already  con- 
structed to  determine  the  safe  bearing  power  of  the  soil,  and  con- 
cludes that  non-porous  soils,  drained  of  ground  water,  at  their 
worst  will  support  a  load  of  4  pounds  per  square  inch,  and  that 
sand  and  gravel  will  safely  support  20  pounds  per  square  inch.f 

Although  the  method  of  arriving  at  equation  (1)  is  not  correct, 
the  manner  of  deducing  the  supporting  power  of  the  soil  in  a  meas- 
ure offsets  the  error,  and  consequently  the  formula  may  be  used 
with  some  confidence. 

320.  In  Massachusetts  the  thickness  for  state-aid  roads  varies 
from  4  to  16  inches,  the  standard  for  crushed  stone  with  macadam 
foundation  on  well  drained  sand  or  gravel  being  6  inches,  "  which 
appears  to  be  ample  for  the  heaviest  traffic. "t 

In  New  Jersey,  on  state-aid  roads,  the  depth  of  stone  with 
macadam  foundation  varies  from  4  to  12  inches,  but  is  generally 
6  iiches;  and  the  telford  roads  are  from  8  to  12  inches  thick,  usu- 
ally 8  inches.  Most  of  the  roads  have  a  macadam  foundation, 
the  telford  being  used  as  a  rule  only  where  field  stones  suitable 
for  a  telford  foundation  are  found  alongside  of  the  road. 

*  Annual  Report  for  1901,  p.  15. 

f  Massachusetts  Highway  Commission,  Report  for  1901,  p.  15. 

%Ibid.,W00,  p.  32. 


308  BROKEN-STOXE    ROADS.  [CHAP.    V. 

321.  The  experience  at  Bridgeport;  Conn.,  is  frequently  cited 
to  prove  that  a  comparatively  thin  road  is  sufficient.  Something 
like  60  miles  of  4-inch  macadam  roads  built  in  that  place  gave 
Excellent  service  even  under  a  heavy  traffic.  The  conditions 
were  very  favorable  for  a  thin  road:  (1)  the  soil  was  sand  or  sandy 
loam,  and  had  fairly  good  natural  drainage;  (2)  the  subgrade  was 
thoroughly  rolled  with  a  15-ton  roller;  (3)  the  broken  stone  was 
trap,  which  is  hard  and  durable;  (4)  the  binder  was  hard  and 
durable,  being  either  stone  dust  or  siliceous  sand,  and  was  free 
from  clay  or  loam;  (5)  the  binder  was  worked  in  until  the  voids  in 
the  crushed  trap  were  practically  filled,  the  effect  of  frost  being  thus 
reduced  to  a  minimum  and  the  soil  being  prevented  from  working 
up  from  below;  (6)  the  stone  was  thoroughly  consolidated  with 
a  steam  roller  of  adequate  weight;  and  (7)  the  roads  were  main- 
tained by  the  system  of  continuous  repairs. 

The  experience  at  Bridgeport  has  been  repeated  at  several 
other  places;  but  such  experiences  should  be  regarded  as  the  ex- 
ception, rather  than  the  rule,  since  4-inch  roads  are  adequate  only 
under  favorable  natural  conditions  and  with  the  most  painstaking 
construction  and  careful  maintenance.  The  fact  that  a  very  thin 
road  can  carry  the  traffic  does  not  prove  that  such  a  road  is  the 
most  economical,  for  the  increased  cost  of  maintenance  may  more 
than  counter-balance  the  decreased  cost  of  construction.  The 
engineer  should  always  attempt  to  construct  economically  and 
adapt  his  construction  to  fit  the  natural  conditions. 

In  many  cases  the  problem  is  whether  to  construct  a  thick 
road  on  the  undrained  soil  or  to  secure  thorough  underdrainage 
and  build  a  thin  road.     The  latter  is  usually  better  and  cheaper. 

322.  Wings.  In  the  preceding  discussion  of  the  thickness  of 
the  road  metal  it  has  been  assumed  that  the  depth  was  practically 
uniform;  but  some  engineers,  in  recognition  of  the  fact  that  there 
is  less  travel  nearer  the  sides  than  at  the  center,  make  the  thick- 
ness of  a  strip  on  each  side  considerably  less  than  that  at  the  center. 
The  thin  strips  on  the  sides  are  called  wings.  Fig.  50,  page  209,  a 
portion  of  the  Swedesboro  road  in  Gloucester  County,  New  Jer- 
sey, shows  a  cross  section  of  this  form.  This  construction  is 
somewhat  common  in  New  Jersey,  both  with  telford  and  macadam 
foundations,  and  has  been  adopted  by  the  U.  S.  A.  engineers  for 


ART.  2.] 


CONSTRUCTION. 


209 


macadam  roads  in  Porto  Rico.*  The  wings  are  usually  2  or  2\ 
feet  wide.  A  road  with  wings  is  simply  a  compromise  between 
a  narrow  thick  road  and  a  wide  thin  one. 


—  .7*1 *^25ff^ 9  ft. pf2Jft\* 


Fig.  50.— New  Jersey  Telford  Road  with  Macadam  Wings  . 

323.  examples  of  Cross  Sections.  Fig.  45,  page  198,  shows 
a  cross  section  of  a  telford  road  built  under  Telford's  direction  in 
1815.  Fig.  46,  page  198,  shows  a  New  Jersey  telford  road.  Fig. 
50  shows  a  telford  road  with  macadam  wings.     Fig.  51  shows  the 


I 


l.f4ft.-* ZOftto26ff Rolled +H4ff.~*p 

K* 12  ft  to  16  ft p\ 


I 


Fig.  51.— Standard  Section  for  New  York  State-aid  Roads. 

standard  cross  section   for   state-aid   roads  in  the  state  of  New 
York.f    Fig.  52  is  a  section  of  a  road  in  Flushing,  Long  Island, 

ffty*3ft-^3ft-^  4.5ft  -??-  45ft -x*  45ft  ->^  45 ft -^-3 ft ->f 5ft -^? ft \ 
faff\l ^ggg  t  j  a        [/OfSft     \j0.4ft\ 


Fig.  52.— General  Section  of  Flushing  and  Jamaica  Road. 

near  New  York  City.  This  road  is  crowned  according  to  the 
rule  stated  in  §  311.  Fig.  53  and  54,  page  210,  are  the  standard 
cross  section  in  excavation  and  on  embankment,  respectively,  for 
state-aid  roads  in  Massachusetts. {  "These  are  the  sections 
generally  employed,  but  may  be  modified  to  suit  the  conditions; 
for  example,  the  thickness  of  the  crushed  stone  may  be  made 
either  less  or   more   than   shown,  if  the  local  conditions  justify; 

*  Engineering  News,  Vol.  45,  p.  202. 

f  Report  of  the  State  Engineer  and  Surveyor,  1899,  p.  321 ;  or  Bulletin  No.  1, 
April  1899,  p.  9. 

J  From  official  drawings,  by  courtesy  of  Austin  B.  Fletcher,  Secretary  of  the 
Massachusetts  Highway  Commission. 


210 


BROKEN-STONE    EOADS. 


[CHAP.   V. 


21ft 


Fig.  53.— Standard  Section  in  Excavation  for  Massachusetts  State -aid  Roads. 


I  .-12  in 

^2ii?x6i\f. 


25  ft 


LONGITUDINAL  SECTION 
Fig.  54.— Standard  Section  on  Embankment  for  Massachusetts  State-aid  Roads. 

and  where  very  heavy  soil  is  encountered,  2  inches  of  gravel  are 
put  under  the  telford." 


•Ill  -lfl-lft.~l5ft 


Fig.  55.— Class-II  Road,  Canton  of  Bern,  Switzerland. 

Fig.  55  and  56  show  sections  of  two  Swiss  roads.* 

XtsnX 

it)..'--— 

Fig.  56.— Class-III  Road,  Canton  of  Bern,  Switzerland. 

*  Special  Consular  Reports  on  Streets  and  Highways   in  Foreign  Countries, 
A,  partment  of  State,  U.  S.  A.,  1897,  p.  238. 


ART.   2.] 


CONSTRUCTION. 


211 


Fig.  57  shows  a  typical  road  in  the  Department  of  Bas-Rhin, 
France.*  The  broken  stone  is  6  inches  deep,  19  feet  8  inches 
wide,  and  has  a  crown  of  one  fiftieth. 


Slope  Hoi  Slopeltol  -*  '/%%%>. 

Fig.  57.— Typical  Road  in  Department  of  Bas-Rhin,  France. 

Fig.  58  is  a  typical  French  road  in  the  Department  of  Seine-et- 
Oise.*  The  crown  of  the  roadway  is  one  fortieth,  and  the  trans- 
verse slope  of  the  sidewalks  is  1  in  20. 

W-6ft  7/n-  ^3fl4ir^ 8ft  J//?--*~* — 8ft  3in. — ->\3ft4Jn*<—6fT77r?—*i 

I  I  I  > 

I  I 

I  '7n 


Fia.  .iS.— Typical  Road  in  Department  op  Seine-et  Oise,  France. 

324.  Permissible  Grades.  For  a  general  discussion  of  the 
subject  of  maximum  and  minimum  grades,  see  §  76-86;  and  for 
examples  of  maximum  grades  for  broken-stone  roads,  see  §  82-85. 

325.  PREPARING  THE  SUBGRADE.  The  broken  stone  is  de- 
signed to  take  the  wear  of  hoofs  and  wheels,  but  the  earth  founda- 
tion must  support  the  load,  and  therefore  any  road  which  is  con- 
structed without  giving  due  attention  to  the  earth  road-bed  is 
wrong  from  the  start,  and  will  never  be  a  good  road  until  the  defect 
is  remedied. 

For  instructions  concerning  the  construction  of  embankments 
and  excavations,  see  §  119-22.  In  building  an  embankment 
upon  which  broken  stone  is  to  be  laid,  every  reasonable  care  should 
be  taken  to  prevent  uneven  settlement.  It  is  sometimes  advisable 
to  delay  the  laying  of  macadam  for  at  least  a  year  in  order  to  give 
the  embankment  time  to  settle,  for  it  is  impossible  to  construct  an 
embankment  of  earth  more  than  a  few  feet  in  height  without  hav- 
ing subsequent  settlement.  If  this  settling  took  place  evenly  all 
along  the  embankment,  no  particular  harm  would  be  done  to  the 


*  Rockwell's  Roads  and  Pavements  in  France,  p.  52— from  Monsieur  A.  Debauve, 
Ingenieur  en  chef  des  Ponts  et  Chaussces. 


212  BROKEN-STONE    ROADS.  [CHAP.   V. 

macadam  laid  upon  it;  but  owing  to  the  difference  in  the  soils  com- 
posing embankments,  and  also  in  the  way  the  earth  is  dumped, 
there  is  always  a  tendency  for  some  parts  to  settle  more  than  others. 
Sometimes  the  road  surface  is  placed  so  low  that  it  forms  a 
gutter  to  drain  the  adjacent  fields,  which  of  course  is  very  objec- 
tionable. Occasionally  the  earth  from  the  side  ditches  and  from 
the  trench  in  which  the  stone  is  placed,  is  deposited  at  the  side 
of  the  right-of-way  instead  of  being  used  to  raise  the  road  surface. 
In  this  connection,  see  §  126. 

326.  After  the  subgrade  has  been  brought  to  the  proper  form 
(§  305),  it  should  be  rolled  thoroughly — both  to  consolidate  it 
and  to  discover  soft  spots.  For  a  discussion  of  road  rollers,  see 
§  336-40. 

In  rolling,  quicksand  spots  are  sometimes  discovered,  in  which 
case  the  troublesome  material  should  be  excavated  and  suitable 
material  be  substituted.  If  the  road-bed  be  of  sand  or  of  material 
of  such  a  nature  as  to  push  along  in  a  wave  in  front  of  the  roller,  a 
thin  layer  of  broken  stone  or  gravel  strewn  over  the  surface  will 
enable  the  roller  to  consolidate  the  road-bed.  If  the  surface  is 
clay  that  sticks  to  the  roller,  sprinkle  a  thin  layer  of  sand  or  cinders 
over  the  surface. 

327.  SETTING  THE  TELFORD.  The  distinguishing  feature  of 
a  telford  road  is  its  paved  foundation.  After  the  road-bed  has  been 
brought  to  the  proper  form  and  been  rolled,  rough  stones  are  set 
upon  the  surface  to  form  a  pavement  5  to  8  inches  thick,  the 
thickness  depending  upon  that  to  be  given  to  the  finished  road 
(§  318),  the  general  practice  being  to  make  the  paved  foundation 
about  two  thirds  of  the  total  thickness  of  the  road.  The  practice 
of  Telford  was  to  grade  the  road-bed  flat,  and  then  construct  his 
pavement  deeper  in  the  middle  than  at  the  sides,  using  for  a  road- 
way 16  feet  wide,  stones  about  8  inches  deep  at  the  middle  and  5 
inches  at  the  sides.  This  practice  is  still  followed  by  some  engi- 
neers, but  it  is  now  more  common  and  usually  considered  preferable 
to  make  the  surface  of  the  road-bed  parallel  to  the  finished  surface 
and  the  pavement  of  uniform  thickness.  Fig.  45,  page  198,  shows 
a  telford  road  with  a  level  subgrade;  and  Fig.  46,  page  198,  a  tel- 
ford road  with  the  subgrade  parallel  to  the  finished  surface. 

The  size  of  the  stones  for  the  telford  pavement  is  of  no  great 


ART.   2.]  CONSTRUCTION".  213 

importance,  at  least  there  is  a  great  difference  in  the  practice  of  the 
best  road  builders.  The  width  of  these  stones  varies  from  3  to  10 
inches,  3  to  6  being  most  common;  and  the  length  varies  from  6 
to  20  inches,  8  to  12  being  most  common.  It  is  desirable  to  have 
the  width  on  any  particular  job  somewhat  nearly  uniform,  and  the 
stones  in  any  course  should  be  still  more  nearly  equal.  The  stones 
are  set  upon  their  widest  edge  with  their  greatest  length  across  the 
road,  the  joints  being  broken  as  much  as  possible.  Each  stone 
should  stand  independently  of  its  neighbor,  i.  ev  one  stone  should 
not  lean  against  another.  The  irregularities  of  the  upper  surface 
are  then  broken  off  with  a  hammer,  and  the  interstices  between 
the  stones  are  filled  with  spalls  lightly  driven  into  place  with  a  ham- 
mer or  a  crow-bar.  This  knocking  off  of  the  projecting  points  and 
the  driving  of  spalls  into  the  interstices  should  not  be  'done  so  near 
the  face  of  the  pavement  as  to  dislocate  the  stones  last  set.  It  is 
frequently  specified  that  no  wedging  shall  be  done  within  10  or  15 
feet  of  the  front  edge  of  the  pavement.  After  the  projecting 
points  have  been  knocked  off  and  the  interstices  have  been  filled 
with  stone  chips  or  ordinary  crushed  stone,  the  pavement  is  usually 
rolled.  It  is  usually  specified  that  the  roller  shall  not  go  nearer 
to  the  front  of  the  pavement  than  25  to  30  feet. 

The  cardinal  requisite  of  a  telford  foundation  is  the  interlocking 
of  the  stone  closely  and  compactly  together  by  barring,  wedging, 
and  rolling  until  the  entire  structure  is  brought  in  action  to  resist 
disturbance  as  a  single  mass. 

328.  CRUSHING  THE  STONE.  The  introduction  of  a  machine 
for  breaking  the  material  greatly  cheapened  the  cost  of  broken- 
stone  roads.  The  rock  crusher  was  introduced  into  America  in 
1860,  before  which  time  the  stone  was  broken  by  hand  with  ham- 
mers on  the  side  of  the  road.  Coincident  with  the  introduction 
of  power  for  breaking  the  stone,  came  the  revolving  screen  which 
permitted  the  fragments  to  be  assorted  as  to  size — an  important 
feature,  as  we  shall  soon  see. 

Formerly  there  was  much  discussion  as  to  the  relative  merits 
of  hand-  and  machine-broken  stone;  but  the  difference  in  value 
is  so  slight  and  the  difference  in  cost,  particularly  in  this  country, 
is  so  great  that  the  question  has  been  answered  practically  in  favor 
of  the  machine-broken  stone. 


214 


BROKEN-STOXE    ROADS. 


[CHAP. 


329.  Forms  of  Crushers.  There  are  two  types  of  crushers  now 
in  common  use.  The  older  one,  often  called  the  Blake  after  the 
original  inventor,  consists  of  a  strong  iron  frame,  near  one  end  of 
which  is  a  movable  jaw.  By  means  of  a  toggle-joint  and  an  eccen- 
tric, this  jaw  is  moved  backward  and  forward  a  slight  distance.  As 
the  jaw  recedes  the  opening  increases  and  the  stone  descends;  as  the 
jaw  again  approaches  the  frame,  the  stone  is  crushed.  The  maximum 
size  of  the  product  is  determined  by  the  distance  the  jaw  platen 
are  from  each  other  at  their  lower  edge.  This  machine  is  also  fre- 
quently called  the  oscillating  breaker, or  jaw  breaker.  Fig.  59  shows 


Fig.  59.— Oscillatory   Stone  Crushkr. 

one  form  of  this  type.  The  size  of  the  product  is  regulated  by 
raising  or  lowering  the  wedge  10,  Fig.  59,  or  by  inserting  a  differ- 
ent pair  of  toggles, — 7,  Fig.  59. 

The  second  form  of  crusher,  called  the  Gates  after  the  original 
inventor,  consists  of  a  solid  conical  iron  shaft  which  is  supported 
within  a  heavy  iron  mass  shaped  somewhat  like  an  inverted 
bell.  By  means  of  an  eccentric  shaft  a  rocking  and  rotary  motion 
is  given  to  the  shaft,  so  that  each  point  of  its  surface  is  successively 
brought  near  to  and  removed  from  the  surface  of  the  bell,  which 
causes  the  stone  to  be  successively  crushed  as  it  descends.     Fig.  60 


ART.   2.] 


CONSTRUCTION. 


215 


shows  one  form  of  this  type  of  crusher.  An  adjustment  permits  a 
variation  in  the  size  of  the  product.  This  form  is  often  called  the 
rotary  breaker  or  gyratory  breaker. 

The  gyratory  crusher  has  one  advantage  over  the  oscillatory 
form.  The  latter  breaks  the  stone  and  then  draws  back,  the  stone 
dropping  down  ready  to  receive  the  thrust  of  the  jaw  when  it  is 
next  pushed  forward;  and  thus  time  is  lost  while  the  jaw  is  reced- 


Fig.  60.— Gyratory  Rock  Crusher. 

mg,  and  more  power  is  required  to  start  without  momentum 
against  the  stone.  With  the  gyratory  crusher  no  time  is  lost  in  gath- 
ering for  a  new  stroke,  and  the  power  is  uniform  and  continuous. 
Both  machines  are  driven  by  steam  or  occasionally  by  horse- 
power. Both  are  made  in  a  great  variety  of  sizes,  capable  of 
crushing  from  10  to  200  tons  per  day.     There  are  many  conflicting 


216 


BROKEN- STONE  ROADS. 


[CHAP.  V. 


claims  as  to  the  relative  merits  of  the  two  types,  but  both  are  very 
excellent  machines.  In  determining  the  relative  economic  effi- 
ciency, it  is  necessary  to  consider  the  output,  the  power  required, 
the  cost  of  repairs,  the  expense  of  moving  the  machine  from  point 
to  point,  the  amount  of  sledging  required,  etc. 

330.  Arrangement  of  Plant.  More  important  than  the  econom- 
ical working  of  the  machine,  is  the  general  arrangement  of  the  entire 
plant  for  handling  and  crushing  the  stone.  The  plant  should  be 
arranged,  if  at  all  possible,  so  that  the  stone  may  be  delivered 
from  the  quarry  or  from  the  field  on  a  level  with  the  mouth  of  the 
crusher,  and  thus  save  lifting  the  entire  product  by  hand  in  throw- 
ing it  into  the  machine.  The  crushed  stone  should  be  elevated 
to  bins  or  pockets,  one  for  each  size,  so  arranged  as  to  discharge 
directly  into  the  wagons  or  carts  that  haul  it  to  the  road — see  Fig. 
61.    The  bins  should  have  a  considerable  capacity,  so  as  to  prevent 


Fia.  61.— Arrangement  of  Stone-crushing  Plant. 

stoppage  of  the  machine  if  the  roads  are  too  bad  to  haul  or  if  for  any 
other  reason  the  removal  of  the  crushed  stone  is  delayed.  There 
should  be  ample  room  about  the  plant  to  prevent  the  interference 
of  the  teams  in  going  and  coming.    To  secure  all  of  these  conditions 


ART.  2.]  CONSTRUCTION.  217 

requires  a  careful  study  of  the  problem,  and  a  proper  adjustment 
of  them  is  a  matter  greatly  affecting  the  cost  of  the  product.  In 
permanent  plants  these  conditions  are  very  carefully  attended  to; 
but  in  temporary  outfits  it  is  not  always  possible  to  secure  an  ideal 
adjustment.  '  In  many  cases  the  arrangement  could  be  greatly 
improved  at  comparatively  little  expense. 

A  well  arranged  stone-crushing  plant  costs  from  $1,500  to  $2,500, 
the  cost  of  an  average  plant  being  divided  about  as  follows :  a9"X 
15"  crusher,  $700;  a  rotary  screen  and  elevator,  $300;  engine  and 
boiler,  $600;  portable  bins,  $300;  miscellaneous  fittings,  $100; 
total  $2,000.     For  data  on  the  cost  of  crushing  stone,  see  §  353. 

331.  SIZES  OF  STONE.  The  size  of  stone  used  for  road  metal 
depends  upon  the  hardness  and  toughness  of  the  stone  and  upon 
the  weight  of  the  traffic.  The  harder  and  tougher  the  material, 
the  smaller  it  may  be  broken  without  danger  of  its  crushing  or  shat- 
tering under  the  load  of  wheels  and  the  impact  of  hoofs;  and  the 
harder  and  tougher  a  stone,  the  smaller  it  must  be  broken  in  order 
that  it  may  compact  well  in  the  road.  The  stones  in  the  top  course 
should  be  larger  for  heavy  traffic  than  for  light  traffic,  to  prevent 
their  being  ground  to  powder.  Larger  stones  can  be  used  in  the 
bottom  layers  of  a  road  than  at  the  top. 

One  of  MacAdam's  rules  was  to  exclude  any  fragment  weighing 
more  than  6  ounces.  Telford's  limit  was  8  ounces.  A  1^-inch 
cube  of  compact  limestone  weighs  about  6  ounces.  Another  of 
MacAdam's  rules  was  to  exclude  any  stone  that  could  not  readily 
be  put  into  a  man's  mouth.  These  rules  are  frequently  quoted, 
even  now,  although  improvements  in  road  machinery  have  made 
them  inappropriate  with  present  methods.  When  these  rules  were 
established,  the  road  was  not  rolled  but  was  compacted  by  traffic; 
and  as  the  stone  was  broken  by  hand  little  or  no  fine  material  was 
produced,  and  hence  the  road  was  bound  chiefly  by  manure  and  dirt 
brought  on  by  the  traffic.  Rolling  and  the  use  of  stone  dust  for  a 
binder  make  a  material  difference  in  the  sizes  of  the  stone  per- 
missible. 

The  bottom  course  of  a  macadam  road  built  of  soft  stones  is 
often  composed  of  fragments  3  to  4  inches  in  greatest  dimensions; 
but  if  it  is  built  of  hard  tough  stone,  the  sizes  are  2  to  2£  inches. 
The  size  of  rock  in  the  lower  courses  is  not  so  important  as  that  for 


218  BROKEN-STONE   ROADS.  [CHAP.   V. 

the  surface  course  (see  §  332).  The  top  course  of  hard  tough  stones 
is  usually  1  to  2  inches  for  heavy  traffic,  and  J  to  1  inch  for  light 
traffic.  It  is  often  claimed  that  a  smooth  road  can  not  be  built 
with  stones  2  inches  in  diameter;  but  with  sufficient  rolling  and  a 
good  binding  material,  a  comparatively  smooth  road  may  be  se- 
cured with  such  stones,  and  the  road  will  last  much  longer  than 
one  built  of  finer  material. 

The  custom  is  to  lay  the  stone  in  courses  of  substantially  one 
size,  although  some  road  builders  prefer  to  have  the  sizes  mixed 
when  thrown  into  the  road.  The  only  advantage  of  the  latter 
practice  is  that  with  a  skilful  proportioning  of  the  sizes  less  rolling 
is  required;  but  it  is  objectionable  owing  to  the  difficulty  of  getting 
the  several  sizes  properly  proportioned  and  keeping  them  thor- 
oughly mixed.  There  is  generally  too  much  fine  material  in  the 
mixed  sizes,  which  makes  the  road  wear  rapidly  and  unevenly. 

Connected  with  the  crusher  and  run  with  the  same  power  is 
generally  a  rotary  screen  having  meshes  of  three  sizes — usually 
about  \,  \\,  and  2\  inches.  Fig.  61,  page  216,  shows  a  common 
arrangement  of  crusher,  elevator,  screen,  and  bins. 

332.  For  economic  reasons  the  size  of  stone  in  the  several 
courses  arid  their  thickness  should  be  adjusted  so  as  to  use,  if  possi- 
ble, all  of  the  output  of  the  crusher.  The  output  of  the  various 
sizes  varies  considerably  with  the  character  of  the  stone.  With  a 
hard  stone,  half  or  more  *of  the  product  of  the  crusher  will  not  pass 
through  the  ^~mch  screen;  while  with  field  stones  one  half  may 
pass  through  such  a  screen.  The  last  gives  more  "  fines  "  or  "  screen- 
ings" than  can  be  used  profitably  during  construction,  but  the 
surplus  is  very  useful  in  maintaining  the  surface.  With  some  rocks 
it  is  difficult  to  get  enough  fine  material  for  use  in  the  original  con- 
struction. 

333.  SPREADING  THE  STONE.  The  stone  is  usually  hauled 
from  the  crusher  to  the  road  in  wagons  or  carts,  dumped  upon  the 
roadway,  and  spread  by  forks  or  rakes.  This  practice  is  objec- 
tionable, since  the  coarse  and  fine  fragments  become  separated  in 
the  process,  producing  a  layer  of  unequal  density  and  an  irregular 
surface  after  rolling.  It  is  sometimes  specified  that  the  stone  shall 
be  dumped  upon  a  plank  platform,  from  which  it  is  distributed 
with  shovels.     This  last  method  of  spreading  costs  4  to  6  cents 


ART.  2.]  CONSTRUCTION.  219 

per  cubic  yard — about  twice  that  by  dumping  and  raking  (see 
§  356) — and  is  appropriate  only  when  the  very  best  results  are 
sought.  Wagons  are  upon  the  market  which  automatically  dump 
and  distribute  the  stone  in  layers  of  uniform  thickness,  but  owing 
to  their  cost  and  weight  they  are  not  in  very  general  use.  Some 
contractors  use  a  road  leveler  to  distribute  the  broken  stone,  for 
which  purpose    the    Shuart    grader,  Fig.  62,  has   some  marked 


Fig.  62.— Shuart  Grader. 

advantages.  The  blade  can  be  set  at  any  angle  with  the  line  of 
draft,  and  is  adjustable  in  height.  The  guards  at  the  ends  of  the 
blade  can  be  swung  entirely  out  of  the  way,  and  then  the  machine 
may  be  used  to  level  or  crown  the  subgrade. 

The  stone  should  be  applied  in  uniform  layers,  the  thickness 
of  each  depending  upon  the  total  thickness  of  the  road.  Two 
methods  are  in  use  for  gaging  the  thickness  of  the  layers  of  stone. 
1.  On  the  finished  subgrade,  wood  cubes  of  a  depth  equal  to  the 
thickness  of  the  layer  are  set  at  frequent  intervals,  and  the  loose 
stone  is  laid  even  with  the  tops  of  these  blocks.  This  method  is 
sometimes  described  as  building  by  blocks,  and  is  the  one  em- 
ployed on  the  state- aid  roads  of  New  Jersey.  2.  The  soil  is  brought 
to  an  established  grade,  and  the  finished  road  is  required  to  be 
brought  to  another  established  grade,  in  which  case  neither  the 
absolute  thickness  nor  the  uniformity  of  the  several  courses  is  a 


220  BROKEN-STONE    ROADS.  [CHAP.   V. 

matter  of  much  importance.  This  method  is  employed  on  the 
state-aid  roads  in  Massachusetts. 

334.  SHRINKAGE  IN  ROLLING.  Before  beginning  to  spread  the 
layers  of  stone,  it  is  necessary  to  inquire  as  to  the  amount  the 
crushed  stone  will  shrink  in  rolling.  The  shrinkage  has  an  impor- 
tant bearing  upon  the  thickness  and  cost  of  the  finished  road ;  but 
the  amount  of  shrinkage  is  often  greatly  over-estimated.  It  is  fre- 
quently stated  that  rolling  will  cause  broken  stone  to  shrink  33 
per  cent;  or,  as  it  is  usually  put,  6  inches  will  roll  down  to  4.  Ap- 
parently this  statement  is  based  upon  MacAdam's  experience;  but 
MacAdam  used  neither  a  binding  material  nor  a  roller,  and  the 
road  was  compacted  only  after  months  of  travel,  when  the  traffic 
had  pulverized  sufficient  material  to  bind  the  road  and  after  much 
of  that  which  had  been  pulverized  had  blown  away.  The  follow- 
ing examples  from  actual  practice  show  no  such  shrinkage. 

In  one  case,*  with  trap  rock  1 J  to  2\  inches,  rolled  with  a  124- 
ton  steam  roller  upon  a  subgrade  so  hard  that  the  wagons  hauling 
the  stone  made  no  ruts,  5.67  inches  of  loose  stone  rolled  to  4  inches, 
and  7.38  inches  rolled  to  6  inches.  The  average  thickness  of  the 
loose  stone  was  determined  by  dividing  the  quantity  of  stone  rrsed 
by  the  area  covered.  The  first  is  a  shrinkage  of  29  per  cent  and 
the  second  of  19  per  cent.  The  difference  between  these  two  re- 
sults is  probably  due  to  errors  of  observation,  to  variations  in  the 
thickness  of  the  finished  road,  and  to  the  fact  that  the  thicker 
layers  did  not  compact  as  solidly  as  the  thinner  ones.  The  stone 
was  rolled  dry  until  the  desired  thickness  was  reached,  when  the 
binder  was  added,  and  sprinkling  was  commenced. 

In  another  case,f  with  2-inch  trap  laid  on  the  compact  surface 
of  an  old  crushed-stone  road  and  rolled  with  a  12-ton  roller,  3.9 
inches  of  loose  stone  rolled  to  3  inches.  The  shrinkage  was  23  per 
cent.  The  thickness  was  determined  from  the  area  covered  and 
the  quantity  of  stone  used.  No  stone  could  have  been  forced  into 
the  subgrade,  but  there  was  some  uncertainty  as  to  the  average 
elevation  of  the  surface  of  the  old  street. 

It  has  been  determined  \  by  tests  over  several  miles  of  road 

*W.  C.  Foster  in  Trans.  Amer.  Soc.  of  Civil  Eng'rs,  Vol.  41,  p.  135-38. 

f  F.  G.  Cudworth  in  Trans.  Amer.  Soc.  of  Civil  Eog'rs,  Vol.  41,  p.  126-28. 

\  H.  P.  Gillette  in  Economics  of  Road  Construction,  p.  19-20.    New  York,  1901. 


ART.   2.]  CONSTRUCTION.  221 

where  the  output  of  the  crusher  was  carefully  measured  in  wagons 
and  also  when  rolled  in  place,  that  6  inches  of  loose  hard  limestone 
will  roll  down  to  4}  inches,  which  is  a  shrinkage  of  20  per  cent. 

335.  It  is  probable  that  the  maximum  actual  shrinkage  in  roll- 
ing  is  less  than  20  per  cent.  The  apparent  shrinkage  depends  upon 
the  nature  and  condition  of  the  subgrade,  i.  e.,  upon  the  amount 
of  stone  forced  into  the  earth. 

If  the  soil  is  clay,  the  sprinkling  required  to  work  the  binder 
into  the  interstices  may  soften  the  subgrade  so  that  considerable 
stone  will  be  forced  into  the  earth.  This  condition  is  indicated  by 
the  roller's  leaving  tracks  upon  the  surface;  and  when  this  occurs, the 
work  should  be  stopped  until  the  subgrade  dries  out.  To  prevent 
the  crushed  stone  from  being  forced  into  the  clay  subgrade  during 
construction  or  after  completion — particularly  when  the  frost  is 
going  out, — a  layer  of  sand,  stone  screenings,  ashes^  or  the  like, 
is  sometimes  interposed.  The  English  engineers  often  use  "  hard 
core  "  (a  mixture  of  brick  rubbish,  old  plastering,  and  broken  stone) 
on  a  clay  soil,  to  prevent  the  mud's  working  into  the  metaling.  Any 
material  not  affected  by  water  is  useful  for  this  purpose ;  and  the 
finer  it  is  the  better,  since  the  smaller  will  be  the  apertures  in  it, 
and  the  more  certainly  will  it  prevent  the  soil  from  coming  up 
through  it. 

If  the  soil  is  sandy,  a  thin  layer  of  coarse  gravel  or  broken  stone 
laid  upon  the  surface  and  then  rolled,  will  prevent  any  further  loss 
of  the  road  metal  in  the  subgrade.  If  the  soil  is  nearly  pure  sand, 
the  wetter  it  is  the  less  crushed  stone  will  be  forced  into  it;  and 
therefore  if  water  is  plentiful,  it  may  be  wise  to  keep  the  sand  satu- 
rated while  the  rolling  is  in  progress  to  prevent  the  loss  of  the  stone. 
The  Massachusetts  Highway  Commission  used  cotton  cheese-cloth 
on  a  soft  fine  sand  to  prevent  the  stone  from  sinking  into  the  sub- 
grade.  "  It  is  not  at  all  needful  that  the  partition  should  be  endur- 
ing, for  as  soon  as  the  stones  in  the  lower  layer  have  been  forced 
into  contact  and  have  become  bound  together,  there  is  no  further 
danger  of  the  mingling  of  the  stone  with  the  sand;  and  hence  the 
speedy  decay  of  the  fabric  is  a  matter  of  no  consequence.  The  cloth 
was  spread  in  strips  lengthwise  of  the  way;  and  the  stone  for  the 
bottom  layer  was  shoveled  from  the  sides  upon  it  with  no  unusual 
care.     A  section  through  such  a  road  shows  that  the  stones  do  not 


222  BROKEN-STONE   ROADS.  [CHAP.  V. 

tear  through  the  cloth.  At  3  cents  per  square  yard  on  the  road, 
the  cost  of  the  cloth  may  be  less  than  one  third  that  due  to  the 
loss  of  the  broken  stone  which  would  occur  if  it  were  allowed  to  come 
directly  in  contact  with  the  sand.  Various  kinds  of  strong  paper 
were  tried,  but  found  worthless."  *  "A  thick  coating  of  straw  has 
been  used  to  hold  up  the  macadam  on  a  sandy  soil."t 

However,  if  the  sand  is  firm  enough  to  hold  up  the  stone  during 
the  rolling,  it  is  not  necessary  to  prevent  the  mixing  of  the  sand 
and  the  stone,  since  the  subgrade  may  be  left  a  little  high,  with 
the  expectation  of  forcing  the  stone  into  the  sand.  This  is  equiv- 
alent to  using  the  sand  of  the  subgrade  as  a  filler  or  binder  for  the 
lower  portion  of  the  broken  stone.  If  the  sand  is  dry  and  nearly 
pure,  it  can  be  thus  forced  nearly  to  the  top  of  a  4-inch  course  of 
coarse  broken  stone. 

336.  ROLLERS.  The  roller  is  indispensable  for  the  economic 
construction  of  broken-stone  roads.  Roads  can  be  built  without 
the  use  of  a  roller,  but  always  at  large  expense  to  the  traffic  and  with 
great  waste  of  the  road  metal;  and  such  roads  never  have  as  smooth 
a  surface  and  are  not  as  durable  as  if  a  roller  had  been  employed 
in  their  construction.  With  traffic-consolidated  roads,  much  of 
the  metal  is  worn  round  and  smooth  before  the  fragments  become 
firmly  fixed  in  place;  and  the  dirt  brought  upon  the  road  by  the 
traffic  mixes  with  the  stone  and  prevents  it  from  ever  packing  as 
solidly  as  the  clean  stone  would,  and,  besides,  the  dirt  when  wet 
has  a  lubricating  effect  upon  the  stone  which  under  the  action  of 
traffic  causes  the  surface  to  break  up  readily.  Further,  during 
the  time  traffic  is  consolidating  the  stone,  the  surface  is  not  even 
approximately  water  tight;  and  therefore  the  subgrade  is  soft- 
ened by  rains,  and  the  stone  is  mixed  with  the  earth  below  and  vir- 
tually lost.  Ordinarily,  it  is  true  economy  to  compact  the  road 
by  the  use  of  a  roller. 

Classified  according  to  the  power  employed,  there  are  two 
forms  of  rollers :  the  horse  roller,  and  the  steam  roller.  The  horse 
roller  was  first  introduced  in  France  about  1834,  and  the  steam 
roller  in  1865.  Neither  Mac  Adam  nor  Telford  used  a  roller  ii\ 
constructing  roads,  as  it  was  invented  after  their  time. 

*  Shaler's  American  Highways,  p.  154-56. 

t  Gillette's  Economics  of  Road  Construction,  p.  12. 


ART.  2.] 


CONSTRUCTION. 


223 


337.  Horse  Rollers.     There  is  a  variety  of  horse  rollers  on  the 
market.     Fig.  63  shows  the  general  form.     Each  consists  essen- 


Fig.  63.— Reversible  Horse  Road  Roller. 

tially  of  a  hollow  cast-iron  cylinder  4  to  5  feet  long,  5  to  6  feet 
in  diameter,  and  weighing  from  3  to  6  tons.  Some  forms  are  pro- 
vided with  boxes  in  which  stone  or  iron  may  be  placed  to  in- 
crease the  weight,  and  some  have  closed  ends  and  may  be  filled 
with  water  or  sand.  Most  makers  provide  a  scraper  for  keeping 
the  roller  clean,  and  also  a  brake  for  controlling  the  motion  on  a 
down  grade.  In  the  better  forms,  the  direction  of  the  motion  is 
reversed  simply  by  swinging  the  tongue  around  the  machine.  The 
lighter  rollers  are  drawn  by  two  horses  and  the  heavier  by  four. 
The  weight  per  linear  inch  of  face  varies  from  200  to  300  pounds. 

The  catalogue  price  of  horse  rollers  is  usually  about  $100  per  ton. 

338.  Steam  Rollers.  There  are  two  type  forms  of  steam  rollers, 
as  shown  in  Fig.  64  and  65,  pages  224-25.  The  first  is  the  form  com- 
monly used  in  constructing  broken-stone  roads,  and  is  usually 
called  simply  a  steam  roller.  The  second  is  the  form  employed 
in  rolling  nsphalt  pavements,  and  is  often  called  an  asphalt  roller, 
and  also  a  Lindelof  roller — after  the  original  inventor. 

The  steam  stone-road  roller,  Fig.  64,  is  made  by  a  number  of 
manufacturers,  but  all  are  practically  the  same.     The  total  weight 


224 


BROKEN-STONE    ROADS. 


[CHAP.  V. 


varies  from  10  to  20  tons,  and  the  pressure  under  the  drivers  varies 
from  450  to  650  pounds  per  linear  inch.  The  cost  of  these  rollers 
is  usually  about  $200  to  $225  per  ton. 


Fig.  64.— Sieam  Stone-road  Roller. 

There  has  recently  been  introduced  a  type  of  traction  engine, 
the  wheels  of  which  may  be  replaced  by  heavy  rollers,  thus  con- 
verting the  traction  engine  into  a  road  roller  of  moderate  weight. 
The  rolls  cost  $200  to  $300  in  addition  to  the  price  of  the  engine. 
A  machine  of  this  kind  would  be  valuable  as  a  substitute  for  a  road 
roller  where  the  amount  of  work  will  not  justify  the  purchase  of  a 
steam  roller  and  where  the  traction  engine  could  be  employed  part 
of  the  time  for  other  purposes. 

The  asphalt  roller.  Fig.  65,  page  225,  differs  from  the  preceding 
form  chiefly  in  being  lighter  and  in  being  so  arranged  that  the  front 
and  rear  rolls  cover  the  same  space.  The  rear  roller  may  be  filled 
with  water  or  sand.  The  main  purpose  of  this  roller  is  to  smooth 
rather  than  to  compress,  but  it  can  be  used  for  stone- road  con- 
struction. The  weight  varies  from  3  to  15  tons.  5  tons  being  the 
usual  weight.     The  pressure  under  the  front  roll  is  usually  about 


ART.  2.] 


CONSTRUCTION. 


225 


200  pounds  per  linear  inch  of  face,  and  that  under  the  rear  roll  can 
be  varied  between  200  to  260  pounds  per  linear  inch  of  face. 

339.  It  is  desirable  that  the  weight  of  the  roller  should  be  pro- 
portional to  the  hardness  of  the  stone,  as  toe  great  a  weight  crushes 
the  material  instead  of  compacting  it.  An  excessively  heavy  roller 
will  sometimes  sink  into  light  or  loose  soil,  and  force  it  ahead  in  a 
wave  which  the  roller  can  not  surmount.    This  may  sometimes 


Fro.  65.— Asphalt  Roller. 


be  prevented  by  spreading  a  thin  layer  of  sand  or  gravel  on  the 
surface  being  rolled.  A  similar  difficulty  sometimes  occurs  with  a 
heavy  roller  on  a  layer  of  loose  stones.  If  the  front  wheels  or 
rollers  of  the  machine  were  larger,  this  difficulty  would  be  de- 
creased. In  localities  where  the  soil  is  of  a  loose  sandy  nature,  a 
roller  weighing  10  or  12  tons  is  usually  preferred;  and  in  districts 
where  the  soil  is  gravelly  or  stiff  clay,  a  weight  of  12  or  15  tons  is 
used.  In  localities  where  the  road  material  is  hard,  a  15-ton  roller 
is  necessary;  but  with  the  softer  stones  a  weight  of  10  or  12  tons 
is  sufficient. 

340.  Horse  vs.  Steam  Rollers.  There  was  once  considerable 
discussion  as  to  the  relative  merits  of  the  horse  and  the  steam  roller, 
but  it  is  now  settled  that  a  steam  rolJer  is  indispensable  for  the 
construction  of  the  best  stone  roads.  The  horse  roller  is  the  cheaper 
in  first  cost,  is  lighter,  and  is  generally  cheaper  to  operate;  but 
on  account  of  its  lighter  weight  it  is  less  effective  on  soft  material 


226  BB0KEX-ST0NE    EOADS.  [CHAP.   V. 

than  the  steam  roller,  and  can  not  thoroughly  compact  the  harder 
road  materials,  and,  besides,  the  horses'  feet  often  loosen  the 
material  nearly  as  fast  as  it  is  packed  down  by  the  roller.  The 
time  required  to  consolidate  a  stone  road  varies  with  the  weight 
of  the  roller,  and  for  this  reason  roads  can  be  built  more  quickly 
with  the  steam  than  with  the  horse  roller. 

For  compacting  the  subgrade  of  roads  and  pavements,  the  horse 
roller  is  reasonably  effective.  However,  there  is  one  important  ad- 
vantage in  using  the  steam  roller  to  consolidate  the  subgrade  of  a 
street  pavement:  One  of  the  chief  objects  in  rolling  the  foundation 
is  to  discover  partially  filled  trenches,  which  usually  run  both 
lengthwise  and  crosswise  of  the  street;  and  therefore  the  roller 
should  be  run  over  the  street  both  longitudinally  and  transversely. 
The  latter  can  be  done  only  with  a  steam  roller. 

341.  ROLLING  THE  STONE.  Rolling  is  a  very  important  part 
of  the  construction  of  a  broken-stone  road.  The  subgrade  should 
be  rolled  to  prevent  the  stone  from  being  forced  into  the  earth. 
The  lower  course  of  the  stone  should  be  rolled  to  compact  it,  so 
that  the  pieces  will  not  move  one  upon  the  other  under  the  traffic; 
and  the  top  course  should  be  rolled  to  pack  or  bind  the  pieces  into 
place,  to  prevent  their  being  knocked  out  by  the  horses'  feet.  Roll- 
ing accompanied  by  sprinkling  is  necessary  also  to  work  the  bind- 
ing material  into  the  interstices  so  as  to  make  the  surface  water- 
tight. Roads  that  have  been  consolidated  by  traffic  are  largely 
held  together  by  mud,  and  after  long  use  are  fairly  smooth  and 
hard  in  dry  weather,  but  soon  become  soft  and  muddy  during  a 
wet  time. 

The  stone  is  put  on  in  two  or  three  layers, — according  to  the 
total  thickness  of  the  finished  road, — and  each  course  is  thoroughly 
rolled  before  the  next  is  added.  The  courses  should  not  be  more 
than  4  to  6  inches  thick.  When  a  telford  foundation  is  used,  broken 
stone  is  spread  over  the  pavement  to  bring  the  top  surface  to  the 
proper  form  and  height,  after  which  it  is  rolled. 

342.  The  rolling  should  proceed  gradually  from  both  sides  tow- 
ard the  center.  If  the  weight  of  the  roller  can  be  varied,  com- 
mence with  the  unballasted  roller,  and  increase  the  weight  as  the 
stone  becomes  consolidated.  If  the  surface  of  the  layer  shows  a 
wavy  motion  after  being  rolled  three  or  four  times,  the  subgrade 


ART.   2.]  CONSTRUCTION".  227 

is  too  wet,  and  time  should  be  given  it  to  dry  out.  Some  coarse 
brittle  granitic  rocks  begin  to  crawl  and  the  sharp  edges  to  break 
off  after  the  roller  has  passed  over  them  a  few  times ;  but  a  light 
sprinkling  of  sand  or  stone  screenings  will  prevent  this,  and  fa- 
cilitate the  consolidation  of  the  layer.  All  irregularities  of  the 
surface  developed  by  the  rolling  should  be  corrected  by  filling  the 
depressions  with  stone  of  the  size  used  in  the  layer. 

The  rolling  should  be  continued  until  the  stone  ceases  to  creep 
in  front  of  the  roller,  and  until  the  macadam  is  firm  under  the  foot 
as  one  walks  over  it.  When  the  rolling  is  complete,  one  of  the 
larger  stones  of  the  course  can  be  crushed  under  the  roller  without 
indenting  the  surface  of  the  layer. 

When  the  first  course  has  been  consolidated,  a  second,  usually 
a  thinner  one  of  smaller  stones,  is  added,  and  then  rolled  the  same 
as  the  first.  Finally  a  third  course  consisting  of  about  half  an  inch 
of  sand  or  fine  stone  and  stone  dust  is  added.  The  roller  is  then 
passed  over  this  layer,  with  the  result  that  the  bits  are  ground  to 
powder.  As  the  rolling  of  this  course  proceeds  it  is  sprinkled, 
the  aim  of  the  sprinkling  and  rolling  being  to  work  the  fine  material 
into  the  cavities  between  the  pieces  of  crushed  stone,  thus  binding 
the  whole  into  a  solid  mass.  The  proper  binding  of  the  road  is  the 
irk»»#%TLportant  part  of  the  construction,  and  will  be  more  fully 
considered  presently  (see  §  345). 

343.  Amount  of  Rolling.  The  total  amount  of  rolling  re- 
quired varies  with  the  weight  of  the  roller,  the  hardness  and  the 
sice  of  the  stone,  and  the  amount  of  binder  and  water  used.  Trap 
rock  being  very  hard  requires  two  or  three  times  as  much  rolling 
as  most  other  stone.  An  excess  of  binding  material  and  of  water 
gives  a  compact  surface  with  comparatively  little  rolling,  but  the 
road  is  not  as  durable  as  though  it  had  been  more  thoroughly 
rolled. 

In  New  York  City,  5  inches  of  crushed  gneiss  on  telford  and 
5  inches  of  trap  on  the  gneiss,  bound  with  trap  screenings,  was 
rolled  with  a  15-ton  steam  roller  at  the  rate  of  40.6  sq.  yd.  per  hour, 
or  10  cu.  yd.  per  hour.  Although  it  is  common  to  give  the  amount 
of  rolling  in  terms  of  the  time  required,  the  statement  is  somewhat 
indefinite,  since  the  work  accomplished  varies  with  the  speed  of 
the  roller  and  also  with  the  length  of  run,  i.  e.,  with  the  time  lost 


228  BROKEN-STOKE    ROADS.  [CHAP.   V. 

in  starting  and  stopping.  The  usual  speed  of  steam  rollers  is  2  to 
2£  miles  per  hour.  The  above  work  is  equivalent  to  0.553  ton- 
miles  per  sq.  yd.,  or  2.246  ton-miles  per  cubic  yard.  The  number 
of  trips  was  130.* 

In  making  repairs,  a  6-inch  course  of  2-inch  trap  was  rolled  at 
the  rate  of  26.2  sq.  yd.  per  hour,  or  4.4  cu.  yd.  per  hour.  The  work 
amounted  to  about  0.859  ton-miles  per  sq.  yd.,  or  5.177  ton-miles 
per  cu.  yd.     The  number  of  trips  over  the  surface  was  201. f 

An  area  of  22,000  square  yards  of  a  3-inch  course  of  2-inch  trap 
upon  an  old  broken-stone  road,  bound  with  trap-rock  screenings 
and  rolled  with  a  10-ton  steam  roller,  was  finished  at  an  average 
rate  of  47.15  sq.  yd.  per  hour  of  rolling,  the  extremes  being  38.4 
and  61.1  sq.  yd.  per  hour.  This  was  an  average  of  about  4.0  cu. 
yd.  per  hour.  J 

A  6-inch  course  of  \\  to  2J-inch  trap  rock,  bound  with  lime- 
stone screenings,  was  rolled  with  a  12^-ton  steam  roller  at  an  aver- 
age rate  of  31.4  sq.  yd.  per  hour,  or  5.2  cu.  yd.  per  hour.§ 

The  Hudson  County  Boulevard  (Jersey  City,  N.  J.)  consists 
of  8  inches  of  telford,  2\  inches  of  2£-inch  stone,  \\  inches  of  \\- 
inch  stone,  and  then  \  to  1  inch  of  coarse  screenings — all  trap  rock. 
The  macadam  top  was  supposed  to  roll  down  to  4  inches,  i.  e.,  4J 
to  5  inches  of  loose  stone  was  supposed  to  roll  to  4  inches.  The 
rolling  was  distributed  about  as  follows:  On  the  telford,  10  to  12 
passages;  on  the  2^-inch  course,  8  to  10  passages;  on  the  lj-inch 
course,  10  to  12;  and  on  the  screenings,  80  to  90, — making  a  total 
of  100  to  120  passages  of  the  roller  over  the  road. 

344.  The  above  examples  are  representative  of  American  prac- 
tice in  building  the  best  crushed-stone  roads,  and  represent  consid- 
erably more  rolling  than  is  customary  in  either  England  or  France. 
In  Paris  the  porphyry  roadways  with  courses  from  3  to  4  inches 
thick  receive  from  0.234  to  0.41  ton-miles  per  sq.  yd.,  or  2.99  to 
3.78  ton-miles  per  cu.  yd.j  The  number  of  passages  of  the  roller 
varies  from  75  to  100.     In  Paris  some  streets  were  "  thrown  open 

*  Trans.  Amer.  Soc.  Civil  Eng'rs,  Vol.  8,  p.  105-6. 

\lbid.,  p.  107. 

%  Ibid.,  Vol.  41,  p.  127. 

%  Ibid.,  p.  138. 

\\Ibid.}  Vol.  8,  p.  104. 


ART.   2.]  CONSTRUCTION.  229 

to  traffic  when  the  rolling  had  reached  about  the  point  when  in  this 
country  the  application  of  screenings  would  commence."  *  It  is 
believed  that  the  American  roads  are  enough  better  to  pay  for 
the  greater  amount  of  rolling  they  receive.  As  a  rule,  American 
crushed-stone  roads  are  better  constructed  than  those  in  Europe, 
notwithstanding  the  fact  that  the  European  roads  are  frequently 
cited  as  models  for  imitation  in  America.  The  superiority  of 
American  roads  is  partly  due  to  the  greater  amount  of  rolling  they 
receive,  and  partly  to  the  greater  quantity  and  better  quality  of 
binding  material  used.  As  a  rule  the  broken-stone  roads  are 
better  maintained  in  Europe  than  in  America — probably  because 
of  the  cheaper  hand  labor. 

345.  BINDING  THE  ROAD.  The  interstices  between  the  frag- 
ments of  stone  should  be  filled  with  a  fine  material  which  will 
act  mechanically  to  keep  out  the  rain  water  and  thereby  keep 
the  subgrade  dry,  and  also  to  support  the  fragments  and  pre- 
vent them  from  being  broken,  and  which  will  act  physically 
and  possibly  also  chemically  to  bind  or  cement  the  fragments 
into  a  single  more  or  less  solid  mass.  The  proper  binding  of  the 
stone  is  the  most  important  part  of  the  construction  of  a  broken- 
stone  road. 

The  material  employed  to  fill  the  interstices  in  a  broken -stone 
road  is  usually  called  the  binder,  and  sometimes  the  filler. 

346.  Nature  of  the  Binder.  The  binding  material  or  the  filler 
should  be  finely  divided  so  as  to  be  easily  worked  into  the  inter- 
stices, should  have  a  considerable  resistance  to  crushing  so  as  to 
properly  support  the  pieces  of  crushed  stone;  and  should  not 
change  its  physical  condition  when  wet.  Various  materials  have 
been  employed — clay.  loam,  shale,  sand,  and  limestone  and  trap- 
rock  screenings. 

Clay  and  loam  are  frequently  used.  Their. merit  is  that  they  are 
cheap,  are  easily  applied,  and  have  a  high  cementing  power  (see 
Table  20.  page  187) ;  but  they  are  easily  affected  by  water  and 
frost,  and  when  wet  act  more  as  a  lubricant  than  as  a  binder. 
Clay  or  loam  binder  will  give  a  smooth  road  without  much  rolling, 
but  such  a  road  is  liable  to  be  very  dusty  in  dry  weather,  and  muddy 

♦Trans.  Amer.  Soc.  Civil  Eng'rs,  Vol.  8,  p.  105. 


230  BROKEN-STONE   ROADS.  [CHAP.  V. 

in  wet  weather.  When  clay  or  loam  is  employed  as  a  binder,  the 
utmost  care  should  be  taken  that  no  more  is  used  than  just  enough 
to  fill  the  voids. 

Shale  and  slate  are  only  hard  and  compact  clay,  and  their  only 
merit  is  that  they  give  a  smooth  surface  with  but  little  rolling.  They 
arc  speedily  reduced  to  dust,  and  then  have  all  the  disadvantages 
of  clay.  They  have  fair  cementing  power — see  Table  20, 
page  187. 

Sand  is  often  used  as  a  filler,  and  if  composed  of  fine,  clean,  hard 
grains,  gives  fair  results;  but  sand  which  is  resistant  enough  for  a 
good  binding  material  usually  consists  of  silica  or  quartz,  neither 
of  which  has  a  high  cementing  power  (Table  19  and  20,  page  186). 
If  the  grains  are  coated  more  or  less  with  iron  oxide,  or  if  accom- 
panied by  bits  of  ironstone  (clay  cemented  with  iron  oxide),  sand 
makes  an  excellent  binding  material,  since  the  iron  possesses  con- 
siderable cementing  power.  This  form  of  binder  is  particularly 
valuable  in  making  repairs  over  an  opening  when  a  roller  is  not 
available,  or  when  water  for  washing  in  the  binder  is  scarce.  Low- 
grade  iron  ore  has  been  used  for  a  binder — either  alone  or  mixed 
with  stone  dust. 

Fine  screenings — the  finest  product  of  the  stone  crusher,  say, 
from  \  or  \  inch  to  dust — from  the  stone  used  in  the  body  of  the 
course  is  the  most  desirable  material  for  a  binder,  partly  because 
it  helps  to  utilize  the  entire  product  of  the  crusher,  partly  be- 
cause of  its  high  crushing  strength,  and  partly  because  the  stone 
is  usually  selected  for  the  high  cementing  power  of  its  dust.  Lime- 
stone has  very  high  cementing  power,  but  is  soft  and  pliable.  Trap 
has  a  fair  cementing  power,  and  is  hard  and  durable.  Limestone 
screenings  require  less  rolling,  but  the  trap  dust  makes  a  more 
durable  road. 

Sometimes  the  detritus  removed  from  the  surface  of  a  stone  road 
during  maintenance  or  preparatory  to  making  repairs,  is  employed 
as  a  binder.  At  best,  such  material  is  very  poor  for  this  purpose. 
It  is  worn  out  and  has  performed  its  duty;  and,  besides,  it  is  com- 
posed largely  of  manure  and  vegetable  and  earthy  matter — all  of 
which  are  very  undesirable  in  a  binder.  Such  detritus  is  more 
valuable  as  a  fertilizer  than  as  a  road  material. 

347.  Applying  the  Binder.     There  is  a  difference  of  opinion 


ART.   2]  CONSTRUCTION.  231 

among  competent  engineers  as  to  the  best  method  of  applying  the 
binding  material.  Some  apply  it  on  the  top  of  each  course,  and 
some  on  top  of  only  the  last  course.  In  the  first  case,  all  the  voids 
from  the  bottom  to  the  top  of  the  road  are  filled  with  fine  material; 
in  the  second  case,  the  binder  usually  fills  the  voids  of  the  top 
course  only.  Those  who  advocate  the  first  method  claim  that  the 
whole  mass  should  be  filled  to  prevent  the  stones  from  moving 
under  the  traffic,  and  also  to  prevent  the  soil  from  working  up 
from  below;  while  the  advocates  of  the  second  method  claim  (1) 
that  filling  the  top  layer  is  sufficient  to  hold  the  stone  in  place  near 
the  surface,  (2)  that  the  stones  of  the  lower  courses  have  no  ten- 
dency to  move,  (3)  that  the  unfilled  voids  of  the  lower  course  pro- 
mote drainage,  and  (4)  that  as  the  upper  layer  wears  away,  the 
dust  will  wash  down  into  the  lower  open  spaces  in  such  a  manner 
as  always  to  keep  the  3  or  4  inches  just  below  the  surface  properly 
bound.  If  the  stone  is  hard,  or  if  the  lower  courses  are  not  thor- 
oughly rolled,  applying  the  binding  material  only  on  the  top  of 
the  last  course  practically  fills  the  voids  to  the  earth  foundation;  but 
of  course  it  is  cheaper  to  apply  the  filler  on  the  top  of  each  course 
than  to  attempt  to  fill  all  of  the  voids  by  applying  it  on  the  top 
course  only.  If  the  stone  in  the  lower  courses  is  soft,  or  if  the  top 
of  the  next  to  the  last  course  is  thoroughly  rolled,  applying  the 
binder  on  the  top  fills  the  voids  in  the  top  course  only.  It  is  suffi- 
cient to  fill  the  voids  of  the  top  course. 

The  binder  is  applied  by  spreading  a  layer  of  "  fines"  about  half 
an  inch  thick  over  the  partially  rolled  surface.  The  filler  should 
be  dumped  upon  a  board  platform,  and  not  directly  upon  the  road 
surface;  and  should  be  distributed  evenly  over  the  stone  with  a 
shovel.  Under  no  consideration  should  loam  or  vegetable  matter 
be  allowed  to  contaminate  the  stone  screenings.  After  the  binding 
material  has  been  evenly  distributed,  the  surface  is  then  sprinkled 
and  rolled.  The  sprinkler  should  have  many  fine  openings,  the 
object  being  to  give  a  gentle  shower  rather  than  a  violent  flooding. 
The  water  washes  the  fine  material  into  the  cavities  belov.-,  and  the 
roller  crushes  the  small  fragments  and  makes  more  dust.  The 
rolling  also  aids  in  working  the  binder  into  the  mass;  in  fact,  the 
binder  can  be  worked  in  to  a  considerable  extent  by  dry  rolling, 
and  consequently  the  quantity  of  water  used  varies  widely  with 


232  BROKEX-STOKE   ROADS.  [CHAP.  V. 

the  method  of  doing  the  work,  but  is  usually  about  4  to  6  cubic 
feet  per  cubic  yard  of  stone.  Sometimes  men  with  heavy  brooms 
are  kept  upon  the  road  sweeping  the  binding  material  about  to  assist 
in  working  it  in,  and  also  to  secure  a  more  uniform  distribution  of  it. 
While  applying  the  screenings  care  should  be  taken  to  pick  off  any 
coarse  stone — particularly  flat  ones, — as  they  do  not  bind  well  and 
their  subsequent  loosening  causes  the  road  to  ravel  (§  377). 

As  the  rolling  and  sprinkling  proceed,  fine  material  should  be 
added  where  needed,  i.  e.,  as  open  spaces  appear.  All  the  filler 
should  not  be  put  on  in  the  beginning,  since  a  thin  layer  can  be 
worked  in  to  better  advantage  than  a  thick  one;  and,  besides,  it 
is  desirable  to  use  only  enough  to  fill  the  voids. 

Occasionally  the  surface  of  the  road  becomes  muddy  and  sticks 
to  the  roller.  This  can  be  remedied  in  either  of  two  ways:  viz., 
by  sprinkling  the  roller  and  keeping  it  constantly  wet,  or  by  keep- 
ing the  sprinkling  wagon  immediately  in  front  of  the  roller  and 
having  the  binder  always  fully  saturated.  The  rolling  is  con- 
tinued until  the  water  is  forced  as  a  wave  in  front  of  the  roller 
and  until  the  surface  behind  the  roller  is  mottled  or  puddled  and 
is  covered  with  a  thin  paste.  The  binding,  or  the  puddling  of 
the  surface,  can  not  be  done  satisfactorily  when  the  surface  freezes 
nightly. 

When  finished,  if  the  road  is  allowed  to  diy  and  is  then  swept 
ciean,  the  surface  will  be  seen  to  have  the  appearance  of  a  rude 
mosaic,  the  flat  faces  of  the  fragments  of  stone  being  crowded 
against  one  another  and  the  interspaces  being  filled  with  the  bind- 
ing material — the  latter  occupying  about  half  of  the  area.  Such  a 
surface  when  dry  will  stand  considerable  sweeping  with  a  steel 
broom  or  brush  without  the  fragments  of  stone  being  loosened. 
The  water  used  in  construction  not  only  aids  in  working  the  binder 
into  the  interstices,  but  also  develops  the  cementing  power  of  the 
rock  dust. 

348.  Usually  after  the  rolling  has  been  completed  a  thin  coat- 
ing of  binding  material  is  sprinkled  over  the  surface.  Authorities 
differ  as  to  the  amount  of  fine  material  to  be  left  on  the  finished 
surface,  some  specifying  as  little  as  £  inch  and  some  as  much  as  1 
inch,  the  usual  quantity  being  f  to  J  inch.  If  only  enough  binding 
material  to  fill  the  interstices  between  the  coarser  fragments  is  left 


ART.   2. j  CONSTRUCTION.  233 

upon  the  road,  the  fine  material  will  be  blown  and  washed  away, 
and  soon  there  will  not  be  enough  to  level  up  between  the  large 
bits  and  to  hold  the  surface  stones  in  place,  when  the  wear  will 
come  directly  upon  the  stones.  On  the  other  hand,  if  any  con- 
siderable quantity  of  fine  material  is  left  upon  the  surface,  it  is 
speedily  ground  up,  and  becomes  offensive  dust  if  it  is  not  sprinkled, 
and  equally  objectionable  mud  if  it  is  sprinkled.  It  is  probably 
best  to  put  on  a  quantity  just  sufficient  to  give  a  thin  layer,  say, 
-J  to  |  inch,  over  the  surface,  and  when  this  amount  is  blown  or 
washed  away  renew  it.  By  this  method,  the  wear  on  the  body  of 
the  road  will  be  prevented,  a  minimum  amount  of  sprinkling  will 
be  required,  and  there  will  be  as  little  dust  as  possible.  The  surface 
coat  is  also  serviceable  in  decreasing  the  tendency  of  the  binding 
material  to  dry  out  and  to  lose  part  at  least  of  its  cementing  power; 
i.  e.,  the  surface  coat  is  serviceable  to  prevent  the  raveling  of  the 
road  (see  §  377).  Fine  material  over  and  above  that  required  to 
fill  the  interstices  is  useful  only  to  prevent  raveling  and  to  keep  the 
wear  from  the  surface  of  the  stone ;  and  therefore  sand  is  as  good 
for  the  top  dressing  as  stone  dust,  and  is  usually  much  cheaper. 
Loam  or  clay  does  fairly  well  for  a  top  dressing,  but  it  readily 
grinds  to  dust  and  blows  away  when  dry,  and  when  wet  makes  mud. 
It  is  desirable  that  this  coat  of  fine  material  shall  be  sprinkled  and 
rolled  before  the  traffic  is  admitted. 

The  road  is  now  finished;  and  after  it  has  dried  out  for  a  day 
or  two,  it  may  be  thrown  open  to  traffic. 

349.  Amount  of  Binder.  The  amount  of  binder  required  de- 
pends upon  the  hardness  of  the  stone  and  the  amount  of  rolling 
preceding  the  application  of  the  binder  (see  §  347).  The  voids  in 
the  broken  stone  can  be  reduced  by  rolling  to  20  or  25  per  cent,  say 
22  per  cent,  of  the  compacted  mass ;  *  and  the  completed  road  will 
contain  4  to  7  per  cent,  say  5  per  cent,  of  voids ;  f  and  therefore 
enough  binder  must  be  added  to  fill  about  17  (  =  22  — 5)  per  cent  of 
voids.  The  binder  itself  usually  contains  40  to  50  per  cent  of  voids, 
and  therefore  the  volume  of  filler  required  is  40  to  50  per  cent  more 


♦Codrington's  Maintenance  of  Macadam  Roads,  p.  25  and  52.    London,  1870. 

fH.  P„  Gillette  in  Economies  of  Road  Construction,  p.  19  and  32,  and  M.  Leon 
Durand-Claye,  Engineer-in-Chief,  Department  of  Roads  and  Bridges,  Erance,  in 
Annates  des  Ponts  et  Chausse'es,  as  quoted  in  Engineering  Record,  Vol.  25,  p.  232. 


234  BROKEN-STONE    ROADS.  |  CHAP.   V. 

than  the  voids  to  be  filled,  i.  e.,  40  to  50  per  cent  more  than  17  per 
cent  of  the  original  volume  of  stone ;  or,  in  other  words,  the  amount 
of  filler  required  is  25  to  35  per  cent  of  the  thickness  filled.  This 
allows  a  little  for  waste  and  for  the  thin  coating  spread  upon  the 
finished  surface.  If  the  binder  is  applied  before  the  rolling  has 
progressed  very  far,  more  fine  material  will  be  required,  since  some 
of  it  will  work  in  between  the  fragments  of  stone  and  prevent  them 
from  coming  into  as  close  contact  as  they  otherwise  would.  In 
this  case,  part  of  the  surplus  binder  will  be  flushed  to  the  surface 
during  the  sprinkling  and  rolling,  as  mortar  flushes  to  the  surface 
in  tamping  concrete;  but  in  no  case  does  all  the  surplus  thus  work 
out,  and  consequently  the  road  is  not  as  durable  as  though  only 
enough  binder  had  been  used  to  fill  the  voids;  and,  farther,  the 
binder  which  flushes  to  the  surface  must  be  removed  as  mud.  An 
excess  of  binder  is  often  used  to  reduce  the  cost  of  construction 
by  decreasing  the  amount  of  sprinkling  and  rolling  required;  but 
such  a  practice  adds  to  the  cost  of  maintenance,  and  the  road  is 
less  durable  and  more  dirty. 

350.  Cost  of  Construction.  The  cost  of  construction  of  a 
crushed-stone  road  varies  greatly  with  the  size  of  the  job,  the  con- 
ditions of  the  material  and  labor  markets,  the  specifications  under 
which  the  work  is  done,  etc. ;  and  any  general  statements  must  be 
considered  only  as  approximate  for  any  particular  case. 

351.  Cost  of  Quarrying.  The  cost  of  quarrying  will  vary  with 
the  amount  of  stripping,  the  hardness  of  the  rock,  the  depth  of  face, 
the  method  of  quarrying  (hand  tools  or  explosives),  the  method 
of  drilling  (hand  or  pov/er),  etc.  For  herd  limestone,  the  cost  of 
quarrying,  exclusive  of  quarry  rent,  pumping,  and  superintendence, 
was  as  in  Table  21,  page  235. 

Table  22,  page  235,  gives  the  detailed  cost  of  quarrying  road 
stone  in  Great  Britain.  Wages  v/ere  probably  less  than  in  Amer- 
ica, and  probably  the  labor  was  correspondingly  less  efficient.  In 
quarry  No.  1,  the  rock  was  "  highly  siliceous  and  very  seamy  in 
parts,  60  per  cent  being  very  hard  and  solid."  In  No.  2,  the  rock 
was  "  hard  and  tough,  and  seamy  in  places."  No.  3  was  a  "  hard 
and  very  tough  basalt." 

For  additional  data  on  the  cost  of  quarrying,  see  the  first  part 
of  Table  23,  page  237. 


ART.   2.] 


CONSTRUCTION. 


235 


TABLE  21. 
Cost  qf  Quarrying  Hard  Limestone  Exclusive  of  Quarry  Rent, 
Pumping,  and  Superintendence.* 
Results  in  Cents  per  Cubic  Yard. 


6 

Items  of  Expense. 

Depth  of  Drill  Holes,  Feet. 

01 

1 

2 

3 

4 

6 

8 

10 

12 

1 

Dynamite 

26 
66 

18 
32 

15 
22 

13 

17 

11 

10 

9 
9 

8 

7 

7 

% 

Drilling 

6 

Cost  of    quarrying,  —  solid 
stone 

3 

92 

92 
15 

50 

45 

15 

37 

30 
15 

30 

23 
15 

21 

15 
15 

18 

13 
15 

15 

9 
15 

13 

4 

Cost  of    quarrying,  —  loose 
stone 

8 

5 

Sledging   and   throwing   back 
from  quarry  face 

15 

Total  cost 

fi 

107 

60 

45 

38 

30 

28 

24 

?3 

♦Gillette's  Economics  of  Road  Construction,  p.  26. 


TABLE  22.. 

Actual  Cost  of  Quarrying  Road  Stone.^ 

Cents  per  Ton  (2,000  pounds). 


c 

Items. 

Quarry. 

t 

No.  1. 

No.  2. 

No.  3. 

i 

Stripping 

4.1 

3.6 

1.9 
5.5 

1.4 

2.7 

2.1 
5.4 

1.0 

2 
3 

Drilling — hire  of  engine,  coal,  water,  dress- 
ing drill-bits,  depreciation  of  drill,  etc 

Blasting — dynamite,  detonators,  wire  and 
wiring,  charging  and  tamping 

3.3 
2.3 

4 

Sledging  to  size  for  9"  X  16"  breaker 

6.5 

Total 

15.1 

4  158 
33 

11.6 

3  475 

22 

13.1 

5 

Number  of  tons  quarried 

2  102 

6 

Height  of  vertical  face,  feet 

18 

f  Road  Making  and  Maintenance,  Thomas  Aitken,  p.  170-72.    London,  1900. 


236  BROKEN-STONE   ROADS.  CHAP.    Y.] 

352.  Cost  of  Setting  Telford.  The  cost  of  setting  a  telford 
foundation  will  vary  greatly  with  the  character  of  the  stone  and 
with  the  amount  of  knapping  and  wedging  done.  If  the  founda- 
tion stones  are  laminated,  they  will  fit  well  one  against  the  other 
and  consequently  require  comparatively  little  wedging,  but  if  the 
stone  is  unstratified  and  breaks  in  irregular  pieces,  more  labor  wilJ 
be  required  to  place  it  and  to  break  off  projecting  points  and  to  wedge 
the  stones.  On  the  Hudson  County  Boulevard  (Jersey  City.  N.  J.) 
three  men  set,  dressed,  and  thoroughly  wedged  about  3  square 
yards  of  trap  telford  foundation  per  hour,  the  stone  being  wheeled 
from  the  side,  at  a  total  cost  for  labor  of  about  15  to  18  cents  per 
square  yard.  With  a  soft,  bedded  stone,  the  cost  is  only  about  5 
to  6  cents  per  square  yard. 

On  the  state-aid  roads  in  Massachusetts,  in  1899  the  average 
contract  price  for  a  6-inch  telford  foundation  in  place  was  34  cents 
per  sq.  yd.,  the  minimum  being  30  cents  and  the  maximum  50.* 

353.  Cost  of  Crushing.  The  cost  of  crushing  varies  with  the 
amount  of  the  output,  the  arrangement  of  the  plant  (§  330),  the 
hardness  of  the  stone,  the  price  of  labcr  and  supplies,  etc.  Table 
23,  page  237,  gives  the  details  for  four  kinds  of  stone.  Notice  that 
for  the  ledge  stone,  the  output  was  80  to  100  cubic  yards  per  day, 
and  the  cost  of  crushing  was  20  and  21  cents  respectively.  If  the 
output  is  decreased,  the  price  will  be  slightly  increased,  and  vice 
versa.  A  study  of  numerous  data  seems  to  show  that  the  above 
is  fairly  representative,  except  that  frequently  the  prices  paid  for 
labor  are  less. 

354.  Price  of  Crushed  Stone.  Crushed  limestone  is  occasion- 
ally sold  f.o.b.  at  the  quarry  as  low  as  35  to  40  cents  per  ton  (about 
47  to  53  cents  per  cu.  yd.),f  and  frequently  as  low  as  45  to  50  cents 
per  ton  (60  to  65  cents  per  cubic  yard).  The  cost  of  crushed  trap 
f.o.b.  at  the  quarries  in  New  Jersey,  for  several  years  previous  to 
1900,  was  40  to  50  cents  per  ton;  but  in  that  year  it  was  increased 
nearly  50  per  cent.|  In  Massachusetts,  the  cost  of  broken  trap 
varies  from  $1.10  to  $1.60 per  ton  (about  $1.47  to  $2.13  per  cu.yd.) 

*  Report  of  Massachusetts  Highway  Commission  for  1903.  p.  106-09. 
f  A  cubic  yard  of  screened  limestone  is  usually  considered  as  weighing  2,600 
or  2,650  pounds. 

%  Report  of  New  Jersey  Commissioner  of  Public  Roads,  1900,  p.  43. 


AET„  2.] 


CONSTRUCTION. 


237 


TABLE  23. 

Detailed  Cost  of  Crushing  Stone.* 

Cents  per  Cubic  Yard. 


d 

Items. 

Greenish 
Trap 
Ledge 
Stone. 

Conglom- 
erate 
Ledge 
Stone. 

Cobble 
Stone 

largely 
Trap. 

Cobble 

Stone 

largely 

Granite. 

1 

Labor  drilling — steam 

9.2 

2 

"            "         hand  .  . 

24.9 
1.8 
2.3 

42.0 

R 

Coal,  oil,  waste,  repairs,  and  powder. 
Sharpening  drills  and  tools 

8.4 

6.9 

27.9 

4 

5 

Breaking  stone  for  crusher 

Cost  of  preparing  for  crusher 

Filling  carts 

6 

52.5 

71.0 

7 

9.8 

7.2 

12.7 
6.2 

14  4 

8 

Hauling  to  crusher 

3i.4         9  8 

Cost  of  delivering  to  crusher 

Feeding  crusher 

9 

17.0 

18.9 

31.4        24.2 

10 

5.3 
3.1 
7.9 
4.1 

5.3 

3.8 
5.0 

3.3 
2.9 
4.5 

6  5 

11 

Engineer  for  crusher   . 

3  6 

12 

Coal,  oil,  waste,  and  repairs 

4  4 

13 

Repairs 

Moving  and  setting  up  crusher 

1  1 

14 

2.3 

4.9 

"2A 

1  9 

15 

Watchman 

2  9 

Cost  of  crushing  .                  

16 

20.4 
52.5 
17.0 

21.3 
71.0 
18.9 

13.1 

20  4 

17 

"     ''   preparing  for  crusher 

"      "  delivering  to  crusher 

"     "  crushed  stone  in  bin 

Cost  of  crushing  stone  per  ton  (2  000 
\b.) 

18 

31.4 

24.2 

19 

89.8 

111.2 

44.5        44.6 

20 

$0.74 

3  805 

9.0 

$3.00 
2.40 
1.25 
2.00 
2.50 

$0.88 
1620 
11.2 

$3.00 
2.50 

"2.2h 
2.25 
1.75 
1.50 
1.00 
5.00 
5.25 
11.34 

$0.33 
1  587 
15.7 

$3.00 

$0.33 

21 

Total  amount  crushed,  tons 

2  399 

22 

Tons  crushed  per  hour 

12.1 

23 
?4 

Prices  paid  above 

Foreman,  per  day  of  9  hours 

Operator  of  steam  drill 

$3.00 

25 

Stoker  for  steam-drill  boiler 

*  2.66" 

26 

Engineer  for  stone  crusher 

3.00 

27 

i  Blacksmith    

28 

Watchman 

1.75 

1.50 
1.25 
5.00 
5.25 

1.75 

29 

Common  labor 

1.75 

1.75 

30 

Water  bov 

31 
32 
33 

1  One  driver  and  two  1-horse  carts. . .  . 
i  Coal— anthracite,  per  2  000  lb 

5.00 

5.25 

11.34 

5.00 
5.25 

*A.  F.  Noyes,  City  Engineer  of  Newton,  Mass.,  in  Keport  of  Massachusetts 
Highway  Commission  for  1893,  p.  93-107. 


238  BR0KE}$r-ST0XE    ROADS.  [CHAK  V. 

on  cars  at  the  end  of  the  railroad  transportation.*  In  Boston, 
the  cost  of  crushed  granite  delivered  on  the  streets  is  $1.65  to  $1.90 
per  ton.  In  Montreal,  syenite  macadam  delivered  on  the  street 
costs  an  average  of  $1.15  to  $1.20  per  ton. 

355.  Cost  of  Hauling.  We  will  assume  that  the  wages  of  driver 
and  team  is  30  cents  per  hour,  although  in  cities  it  will  usually  be 
more  than  this.  'A  load  will  vary  from  1  to  1 J  cubic  yards,  the  for- 
mer on  soft  roads  and  the  latter  with  good  ones ;  and  we  will  assume 
that  1}  yards  is  an  average  load.  When  the  stone  is  stored  in 
bins,  it  will  require  about  5  minutes  to  load;  and  an  equal  time 
will  be  consumed  in  dumping.  The  cost  of  the  time  consumed  in 
loading  and  unloading,  then,  is  one  sixth  of  the  hourly  wages  of 
the  team  and  driver,  or  5  cents  per  load,  which  is  equal  to  four  cents 
per  cubic  yard.  The  team  can  easily  travel  2\  miles  per  hour,  or  220 
feet  per  minute;  but  to  allow  for  little  delays,  we  will  assume  that 
the  team  averages  100  feet  and  return  per  minute,  at  a  cost  of  0.5 
cents  per  load  or  0.4  cents  per  cubic  yard.  The  cost  of  hauling, 
then,  is  4  cents  for  loading  and  dumping  plus  0.4  cent  per  100  feet 
of  distance  hauled.  This  is  equivalent  to  25  cents  for  a  haul  of 
1  mile. 

356.  Cost  of  Spreading.  The  cost  of  spreading  will  depend 
upon  whether  it  is  dumped  upon  a  wood  platform  and  spread  by 
hand,  or  upon  the  road  and  spread  with  a  road  grader  (§  333). 
The  average  cost  of  the  first  process  on  state-aid  roads  in  Massa- 
chusetts is  4  cents  per  ton  or  6  cents  per  cubic  yard ;  f  while  with  a 
road  grader  the  cost  of  spreading  is  about  2  cents  per  cubic  yard, 
including  the  hand  labor  in  completing  the  leveling.  J 

357.  Cost  of  Sprinkling.  The  cost  of  sprinkling  is  an  extremely 
variable  item,  depending  upon  the  source  of  the  water  supply 
and  the  nature  of  the  subgrade.  It  will  require  at  least  4;  and 
possibly  16,  cubic  feet  of  water  per  cubic  yard  of  stone.  "One 
man  with  a  good  hand  pump  will  raise  1,000  cu.  ft.  of  water  16  ft. 
high  in  10  hours  into  a  tank  from  which  it  can  be  drawn  off  into 
the  sprinklers.  If  the  product  of  two  good  portable  crushers  is 
going  into  the  road,  it  will  take  about  300  cu.  ft.  of  water  daily  to 

*  Report  of  Massachusetts  Highway  Commission,  1901,  p.  16. 

f  Ibid.,  1894,  p.  30. 

J  Gillette's  Economics  of  Road  Construction,  p.  29. 


ART.  2.]  CONSTRUCTION.  239 

puddle  the  macadam  and  an  equal  amount  to  keep  the  subgrade 
in  compact  condition,  although  in  very  sandy  soil  twice  as  much 
water  may  be  needed.  One  man  will  therefore  pump  enough  water 
for  80  cu.  yds.  of  crushed  stone  and  for  the  subgrade,  at  a  cost  of 
2  cts.  per  cu.  yd.  of  stone.  A  sprinkler  holding  60  cu.  ft.  of  water 
is  ordinarily  used,  which  at  $4  per  day  for  team,  cart,  and  driver 
will  supply  all  the  water  needed,  up  to  a  haul  of  1J  miles  from  the 
storage  tank.  A  sprinkler  can  be  loaded  in  ten  minutes,  and  with 
the  speed  of  team  at  220  ft.  a  minute,  or  2\  miles  an  hour,  it  is  easy 
to  estimate  the  number  of  trips  a  day  and  the  number  of  sprinklers 
that  will  be  needed  for  different  lengths  of  haul.  Ordinarily  one 
sprinkler  is  required  for  each  roller,  so  that  the  cost  of  sprinkling 
will  be  10  cents  per  cu.  yd.,  which,  added  to  the  cost  of  pumping, 
makes  a  total  of  12  cts.  per  cu.  yd.  of  stone;  but  with  a  long  haul 
in  sandy  soil  the  cost  frequently  runs  as  high  as  20  cts.  per  cu.  yd."  * 

358.  Cost  of  Rolling.  The  amount  of  rolling  varies  greatly 
with  the  amount  and  character  of  the  filler  employed  (§  346-49), 
and  consequently  there  is  a  very  great  difference  in  the  cost  for 
different  cases.  Unfortunately  the  published  reports  upon  the 
cost  of  rolling  are  very  meager,  and  seldom  fully  state  the  items  of 
expense  included;  and  some  are  based  upon  time,  some  upon  area, 
and  others  upon  quantity  with  little  or  no  data  as  to  the  thick- 
ness of  the  course,  the  kind  of  stone,  the  character  of  binder,  etc. 
The  actual  daily  expenditures  for  operating  the  roller  vary  with 
the  cost  of  labor,  coal,  water,  etc. ;  and  the  total  daily  cost  of  opera- 
tion depends  upon  the  amount  of  work  done  per  season,  i.  e.,  upon 
the  number  of  days  over  which  the  cost  of  interest,  storage,  and 
depreciation  is  to  be  distributed. 

On  Massachusetts  state-aid  roads,  in  1894,f  seven  towns  owning 
steam-road  rollers  (mostly  12-ton)  ran  them  at  an  average  daily 
cost  of  $5.42,  the  maximum  being  $6.46  and  the  minimum  $3.72; 
and  ten  towns  using  hired  rollers  (mostly  12-ton)  ran  them  at  an 
average  daily  expense  of  $15.94,  the  maximum  being  $24.46  and 
the  minimum  $6.62.  The  cost  for  the  first-mentioned  towns 
probably   does    not   include   interest,   storage,   and   depreciation; 


♦Gillette's  Economics  of  Road  Construction,  p.  31. 

\  Report  of  Massachusetts  Highway  Commission  for  1895,  p.  40-41. 


240  BROKEN-STO^E   ROADS.  [CHAP.  V. 

while  that  for  the  second,  included  these  items  and  doubtless  also 
transportation  expenses  and  profits.  In  the  towns  owning  their 
rollers,  the  average  cost  of  rolling  was  13.71  cents  per  cubic  yard, 
or  4.05  cents  per  square  yard;  and  the  average  amount  rolled  per 
day  was  59  cubic  yards,  the  maximum  being  102  and  the  minimum 
14.  In  the  towns  hiring  rollers,  the  average  price  was  25.1  cents 
per  cubic  yard,  or  8.8  cents  per  square  yard;  and  the  average 
amount  rolled  per  day  was  71  cubic  yards,  the  maximum  being 
139  and  the  minimum  31. 

359.  Cost  of  Finished  Road.  The  total  cost  of  the  road  varies 
with  the  amount  of  grading  and  drainage  required,  the  length 
improved  in  a  single  season,  the  length  of  railroad  and  wagon  haul, 
the  specifications,  etc. 

360.  New  Jersey.  In  northern  New  Jersey,  the  total  cost  of 
trap  macadam  roads  4  to  6  inches  deep,  where  the  rock  was  obtained 
near  the  road,  ranged  from  20  to  45  cents  per  square  yard;  and 
telford  roads  consisting  of  8  inches  of  telford  and  two  courses  of 
broken  stone  2\  and  1^  inches  thick  respectively,  cost  from  $1.02 
to  $1.29  per  square  yard.  In  the  southern  part  of  that  state, 
where  the  stone  is  transported  20  to  70  miles,  8-inch  trap  macadam 
roads  cost  from  23  to  70  cents  per  square  yard,  the  average  being 
from  50  to  60  cents  per  square  yard.* 

361.  Massachusetts.  The  average  cost  of  220  miles  of  state- 
aid  roads  in  Massachusetts  built  from  1894  to  1899,f  reduced  to 
the  equivalent  cost  of  a  "standard  mile"  (15  feet  wide),  was 
$9,931.23  per  mile  for  construction  and  engineering  expenses, 
exclusive  of  cost  of  administration  and  the  salaries  of  the  chief 
engineer  and  two  assistants.  The  maximum  average  for  the  roads 
in  any  township  was  $20,257.48  and  the  minimum  $4,871.30 
per  "standard  mile."  The  above  gives  an  average  cost  of  $1,126 
per  square  yard,  a  maximum  of  $2,302,  and  a  minimum  of  $0,564. 

In  Massachusetts  in  1897,  52  miles  were  built  in  187  towns 
(townships),  the  average  cost  of  the  several  items  being  as  shown 
in  Table  24,  page  241 4    An  examination  of  the  reports  for  other 


*  Compiled  from  the  Reports  of  the  State  Commissioner  of  Highways  of  New 
Jersey,  1895-1900.  ' 

f  Report  of  Massachusetts  Highway  Commission,  1900,  p.  150-57. 
%Ibid.,  1898,  Appendix  C,  p.  74-75. 


ART.   3.]  MAINTENANCE.  241 

years  indicates  that  the  above  exhibit  is  fairly  representative, 
except  that  the  expenditure  for  stone  is  smaller  than  the  average. 
In  the  state-aid  roads  built  from  1894  to  1899,  the  cost  of  the 
broken  stone  was  equal  to  55  per  cent  of  the  total  cost  of  the  road, 
but  in  later  years  the  amount  of  stone  used  was  decreased. 

TABLE  24. 

Cost  of  Massachusetts  State-aid  Stone  Roads. 

Per  Cent 
Items  of  Expense.  of  Total 

Cost. 

Earthwork  at  32.1  cents  per  cubic  yard 16.4 

Rock  excavation  at  $1.80  per  cubic  yard 2.0 

Shaping  earth  subgrade  at  2.0  cents  per  cubic  yard 2.4 

Gravel  for  foundation  and  wings  at  55.8  cents  per  cubic  yard 3.5 

Telford  foundation  at  33.9  cents  per  square  yard 0.2 

Broken  stone  at   \  $L503  Per  ton  *or  local  stone  I     45.3 

/  $1,920  per  ton  for  trap  ( 

Side  drains  at  34.5  cents  per  lineal  foot 2.7 

Rubble  masonry — dry,  at  $3,133  per  cubic  yard : 2.6 

"             "           in  cement,  at  $5,770  per  cubic  yard 3.3 

Guard  rails  at  16  cents  per  lineal  foot 1.7 

Stone  boundary-posts  at  $1,417  each 0.6 

Paved  cobble  gutters  at  66.0  cents  per  square  yard 1.1 

Vitrified-clay  pipe-culverts — 12-inch,  at  65  cents  per  lineal  foot 1.2 

Land  damages,  catch  basins,  and  minor  items  of  construction 3.0 

Engineering  and  inspection 14 . 0 

Total . 100.0 

362.  New  York.  In  the  State  of  New  York  in  1898,  22  miles 
of  state-aid  macadam  roads  were  built  in  six  sections,  with  an 
average  cost  of  84.0  cents  per  square  yard,  the  maximum  being 
SI. 085  and  the  minimum  64.8  cents.  The  roads  consisted  of  4 
inches  of  native  stone,  and  2  inches  of  trap  rock  bound  with  lime- 
stone screenings.* 

Art.  3.    Maintenance. 

363.  After  the  road  has  been  properly  rolled  and  the  surface 
has  been  made  compact  and  smooth,  it  is  very  desirable  that  it 
should  always  be  maintained  in  that  condition.  Many  seem  to 
believe  that  a  stone  road  is  a  permanent  construction  which  needs 

•'•:  Report  of  New  York  State  Engineer  and  Surveyor,  1899,  p.  37. 


242  BROKEN-STONE    ROADS.  [CHAP.   V. 


no  attention  after  completion;  but  proper  maintenance  is  as  im- 
portant as  good  construction.  The  finest  roads  are  the  result  of 
good  construction  and  a  system  of  maintenance  whereby  every 
defect  is  corrected  before  it  has  time  to  cause  serious  damage. 

364.  AGENTS  OF  DESTRUCTION.  A  broken-stone  road  is  a 
delicately  balanced  construction,  and  is  peculiarly  open  to  the 
destructive  action  of  the  traffic  and  the  weather.  A  careful  study 
of  the  various  agents  of  destruction  is  necessary  to  a  thorough 
understanding  of  the  best  methods  of  construction  and  maintenance. 

The  effect  of  narrow  tires,  equal-length  axles,  small  wheels,  and 
hitching  the  horses  between  the  wheels,  was  considered  in  the 
chapter  on  Earth  Roads — see  §  187-93. 

365.  Effect  of  Wheels.  There  are  three  effects  of  the  passage 
of  a  wheel  over  a  broken-stone  road:  (1)  the  grinding  and  crushing 
action;  (2)  the  effect  of  the  load  in  giving  rise  to  bending  and 
cross-breaking  stresses  throughout  the  whole  thickness  of  the  road 
covering;  and  (3),  when  the  road  metal  is  loose  and  not  bound 
together,  a  displacement  of  the  stones  among  themselves.  If  the 
road  is  properly  rolled  and  a  good  binding  material  is  used,  there 
will  be  no  movement  of  the  stones  among  themselves,  with  a  con- 
sequent wear  and  waste  of  materials;  and  if  the  road  has  a  thick- 
ness proportionate  to  the  load  and  to  the  supporting  power  of  the 
foundation,  there  will  be  no  cross  bending.  Consequently  with  a 
reasonably  well  constructed  road,  the  only  effect  of  the  wheel  is 
its  grinding  and  crushing  action. 

This  effect  of  the  wheel  varies  great \y  with  the  condition  and 
material  of  the  roadway.  If  the  surface  is  perfectly  smooth  and 
the  load  per  unit  of  area  is  not  beyond  the  crushing  resistance  of 
the  stone,  the  amount  of  wear  is  probably  insignificant,  and  possibly 
is  beneficial  to  a  certain  extent,  since  a  certain  amount  of  dust  is 
necessary  to  replace  that  inevitably  swept  away  by  wind  and  water; 
but  the  moment  irregularities  of  any  kind  occur  on  the  surface, 
deterioration  begins,  since  the  wheels  then  immediately  begin  to 
pound.  When  the  pressure  of  the  tire  is  greater  than  either  the 
crushing  strength  of  the  stone  or  the  cohesive  strength  of  the  binder, 
the  damage  is  very  great. 

366.  Horses'  Feet.  It  is  conceded  that  the  picking  of  the 
horses'  feet  is  one  of  the  most  serious  causes  of  damage  to  a  broken- 


ART.   3.]  MAINTENANCE.  243 

stone  road.  The  impact  of  the  shoes  tends  to  displace  the  exposed 
stones  and  to  loosen  the  binding  material;  and  the  dislodgement 
of  one  fragment  makes  it  easier  to  displace  others.  The  surface 
irregularities  produced  in  this  way  are  continually  increased  by 
the  impact  of  the  wheels,  and  the  binding  material  thus  loosened 
is  more  readily  carried  away  by  wind  and  water.  The  breaking 
of  the  binding  material  also  permits  water  to  penetrate  more  easily 
into  the  road-bed.  The  effect  of  the  horses'  feet  is  particularly  de- 
structive on  a  steep  grade — both  in  ascending  and  in  descending. 

367.  Tracking.  The  tendency  of  a  team  to  follow  the  track  of 
the  preceding  vehicle  leads  to  the  formation  of  ruts.  If  drivers 
would  vary  their  track  only  a  few  inches,  one  set  of  wheels  would 
counteract  the  effect  of  the  others,  and  the  road  would  remain 
comparatively  uninjured.  The  advantage  of  this  is  proved  by 
the  fact  that  wherever  there  is  a  turn  in  the  road  the  ruts  disap- 
pear, however  deep  they  may  be  on  the  straight  part,  because  the 
horses  naturally  vary  their  course  round  the  corner,  and  one 
wheel  obliterates  the  track  of  the  preceding  one.  Tracking  is 
easily  remedied  by  a  little  attention  on  the  part  of  the  driver;  and 
to  secure  this,  sign-boards  calling  the  driver's  attention  to  the 
disadvantage  of  tracking,  are  sometimes  set  up.  Legible  signs  at 
each  half  mile  and  at  prominent  points  have  proven  very  effective 
in  preventing  tracking  and  the  consequent  ruts.  Sometimes  piles 
of  stone  or  barricades  are  placed  upon  the  road  to  direct  travel 
temporarily.  The  barriers  are  sometimes  so  arranged  as  to  keep 
the  travel  in  parallel  straight  lines,  and  sometimes  so  as  to  force 
the  traffic  to  move  in  gentle  serpentines.  The  barriers  are  changed 
from  time  to  time  so  as  to  distribute  the  travel  over  every  part  of 
the  road.  This  method  of  limiting  the  travel  is  applicable  only  on 
comparatively  wide  roads ;  and  even  then  it  is  not  defensible,  owing 
to  the  obstruction  of  traffic. 

368.  Wind.  The  strong  winds  which  prevail  over  a  large  part 
of  this  continent,  in  connection  with  long  droughts,  remove  the  dust 
from  between  the  fragments  of  the  stone.  This  effect  is  more  serious 
on  the  less  frequented  highways,  since  the  sparse  traffic  does  not 
make  enough  dust  to  renew  the  cement  in  the  crevices  between 
the  stones,  particularly  as  some  of  it  is  also  liable  to  be  washed 
away  by  rains. 


244  BROKEX-STONE   ROADS.  [CHAP.   Y. 

369.  Rain.  The  action  of  violent  rains  in  destroying  broken- 
stone  roads  is  an  important  factor,  and  somewhat  peculiar  to  this 
country.  The  rain  often  removes  the  binding  dust  between  the 
top  stones  to  such  a  degree  that  they  become  loosened.  This 
effect  is  specially  important  on  slopes  of  considerable  declivity,  as 
is  shown  by  the  "raveling  out"  which  often  occurs  on  steep  grades 
or  on  roads  which  have  an  excessive  crown.  This  indicates  that 
en  grades  the  crown  should  be  only  sufficient  to  turn  the  rain 
water  speedily  into  the  side  ditches. 

A  moderate  amount  of  water,  if  gently  applied,  is  an  advantage 
to  a  broken-stone  road,  since  the  cementing  action  of  the  binding 
material  is  greater  when  wet,  and  for  this  reason  sprinkling  is  an 
important  factor  in  maintenance  (§  380). 

370.  Frost.  Although  freezing  and  thawing  has  little  or  no 
effect  upon  the  individual  pieces  of  stone  (§  737),  frost  has  a  very 
injurious  effect  upon  the  road  as  a  whole.  It  is  desirable  that  the 
binding  material  shall  at  all  times  be  wet,  and  if  the  construction 
is  defective  or  the  maintenance  poor,  there  is  a  liability  of  con- 
siderable water  being  present  in  the  road-bed;  and  this  water  in 
freezing  expands,  breaks  the  bonds,  and  makes  the  road  open  and 
porous.  A  road  that  has  been  well  filled  and  thoroughly  rolled 
will  have  only  a  small  per  cent  of  voids,  and  therefore  there  will  be 
but  little  water  retained  in  the  body  of  the  road  and  consequently 
be  but  little  damage  from  frost. 

371.  Decomposition  of  Stone.  It  is  sometimes  claimed  that 
chemical  decomposition  of  the  stone  is  a  cause  of  deterioration  of 
a  broken-stone  road;  but  this  effect  is  so  small  as  to  be  entirely 
inappreciable.  On  the  contrary,  the  decomposition  of  the  stone 
may  be  an  advantage  to  such  a  road.  Many  of  the  rocks  employed 
in  road  building  are  slightly  soluble  in  water  containing  carbonic, 
nitric,  or  sulphuric  acid  gathered  from  the  atmosphere,  or  in  water 
containing  humic  acid  derived  from  the  decomposition  of  vegetable 
and  animal  matter;  and  consequently  any  rain  or  surface  water 
which  penetrates  a  broken-stone  road  may  dissolve  the  fine  stone 
dust  and  afterwards  deposit  it  in  the  interstices  lower  down, 
where  it  will  act  as  a  cementing  material.  This  may  be,  at  least  in 
part,  the  explanation  of  the  well  known  fact  that  a  crushed-stone 
road,  for  a  time  at  least,  improves  with  age.     The  improvement 


ART.  3.]  MAINTENANCE.  245 

is  doubtless  also  in  part  due  to  the  gradual  infiltration  into  the 
smaller  interstices  of  the  binding  material  of  very  fine  particles 
of  dirt  from  the  surface. 

372.  AMOUNT  OF  WEAR.  The  amount  of  wear  will  vary 
greatly  with  the  climate,  the  amount  and  character  of  the  traffic, 
the  nature  of  the  stone,  and  the  method  of  construction. 

It  has  been  estimated  *  that  in  Great  Britain  20  per  cent  of  the 
wear  was  due  to  atmospheric  causes  and  80  per  cent  to  the  traffic 
and  that  with  fast  stage  coaches  three  fourths  of  the  wear  by  traffic 
was  due  to  horses'  feet  and  one  fourth  to  the  wheels,  while  with  or- 
dinary vehicular  traffic  about  six  tenths  was  due  to  the  horses'  feet 
and  four  tenths  to  the  wheels.  The  relative  wear  from  horses' 
feet  and  wagon  wheels  was  deduced  from  a  comparison  of  the  wear 
of  iron  in  the  horses'  shoes  and  in  the  tires  of  the  wheels;  but  it 
is  not  stated  upon  what  the  estimates  of  the  wear  from  atmos- 
pheric causes  were  based.  Any  such  general  estimate  must  not 
be  considered  as  even  approximately  true  for  any  particular  case, 
since  the  relative  wear  varies  greatly  with  the  exposure  to  sun 
and  wind,  the  drainage,  the  strength  of  the  road,  the  character  of 
the  maintenance,  etc. 

In  France,  where  the  relation  between  the  wear  and  the  traffic 
has  been  carefully  studied,  some  engineers  maintain  that  the  wear 
increases  in  the  same  proportion  as  the  traffic,  while  others  contend 
that  the  wear  increases  in  a  greater  ratio  than  the  traffic.  Table 
25,  page  246,  is  frequently  cited  to  establish  the  latter  view.  These 
data  were  obtained  in  the  following  manner :  Owing  to  the  falling 
in  of  a  tunnel,  the  traffic  on  a  particular  road  was  suddenly  in- 
creased from  its  usual  amount  of  1,378  tons  per  day  to  2,264  tons, 
3,150  tons,  and  5,315  tons  on  different  sections,  at  which  rates 
it  continued  for  74  days,  after  which  it  fell  on  all  portions  of  the 
road  to  1,772  tons  per  day.  The  consumption  of  material  was 
determined  by  measuring  the  amount  of  detritus  removed  from 
the  road  and  also  by  comparing  the  amount  of  material  less  than 
2  centimeters  in  diameter  in  the  body  of  the  road  at  the  beginning 
and  the  end  of  the  period.     According  to  Table  25,  increasing  the 


*  By  Sir  J.  Macneill  before  a  Parliamentary  Committee  in  1831,— see  Codring- 
ton's  Maintenance  of  Macadamized  Roads,  p.  69. 


246 


BROKEX-STOXE    ROADS. 


[CHAP.  T. 


TABLE  25. 

Relation  of  Traffic  and  Wear.* 


Daily  Traffic. 

Annual  Consumption  of 
Materials  per  Mile. 

Annual  Consumption  per 

Mile  per  100  Tons  of 

Daily  Traffic. 

1  378  tons. 

1  772     " 

2  264     " 

3  150     w 
5  315     " 

724  cu.  yd. 
1857   "     " 
2  780  "     u 
4  615   "     " 
9  886   "     " 

52  cu.  yd. 
104   "     " 
122   "     " 
146   "     M 

186   "     " 

traffic  four-fold  increased  the  wear  thirteen-fold;  but  the  case  was 
an  extreme  one,  since  the  increased  traffic  was  unusually  heavy, 
and  since  the  road  material,  schist,  is  unusually  friable  and  defi- 
cient in  cementing  power.  Under  the  1,378  tons  per  day,  the 
wear  was  at  the  rate  of  If  inches  per  annum;  and  under  the  5,315 
tons  per  day,  it  was  at  the  rate  of  more  than  2  feet  a  year.  Appar- 
ently a  majority  of  road  engineers  hold  that  an  increase  of  traffic 
increases  the  wear  per  ton,  but  in  a  much  less  ratio  than  in  Table 
25.  It  is  certainly  true  that  heavy  loads  cause  more  wear  than 
light  ones,  even  when  the  total  weight  transported  is  the  same. 

373.  In  France  careful  observations  are  made  by  the  govern- 
ment engineers  to  determine  the  amount  of  wear  in  terms  of  the 
traffic.  The  traffic  is  expressed  in  "units"  representing  a  horse 
harnessed  to  a  loaded  wagon;  and  to  reduce  the  other  traffic  to 
this  unit,  the  following  values  are  used: 

1.  Each  horse  hauling  a  public  vehicle  or  a  cart  loaded  with  produce  or 

merchandise 1 

2.  Each  horse  hauling  an  empty  cart  or  a  private  carriage \ 

3.  Each  horse,  cow,  or  ox  unharnessed,  and  each  saddle-horse \ 

4.  Each  small  animal  (sheep  or  goat) ..  ^ 

In  1876  the  average  amount  of  material  required  for  the  Routes 
Nationales  was  53  cubic  yards  per  mile  per  100  "units"  of  daily 
traffic,  the  range  for  the  different  departments  being  15  to  265, 
but  usually  from  27  to  102.f  In  1893  the  average  was  49  cubic 
yards  per  mile  per  100  "units"  of  travel,  the  stone  having  an 
average  co-efficient  of  wear  (§  282)  of  10.85. J 

*M.  Graeff   in    Annuales  des  Ponts  et   Chaussdefi,  Vol.  9,  1865 — as   quoted  by 
Codrington  in  Maintenance  of  Macadamized  Roads,  p.  89. 
t  Codrington's  Maintenance  of  Macadamized  Roads,  p.  91. 
X  Rockwell's  Roads  and  Pavements  of  France,  p.  67. 


ART.   3.]  MAINTENANCE.  24? 

374.  In  Austria  the  traffic  has  not  decreased,  but  the  material 
employed  in  repairs  has  continually  decreased  since  1856.  From 
1865  to  1872  the  average  consumption  of  material  was  84.9  cubic 
yards  per  mile  per  annum  per  100  vehicles. 

No  observations  seem  to  have  been  made  to  determine  the 
relation  between  wear  and  traffic  for  English  or  American  roads. 

Professor  Shaler  says:  "If  the  wear  on  macadam  is  more  than 
}  inch  per  year  the  presumption  is  that  true  economy  demands  a 
more  enduring  form  of  pavement."  *  --  ••-  ** — - 

375.  METHODS  OF  MAINTENANCE.  There  are  two  general 
methods  of  maintenance,  which  may  be  called  (1)  continuous 
maintenance  and  (2)  periodic  repairs.  By  the  first  system  the 
waste  on  account  of  traffic  is  supplied  gradually  as  it  is  worn  off 
by  adding  a  patch  here  and  there,  and  so  the  full  thickness  of  the 
road  is  constantly  maintained;  while  by  the  second  system  the 
road  is  permitted  to  wear  thin,  and  then  an  entirely  new  surface 
is  added,  although  this  system  does  not  exclude  small  repairs,  but 
limits  them  to  the  timely  filling  of  holes  and  ruts  to  check  more 
extensive  damage  to  the  road.  The  system  of  constant  mainte- 
nance is  the  one  generally  employed  in  Europe;  while  in  America 
periodic  repairs  seems  to  be  the  more  common,  although  both 
systems  have  their  ardent  advocates. 

Those  favoring  continuous  maintenance  claim  (1)  that  it  is 
the  only  system  that  gives  a  constantly  good  road,  since  with 
periodic  repairs  the  road  is  seldom  good,  being  bad  just  after  repairs, 
becoming  passable  after  a  time,  and  then  deteriorating  until  re- 
paired again;  and  (2)  that  continuous  maintenance  is  the  cheapest 
in  the  long  run.  Those  favoring  the  periodic  system  of  repairs 
claim  (1)  that  a  well  built  road  will  wear  uniformly  until  so  thin 
as  to  need  re-surfacing;  (2)  that  the  system  of  continuous  mainte- 
nance does  not  give  as  good  a  surface  as  the  other  method,  since 
the  new  material  is  constantly  being  added  at  every  point  to  supply 
the  loss  of  wear,  and  this  material  must  be  consolidated  by  the  traf- 
fic; and  (3)  that  the  system  of  maintenance  by  patching  is  exces- 
sively expensive,  requiring  a  needless  amount  of  material  and 
labor. 

*  American  Highways,  p.  224. 


248  BROKEN-STONE    ROADS.  [CHAP.   V. 

There  seems  to  be  an  irreconcilable  conflict  between  the  theories 
of  the  two  sides;  but  in  practice,  under  similar  conditions,  there  is 
not  as  great  a  difference  as  a  statement  of  the  theories  seems  to 
indicate,  the  difference  in  opinion  being  largely  due  to  a  difference 
in  the  conditions  assumed.  In  France,  where  the  maintenance 
of  broken-stone  roads  has  been  the  subject  of  prolonged  and  careful 
observation  by  the  officers  of  the  Corps  of  Roads  and  Bridges,  the 
system  of  continuous  maintenance  is  employed  on  roads  of  mod- 
erate traffic,  i.  e.,  roads  18  to  20  feet  wide  having  a  traffic  not  ex- 
ceeding about  600  tons  per  day;  and  the  system  of  periodic  repairs 
is  employed  upon  roads  of  great  traffic,  i.  e.,  roads  18  to  20  feet 
wide  having  more  than  600  tons  per  day.  These  limits  would 
doubtless  vary  with  the  nature  of  the  road  material,  the  method 
of  construction,  the  climatic  conditions,  the  character  of  the  traffic, 
etc.  It  is  claimed  that  the  system  of  periodic  repairs  "is  growing 
in  favor  in  France,  and  in  1893  more  than  half  the  stone  employed 
in  making  repairs  was  applied  under  this  system.  The  method  is 
used  exclusively  in  general  repairs  of  the  macadamized  streets 
of  Paris."  * 

376.  WORK  OF  MAINTENANCE.  Under  this  head  will  be' dis- 
cussed the  several  kinds  of  work  involved  in  taking  care  of  a  crushed- 
stone  road  and  in  making  repairs. 

377.  Raveling.  One  of  the  chief  evils  to  be  contended  with 
in  the  maintenance  of  a  crushed-stone  road  is  the  tendency  to 
ravel,  i.  e.,  for  one  stone  after  another  to  work  loose  on  the  surface. 
This  occurs  only  after  a  long  dry  spell  or  in  a  road  originally  defi- 
cient in  binding  power,  and  is  more  likely  to  occur  on  lightly 
traveled  roads  than  on  those  having  heavy  traffic.  Raveling  may 
take  place  where  the  wind  sweeps  away  the  binding  material  from 
the  surface,  or  on  a  steep  grade  where  the  water  has  washed  the 
fine  material  away  from  between  the  fragments;  and  is  chiefly 
due  to  the  picking  of  the  horses'  shoes,  and  is  in  a  measure  coun- 
teracted by  the  rolling  action  of  the  wheels. 

At  least  three  expedients  are  employed  to  prevent  raveling. 
1.  Sprinkling  the  road  with  water  effectually  stops  raveling,  and 
causes  the  surface  to  solidify  again.     This  is  the  most  common 


*  Rockwell's  Roads  and  Pavements  of  France,  p.  43.    Wiley,  New  York,  1896, 


ART.  3.]  MAINTENANCE.  249 

- / _ 

remedy  on  city  streets  and  suburban  roads — where  water  is  usu- 
ally convenient  and  plentiful.  For  a  further  discussion  of  Sprink- 
ling, see  §  380.  2.  A  thin  coating  of  coarse  sand  is  very  effective 
in  preventing  raveling.  Ordinarily  on  country  roads  a  layer  half 
an  inch  thick  over  the  middle  8  feet  of  the  trackway  is  sufficient. 
Unless  the  season  is  very  dry  or  the  road  is  unusually  exposed 
to  the  wind,  a  single  application  will  be  enough  for  one  season ;  but 
in  extreme  cases  two  or  even  three  applications  may  be  necessary. 
It  is  important  that  the  sand  be  reasonably  clean  and  coarse,  as 
otherwise  it  will  be  blown  off  by  the  wind  or  be  washed  away  by 
occasional  showers.  If  the  sand  is  accompanied  by  iron  oxide, 
all  the  better,  as  it  adds  to  the  cementing  power  and  aids  in  pre- 
serving an  impervious  covering,  which  tends  to  prevent  evapora- 
tion of  the  moisture  below  the  surface.  The  coating  should  not 
be  very  thick,  or  it  will  yield  under  the  wheel  and  interfere  with 
travel,  besides  being  unsightly.  The  usual  tendency  is  to  add  too 
much  sand,  or  to  substitute  loam  or  clay  for  part  or  all  of  the  sand. 
Clean  coarse  sand  gives  the  best  results.  3.  The  third  method  of 
preventing  raveling  consists  in  incorporating  blue  gravel  or  a  small 
amount  of  hard  pan  or  clay  with  the  stone  screenings  used  for 
surfacing  the  road  during  construction.  The  blue  gravel  and  clay 
are  high  in  cementing  power,  and  when  mixed  with  screenings  make 
a  hard  and  elastic  surface  which  stands  both  wet  and  dry  weather 
reasonably  well,  and  does  not  allow  the  surface  to  ravel. 

378.  Ruts.  Next  after  raveling,  the  tendency  to  form  ruts 
is  the  most  serious  evil  to  be  contended  against  in  the  maintenance 
of  crushed-stone  roads.  Ruts  are  due  either  (1)  to  a  greater  wheel 
load  than  the  road  is  capable  of  standing,  or  (2)  to  the  use  of  an 
inferior  binding  material,  as  loam,  or  (3)  to  tracking  (§  367).  Ruts 
are  most  likely  to  occur  in  the  spring  or  during  a  wet  time,  when 
the  road-bed  is  soft,  and  are  more  common  on  country  roads  than 
on  city  streets,  since  in  the  latter  the  frequent  changes  in  direction 
to  avoid  other  vehicles  produce  a  more  uniform  wTear  over  the 
whole  surface  of  the  road.  A  street-car  track  in  a  broken-stone 
road  prevents  the  distribution  of  traffic  uniformly  over  the  entire 
surface,  and  greatly  increases  the  tendency  to  form  ruts. 

After  ruts  appear  the  onty  remedy  is  to  fill  them  either  with 
new  material  or  by  picking  down  the  sides  of  the  ruts  and  raking 


250  BKOKEK-STO^E    ROADS.  [CHAP.   Y. 

the  loosened  material  into  the  depression.  Usually  the  latter 
course  is  the  wiser,  particularly  on  a  new  road.  Frequently  the 
tendency  to  form  a  rut  may  be  effectually  arrested  by  sweeping 
into  it  the  loose  detritus  from  the  adjacent  parts  of  the  road.  If 
the  road  surface  is  compact  and  hard,  it  may  be  necessary  to 
loosen  the  bottom  and  sides  of  the  rut  before  adding  new  material, 
so  that  the  new  will  thoroughly  unite  with  the  old.  The  new 
material  should  be  of  the  same  character  as  the  old,  as  otherwise 
the  surface  will  wear  unequally  and  become  rough.  For  additional 
suggestions  applying  to  this  subject,  see  §  385. 

379.  Rolling.  In  the  spring  after  the  frost  goes  out,  the  road- 
bed is  soft  and  porous;  and  a  thorough  rolling  with  a  steam  roller 
at  this  time,  before  the  subgrade  is  dry,  is  one  of  the  best  and 
cheapest  methods  of  keeping  a  stone  road  in  good  condition.  Just 
before  this  rolling  is  the  time  to  add  a  little  fresh  surface  material, 
here  and  there,  as  may  be  needed  to  fill  up  slight  depressions.  For 
precautions  to  be  taken  in  filling  these  depressions,  see  §  385. 

380.  Sprinkling.  While  water  in  excess  is  an  enemy  of  crushed- 
stone  roads,  moisture  in  a  moderate  quantity  is  a  great  benefit. 
Moisture  is  necessary  to  preserve  the  cementing  power  of  the  binding 
material,  and  also  to  prevent  an  excessive  removal  of  dust  by  the 
wind ;  and  therefore  sprinkling  to  the  measure  required  to  prevent 
these  injuries  is  an  advantage.  The  water  should  be  applied  in  a 
fine  spray,  and  not  be  allowed  to  run  in  streams  on  the  road;  that 
is,  several  light  sprinklings  are  better  than  a  single  flooding.  If 
sprinkled  too  heavily  or  too  often,  the  road  is  softened  and  breaks 
up  easily. 

Sprinkling  is  usually  employed  on  park  drives  and  city  streets, 
where  it  is  generally  conceded  to  be  true  economy,  without  taking 
into  consideration  the  prevention  of  dust;  but  on  account  of  the 
expense,  it  is  likely  to  be  many  years  before  this  refinement  is 
adopted  for  rural  roads.  The  cost  of  sprinkling  will  vary  greatly 
with  the  cost  of  water  and  the  length  of  haul.  It  has  been  esti- 
mated that  the  annual  expense  of  sprinkling  country  roads  would 
be  $75.00  per  mile  * 

381.  In  some  localities,  particularly  in  California  and  at  the 


Shaler's  American  Highways,  p.  162. 


ART.   3.]  MAINTENANCE.  251 

seaside  summer  resorts  in  New  Jersey,  broken-stone  roads  have 
been  sprinkled  with  crude  petroleum  to  prevent  dust.  The  oil  is 
applied  hot,  with  a  sprinkler,  when  the  road  is  dry,  and  only  in 
such  quantities  as  will  be  readily  absorbed.  An  elastic  cushion 
is  thus  produced,  which  is  practically  impervious  to  water,  and 
which  holds  the  dust  and  screenings  from  blowing  and  washing 
from  the  surface  and  reduces  the  wear  due  to  travel.  From  50 
to  60  barrels  per  mile  are  required  for  the  first  treatment,  and  about 
20  for  each  subsequent  application.  Two  or  three  applications  are 
made  per  year. 

382.  Removal  of  Mud.  Considerable  material  must  be  re- 
moved from  the  road  surface.  Traffic  grinds  the  road  metal  into 
dust,  mud  is  brought  in  from  the  unpaved  side-roads,  and  the 
horses  drop  a  large  amount  of  dung.  All  superfluous  dust  should 
be  removed  for  the  comfort  of  both  travelers  and  adjacent  prop- 
erty owners.  However,  to  prevent  the  surface  stones  from  work- 
ing loose,  it  is  customary  to  keep  the  surface  of  the  road  damp  by 
sprinkling,  and  therefore  the  detritus  to  be  removed  is  chiefly  in 
the  form  of  mud.  The  removal  of  the  mud  prevents  the  formation 
of  tracks,  and  therefore  greatly  decreases  the  tendency  to  produce 
ruts.  An  accumulation  of  mud  retains  water,  which  softens  the 
road  and  increases  the  wear. 

The  more  sticky  mud  is  removed  with  a  shovel  or  a  special 
mud  scraper;  and  the  more  fluid  mass  is  removed  with  brooms. 
A  laborer  by  hand  can  ordinarily  clean  700  to  1,000  square  yards 
per  day.  The  sweeping  should  not  be  so  thorough  as  to  remove 
the  binding  material  from  between  the  surface  stones. 

Mud-scraping  machines  are  upon  the  market  which  consist  of 
a  series  of  narrow  spring  scrapers,  and  which  will  clean  5,000  to 
6,000  square  yards  per  hour  at  a  less  cost  than  can  be  done  by 
very  cheap  hand  labor.  It  is  necessary  to  use  them  with  great 
care,  to  avoid  loosening  the  surface  stones.  Machine  brooms 
are  usually  employed  for  this  work  where  the  road  is  cleaned  at 
frequent  intervals.  The  ordinary  form  consists  of  a  cylindrical 
brush  or  broom  about  16  inches  in  diameter  and  7  feet  long,  attached 
beneath  the  axle  and  connected  by  suitable  gearing  with  the  wheels 
of  a  vehicle  drawn  by  one  or  two  horses.  The  axis  of  the  broom  is 
set  horizontally  at  an  angle  of  about  40  degrees  with  the  axle  of  the 


252  BROKEN-STONE    ROADS.  [CHAP.   V. 

vehicle.  When  working,  the  broom  rests  firmly  on  the  surface 
of  the  pavement  or  road-covering  and  revolves  in  a  direction  oppo- 
site to  that  of  the  wheels,  sweeping  the  dust  sidewise  from  a  strip 
about  5^  feet  wide  and  leaving  it  in  a  ridge  behind  the  rear  end 
of  the  broom.  In  using  this  machine  upon  a  broken-stone  road, 
the  precaution  should  be  taken  to  see  that  the  brush  is  not  too 
stiff.  What  would  be  entirely  suitable  and  in  all  respects  well 
adapted  for  sweeping  pavements  of  stone  blocks,  wood,  or  asphalt, 
might  injure  the  surface  of  a  broken-stone  road  by  penetrating  too 
deeply,  thereby  loosening  the  stones  at  the  surface  and  destroying 
the  bond.  The  detritus  is  deposited  on  the  side  of  the  road,  and 
subsequently  removed  in  carts  or  wagons. 

383.  The  mud  is  usually  removed  from  broken-stone  roads  in 
the  cities,  but  not  from  rural  highways.  In  those  localities  where 
the  soil  is  sticky,  as  for  example  in  the  prairie  regions  of  Illinois 
and  Iowa,  keeping  the  crushed  stone  free  from  mud  is  a  serious 
problem,  particularly  if  most  of  the  side  roads  are  unpaved.     Fur- 

.ther,  certain  somewhat  unscientific  attempts  at  road  building  in 
such  localities  seem  to  show  that  serious  difficulties  may  be  en- 
countered by  the  road  surface's  being  picked  to  pieces  by  the 
adhesion  of  the  mud.  It  is  a  serious  question  whether  broken-stone 
roads  can  be  built  in  such  localities  with  sufficient  binding  power 
to  resist  the  adhesive  action  of  the  mud. 

384.  Drainage.  At  any  season  of  the  year  anything  that  im- 
pedes the  free  discharge  of  the  rain  water  from  the  surface  should 
receive  careful  attention.  Water  lodging  in  a  depression  should 
not  be  drained  off  by  a  trench  to  the  side  of  the  roadway,  but  the 
hole  should  be  filled  up  (§  378);  and  the  gutters  should  be  kept  free 
from  mud  and  rubbish.  In  the  fall,  all  weeds  and  grass  in  the 
ditches  should  be  cut  and  removed,  and  the  culverts  and  outlets 
should  be  left  free  and  open.  All  ditches  and  culverts  should  be 
inspected  in  advance  of  the  spring  rains;  and  in  northern  localities 
where  snow  lies  for  considerable  time,  the  outlets  of  all  water 
courses  should  be  opened  before  the  spring  thaw  sets  in. 

385.  Patching.  If  the  road  is  maintained  in  good  repair,  there 
will  be  no  deep  holes  or  ruts,  but  only  shallow  depressions  or  slack 
places  which  show  where  fresh  material  should  be  applied.  These 
depressions  are  deepest  at  the  center  and  gradually  grow  shallower 


ART.  3.]  MAINTENANCE.  253 

toward  the  edges.  Care  is  required  in  determining  the  size  and 
shape  of  the  patches  of  stone  to  be  spread  in  these  hollows.  In- 
experienced workmen  are  inclined  to  lay  stones  in  rectangular 
patches,  with  more  regard  to  the  neat  appearance  of  the  newly 
spread  stone  than  to  the  needs  of  the  road,  and  thus  parts  of  round 
or  oval-shaped  hollows  are  left  uncovered,  or  stone  is  spread  where 
it  is  not  required.  The  angles  of  a  square  patch  are  very  liable  to 
be  knocked  away;  and  even  if  the  stones  are  not  wasted  in  this 
way,  they  do  not  set  as  quickly  as  if  laid  in  a  round  form.  If  the 
ends  of  a  patch  be  made  in  the  form  of  an  oval,  more  or  less  pointed, 
the  traffic  will  gradually  work  over  it  from  the  sides;  and  on  a 
hill  the  water  will  be  diverted  towards  the  sides  of  the  road  instead 
of  running  into  the  stone,  as  it  does  with  a  square-ended  patch. 
Care  should  be  taken  to  cover  the  whole  surface  of  the  depression 
so  as  to  leave  no  place  where  water  may  lodge;  and  the  depression 
should  be  filled  full  enough  so  that  after  consolidation  of  the  sur- 
face, the  patch  will  conform  to  the  original  cross  section  of  the  road. 
If  the  hole  is  not  filled  full  enough,  it  will  soon  appear  again  in  the 
same  place ;  and  if  it  is  filled  too  full,  other  depressions  will  form 
on  each  side  of  the  patch. 

If  from  neglect  or  bad  management,  long  ruts  or  large  hollows 
have  been  allowed  to  form,  they  should  be  repaired  in  short  lengths 
and  one  part  at  a  time.  Horses  avoid  long  strips  of  stones  laid  in 
a  hollow  worn  by  wheels,  and  soon  make  another  rut  alongside. 
Laying  a  long  strip  of  materials  on  the  middle  of  the  road  diverts 
the  traffic  to  the  sides,  which  are  sure  to  suffer  a  good  deal  and  may 
be  entirely  cut  up  before  the  stones  in  the  middle  are  compacted. 
To  avoid  retarding  the  travel  and  increasing  the  draft  too  much, 
a  new  coat  should  not  be  put  on  any  continuous  space  larger  than 
5  or  6  square  yards.  If  several  depressions  are  found  very  near 
each  other,  fill  the  worst  and  attend  to  the  next  after  the  first  has 
become  solid. 

The  stone  employed  in  patching  should  be  a  little  smaller  than 
that  of  which  the  road  was  originally  constructed ;  and  should  never 
be  applied  in  a  thick  coat.  A  layer  one-stone  thick  after  consolida- 
tion is  enough;  and  if  the  stones  are  sufficiently  close  to  support 
each  other,  such  a  course  will  bond  well.  If  one  such  coat  is  not 
enough,  a  second  may  be  added  when  the  first  is  nearly  consolidated. 


254  BROKEN-STONE    ROADS.  [CHAP.   V. 

Ordinarily,  in  applying  patches  in  thin  coats  over  small  areas 
it  is  unnecessary  to  use  binding  material,  since  the  road  usually 
has  enough  detritus  to  fill  the  interstices  of  the  new  stone.  If  laid 
in  damp  weather,  when  the  surface  of  the  road  is  soft,  there  is 
usually  no  difficulty  in  getting  a  layer  one  stone  thick  to  consoli- 
date without  any  binding  material.  If  the  surface  is  very  compact, 
or  if  the  new  stone  is  very  hard,  it  may  be  wise  to  loosen  the  old 
surface  around  the  edge  of  the  patch  with  a  pick,  and  also  to  scrape 
the  detritus  from  the  surface  of  the  road  and  apply  it  to  the  edge 
of  the  patch.  In  extreme  cases,  it  may  be  necessary  to  add  a 
binding  material.  Screenings,  or  sand  with  considerable  clay  will 
greatly  facilitate  binding;  and  after  the  traffic  has  forced  the 
surplus  clay  to  the  surface,  it  can  be  scraped  off.  Such  a  patch 
will  finally  become  firm  and  hard. 

If  the  patch  is  small  and  thin,  it  will  usually  be  thoroughly 
consolidated  by  the  traffic;  but  if  it  is  thick,  it  may  be  necessary 
to  tamp  it.  However,  as  a  rule,  it  is  much  better  to  lay  succes- 
sively two  thin  courses  than  one  thick  one. 

386.  The  method  of  continuous  maintenance  is  a  method  of 
constant  patching.  This  method  contemplates  restoring  to  the 
whole  length  of  the  road  an  amount  of  stone  equal  to  the  annual 
loss  by  wear,  and  therefore  it  is  necessary  to  do  more  than  just  fill 
the  holes  and  depressions  as  described  in  the  preceding  section. 

In  maintaining  the  road  by  patching,  it  is  impracticable  to 
employ  a  roller,  and  therefore  the  patches  must  be  put  on  in  such 
a  manner  as  to  induce  travel  to  consolidate  the  new  stone.  The 
method  of  accomplishing  this  is  as  follows :  The  first  patches  are 
made  along  the  middle  of  the  road  at  intervals  of  about  50  yards, 
without  reference  to  any  depressions  that  there  may  be  between. 
These  patches  have  the  shape  of  elongated  rectangles,  about 
3X8  feet.  The  whole  section  having  been  gone  over  in  this  way, 
the  roadman  commences  again  at  the  original  starting-point  and 
makes  new  patches,  checker-board  fashion,  alternately  on  the 
right  and  the  left  of  the  first  patches  and  midway  in  the  space 
between  them.  On  the  third  trip,  he  makes  new  patches  be- 
tween the  second  set;  and  so  on,  always  observing  the  checker- 
board arrangement.  Thus  in  five  trips  the  whole  central  part  of 
the  roadway  has  been  covered,  while  travel  has  been  induced  to 


ART.  3.] 


MAINTENANCE. 


255 


change  direction  five  times  and  virtually  to  pass  over  nearly  the 
whole  surface. 

387.  Re-surfacing.  The  term  re-surfacing  is  frequently  applied 
to  two  distinct  operations.  One  consists  in  smoothing  and  leveling 
up  the  surface  of  an  old  road  without  adding  much,  if  any,  new 
material;  and  the  other  consists  in  adding  an  entirely  new  layer 
of  material  to  an  old  road.  For  greater  clearness,  the  first  will 
here  be  called  re-grading,  and  the  second  re-coating. 

388.  Re-grading.  When  the  surface  of  the  road  has  become 
uneven  and  rough,  and  when  the  broken  stone  is  thick  enough 
not  to  require  much  new  material,  the  top  of  the  road  is  loosened, 
re-graded,  and  re-rolled.  The  loosening  is  usually  done  by  run- 
ning over  the  road,  one  or  more  times,  with  a  steam  stone-road 
roller  having  spikes  in  the  rear  wheels — see   Fig.   66.  Of   course 


Fig.  66.— Steam  Roller  Spiking  Old  Broken-Stone  Road. 

the  roller  must  be  heavy  enough  to  force  the  spikes  into  the 
road  metal;  but  to  insure  this  condition  the  size  of  the  spikes  is 
usually  thus  adjusted  to  the  weight  of  the  roller.  The  amount  of 
rolling  required  depends  upon  the  hardness  of  the  road  and  the 
amount  of  hand  labor  used;  in  one  case  a  12-ton  roller  loosened  240 


256  BROKEN-STONE    ROADS.  [CHAP.  V. 

square  yards  of  a  hard  limestone  per  hour.*  The  spikes  break  up 
the  layer  to  a  depth  of  3  or  4  inches,  after  which  men  complete  the 
loosening  process  by  breaking  up  the  larger  masses  with  hand 
picks.  Sometimes  the  old  road  is  broken  up  by  a  plow  drawn  by 
a  steam  roller;  but  ordinarily  this  is  not  as  good  as  using  the  spikes 
on  the  roller,  since  the  road  is  not  broken  up  to  a  uniform  depth, 
and  since  there  is  danger  of  mixing  the  under-material  with  the 
top  course,  thus  rendering  the  latter  unfit  for  use  again.  Some- 
times a  harrow  follows  the  plow  or  the  roller. 

After  the  crust  is  broken  up,  the  surface  is  leveled  off  by  the 
use  of  shovels  and  rakes;  and  then  it  is  sprinkled  and  rolled  as  in 
the  original  construction.  Usually  no  new  binding  material  is  re  * 
quired,  the  detritus  from  the  old  road  being  sufficient. 

The  following  tabular  statement  shows  the  distribution  of  tha 
labor  and  the  cost  of  re-grading  a  limestone  road  having  an  ex- 
ceedingly hard  crust:* 

Loosening  with  roller  @,  $1.00  per  hour 0.4  cents  per  sq.  yd. 

Picking  by  hand  @.  20  cents  per  hour 1.2      "        "    "     " 

Re-spreading  @  20  cents  per  hour 0.8      "        "    "     " 

Rolling  ©  $1.00  per  hour 0.33    "        "     "  '" 

Sprinkling  with  cart  @  40  cents  per  hour 0.13"        "     "    " 

Foreman — 143  hours  for  9,400  sq.  yds.  @  30  cents 

per  hour 0.44   "        "     "    « 

Total  cost  of  re-grading  3.30   "        "     "    " 

Re-grading  is  applicable  only  when  the  road  wears  unexpect- 
edly rough  and  uneven,  or  when  the  road  was  originally  made 
needlessly  thick.  It  is  not  economical  to  spend  time  and  money 
in  consolidating  a  thick  layer  part  of  which  must  later  be  loosened 
and  re-consolidated.  True  economy  requires  the  construction 
of  a  road  of  such  a  thickness  that  when  the  surface  is  too  rough 
and  uneven  for  further  service,  the  road  will  be  worn  so  thin  as  to 
require  a  layer  of  new  material — which  should  be  added  without 
materially  disturbing  the  old  surface;  that  is,  it  is  more  economical 
to  construct  a  thin  road  and  give  it  a  new  top  as  occasion  may  re- 
quire, than  it  is  to  build  a  thick  road  and  re-grade  it  one  or  more 
times  before  it  is  worn  so  thin  as  to  require  a  new  top  layer. 

389.  Re-coating.     All  dust  or  mud  should  be  removed  from  the 

*  Engineer  in  j  News,  Vol.  45,  p.  411. 


ART.  3.]  MAINTENANCE.  257 

old  surface  before  adding  the  new  material.  Where  the  surface 
of  the  old  road  is  very  compact  and  the  new  material  is  hard  and 
tough,  it  may  be  necessary  to  loosen  the  surface  with  picks  to  the 
depth  of  \  an  inch,  to  secure  a  good  bond  between  the  old  surface 
and  the  new  material;  but  usually  it  is  sufficient  to  score  the  sur- 
face with  a  hand  pick,  making  gashes  8  to  12  inches  apart,  having 
a  maximum  depth  of  }  of  an  inch.  If  the  sides  of  the  road  need  no 
new  material,  a  shallow  groove  having  its  outer  face  vertical 
should  be  cut  longitudinally  along  the  edge  of  the  portion  to  be 
covered,  so  as  to  form  a  buttress  for  the  new  top  and  to  secure  a 
good  union  of  the  old  and  the  new  material.  Where  water  is  plen- 
tiful, it  is  wise  to  soften  the  surface  by  copious  sprinkling,  to 
insure  a  firm  bond  between  the  new  material  and  the  old  road-bed. 
The  new  stone  is  to  be  spread,  rolled,  and  sprinkled  just  as  in  new 
construction. 

The  cost  of  labor  to  lay  21,908  square  yards  of  a  3-inch  course 
of  2-inch  trap  rock,  bound  with  trap  screenings,  in  New  York 
City  in  1897  was  as  follows:* 

Scraping  and  sweeping 2 .  00  cents  per  sq.  yd. 

Picking  old  surface   1 .50      "        "     "    "" 

Spreading  stone 2.00      "        "     "    " 

Rolling  (47.15  sq.  yd.  per  hour) 2.76      "        "     "     " 

Total  cost  of  labor  in  re-coating 8 .26     "        "     "     " 

390.  COST  OF  MAINTENANCE.  The  cost  of  maintenance  varies 
greatly  with  the  quality  and  cost  of  the  stone  used,  the  amount  of 
travel  per  unit  of  width,  the  climatic  conditions,  the  cost  of  labor, 
the  length  of  time  considered,  and  the  state  in  which  the  road 
is  maintained;  and  consequently  any  general  data  are  liable 
to  be  misleading  when  applied  to  a  particular  case. 

There  are  almost  no  valuable  data  concerning  the  cost  of 
maintaining  American  broken-stone  roads.  The  Reports  of  the 
Massachusetts  Highway  Commission  for  1900  and  for  1901  give 
definite  information  concerning  the  expenditures  for  repairs  on 
state-aid  road;  but  these  data,  although  frequently  quoted,  are 
without  general  significance,  since  all  of  the  roads  are  compara- 
tively new,  being  from  1  to  5  years  old,  and  the  expense  for  the 

*  Trans.  Amer.  Soc.  of  Civil  Engineers,  Vol.  41, .p.  127. 


258  BROKEtf-STOtfE    ROADS.  [CHAP.  V. 

different  ages  is  not  separated,  and  since  the  roads  are  in  widely- 
separated  sections  varying  from  £  to  5  miles  in  length,  and  further 
since  a  considerable  part  of  the  expenditure  for  maintenance  was 
for  the  purchase  of  sufficient  repair  stone  to  last  for  several  years. 
"The  cost  of  maintenance,  which  was  about  equally  distributed 
over  the  roadway  and  the  roadside,  consisted  of  cutting  brush 
and  weeds,  cleaning  waterways  and  gutters  to  permit  a,  free  flow 
of  water,  trimming  down  the  shoulders,  cutting  small  waterways 
through  them,  and  filling  washouts."  The  roads  are  maintained 
by  the  continuous  repair  system;  and  as  soon  as  the  length  of  any 
one  section  will  justify,  the  road  is  to  be  put  under  the  care  of  a 
man  constantly  in  attendance.* 

Michigan  Boulevard,  Chicago,  a  50-foot  granite  macadam 
driveway  from  which  heavy  traffic  teams  are  excluded  but  which 
has  a  very  large  travel,  costs  for  maintenance  per  annum  as  follows :  f 

Sprinkling 4.9  cents  per  sq.  yd. 

Sweeping  and  removing  manure 7.8      "        "     "     " 

Patching  here  and  there 0.6      "        "     """ 

Re-coating  surface 15 .0      "        "     "     " 

Total  annual  cost  of  maintenance 28 .3      "       "    "     " 

This  is  a  city  street  under  the  control  of  the  South  Park  Commis- 
sioners, and  is  continuously  maintained  in  a  first-class  condition. 

Driveways  in  the  South  Side  Parks,  Chicago,  40  feet  wide,  with 
a  crushed  limestone  surface,  cost  as  follows  per  year  for  main- 
tenance :  t 

Sprinkling 4.8  cents  per  sq.  yd. 

Sweeping  and  removing  manure 3.0      "        "     "     " 

Patching  here  and  there 0.5      *       "     "     " 

Re-coating  surface 1.7      "       "     "     " 

Total  annual  cost  of  maintenance 10.0      "        "     "     " 

In  the  Boston  Parks,  the  annual  cost  of   repairs  of  a  telford 

crushed-stone  road  was  $198.00  per  mile,  of  which  $129.00  was  for 

stone  screenings,  $49.00  for  teaming,  and  $20.00  for  labor.    The 

sprinkling  cost  $721.00  per  mile,  of  which  the  water  cost  $187.00 

(16  cents  per  1,000  gallons),  and  the  teaming  $533.00.J 

*  Report  of  Massachusetts  Highway  Commission  for  1901,  p.  22-23. 

f  J.  F.  Foster,  Superintendent  and  Engineer  of  South  Park  Commissioners. 

%  Jour.  Association  of  Engineering  Societies,  Vol.  10,  p.  235. 


ART.  3.] 


MAINTENANCE. 


259 


39.1.  In  France,  elaborate  and  carefully  analyzed  accounts 
are  kept  of  the  cost  of  maintaining  the  public  highways;  but 
owing  to  differences  in  the  climatic  conditions  and  the  prices  of 
labor,  and  also  owing  to  variations  in  the  character  of  the  road 
metal,  such  data  are  valuable  only  for  the  particular  locality. 

There  are  321,812  miles  of  stone  roads  in  France,  which  is 
equivalent  to  1  mile  of  road  for  each  0.66  square  mile  of  area  or  1.52 
miles  of  road  per  square  mile,  and  to  1  mile  of  road  for  each  119 
inhabitants.  The  average  cost  of  maintenance  per  mile  is  about 
$223.00  per  square  mile  of  area,  and  about  $1.39  per  inhabitant. 
Table  26,  gives  a  summary  of  the  annual  expenditures  for 
material  and  labor  for  the  roadway  proper.  To  obtain  the 
total  cost  of  maintenance,  add  about  45  per  cent  to  the  results  in 
Table  22  to  cover  expenditures  for  water  courses,  sidewalks,  plant- 
ing of  trees,  and  general  administration. 

TABLE  26. 
Outlay  for  Materials  and  Labor  on  the  Roadway  Proper  in  France.* 


Class  of  Road. 

Length, 
Miles. 

Annual  Cost  of  Maintenance. 

Ref. 
No. 

Total. 

Per  Mile. 

1 

National  roads...  . 

22  009 

16  188 

128  522 

155  093 

$4  333  500f 
2  794  723t 

15  835  100J 
8  488  537J 

$225.00 

2 

County  roads 

172 

3 

Township  roads 

123 

4 

Neighborhood  roads 

Total 

55 

321  812 

31  551  860 

$98.05 

*  Rockwell's  Roads  and  Pavements  in  France,  p.  67. 

f  For  1893.  %  Average  for  threo  years,  1886-88. 

The  followixig  are  some  of  the  details  of  the  cost  of  maintain- 
ing the  National  Roads  of  France  during  1893 : 

Number  of  miles 22  009 

Average  travel  in  24  hours,  "units"  (see  §  373) . . 170.6 

"        amount  of  broken  stone  required  (including  7£  per  cent  of 

binding  gravel)  per  mile  per  100  "units,"  cubic  yards 49. 

"        quality  of  stone,  i.e.,  average  coefficient  of  wear  (§  282) ....  10.85 

"        cost  of  stone,  per  cubic  yard $1.17 

"  "     "  binding  gravel,  per  cubic  yard $0.36 

"        labor  cost  per  mile  per  100  " units" $30 . 71 

"  "        "      "    cubic  yard  of  material  used $0.63 

"        wages  of  roadman  per  day $0 .  55 

"        cost  per  mile  per  100  " units"  for  materials $58 . 75 

"  "      "      "      "    100        "         "   labor $30.71 

Total  average  cost  per  mile  per  100  "units"  for  material  and  labor  $89 .46 


260  BROKEN-STOKE   ROADS.  [CHAP.  V. 

In  the  Department  of  Havre,  France,  the  average  annual  cost 
of  sweeping,  removing  mud,  watering,  and  maintaining  all  works 
is  as  follows:  for  departmental  roads  in  the  cities  3.0  cents  per 
square  yard,  and  in  the  country  1.8  cents,  and  for  communal  roads 
1.1  cents  per  square  yard.* 

392.  ECONOMICS  OF  THE  STONE  ROAD.  For  a  few  remarks 
on  the  advantage  of  a- permanently  hard  road  surface,  see  §  265, 
page  172,  which  statements  concerning  gravel  roads  apply  with 
equal  force  to  stone  roads. 

There  is  a  certain  financial  advantage  in  a  crushed-stone  road, 
but  whether  its  construction  will  be  true  economy  is  a  problem 
that  can  be  solved,  even  approximately,  only  for  each  individual 
case.  The  solution  of  the  problem  requires  the  correct  determina- 
tion of  the  following  items:  the  cost  of  construction  of  the  new 
road,  the  cost  of  maintenance  for  the  old  road  and  also  for  the  new, 
the  cost  of  transportation  oh  the  old  and  the  new  road,  the  amount 
of  traffic  both  before  and  after  the  improvement,  and  the  rate  of 
interest.  To  illustrate  the  method  of  using  such  data,  an  example 
will  be  assumed. 

It  is  assumed  (1)  that  the  cost  of  construction  is  $5,000.00  per 
mile;  (2)  that  the  annual  interest  is  5  per  cent;  (3)  that  the  annual 
traffic  is  5,000  tons  in  full  loads;  (4)  that  the  average  cost  of  main- 
tenance of  the  present  earth  road  is  $40.00  per  annum;  (5)  that 
the  annual  cost  of  maintaining  the  proposed  stone  road  is  $200.00 
per  annum;  (6)  that  the  cost  of  transportation  in  full  loads  on  the 
present  earth  road  is  15  cents  per  ton  mile;  (7)  that  the  cost  of 
transportation  on  the  proposed  stone  road  is  5  cents  per  ton  mile. 
The  account  would  then  stand  about  as  follows :  The  annual  cost 
of  a  mile  of  the  stone  road  is  equal  to  the  interest  on  $5,000  at  5 
per  cent  or  $250  plus  the  difference  in  cost  of  maintenance  ($200  — 
$40)  =  $160;  and  the  total  cost  is  $250  +  $160  =  $410.  The  annual 
saving  by  the  stone  road  is  10  cents  per  ton  mile  on  5,000  tons,  or 
$500  per  annum.  This  example  shows  a  saving  of  $90  (  =  $500 
—  $410)  per  annum  per  mile  by  the  construction  of  the  stone  road. 
In  connection  with  the  above  computation  the  following  limiting 
conditions  should  be  remembered : 

*  Specif!  U.  S.  Consular  Reports  on  Streets  and  Highways  in  Foreign  Countries, 
p.  71. 


AKT.   3.]  MAINTENANCE.  261 

1.  The  cost  of  the  stone  surface  will  depend  upon  the  locality, 
the  width  of  the  road,  and  the  character  of  the  construction.  Con- 
siderable expense  may  be  required  to  reduce  the  grades;  for  unless 
the  grades  of  stone  roads  are  light,  the  cost  of  transportation  is  not 
much  less  than  that  on  an  earth  road.  The  cost  of  construction 
should  include  the  cost  of  building  new  bridges  or  of  strengthening 
old  ones,  to  permit  the  passage  of  the  heavier  loads  incident  to 
the  economic  use  of  the  stone  road. 

2.  Five  per  cent  interest  is  too  small  for  some  localities,  but 
is  too  great  for  many  communities;  and  it  may  reasonably  be 
assumed  that  in  the  future  interest  rates  will  gradually  decrease. 
The  lower  the  interest  the  better  the  opportunity  to  secure  im- 
proved roads.  If  the  road  is  to  be  financially  profitable,  the  orig- 
inal cost  must  be  considered  a  business  investment  which  will  pay 
dividends. 

3.  In  considering  the  financial  value  of  the  proposed  improve- 
ment, only  full  loads  should  be  included  in  computing  the  saving 
in  cost  of  transportation;  but  in  any  probable  case  there  will  also 
be  a  miscellaneous  traffic  which  will  be  benefited  by  the  better  road. 
The  benefit  to  any  but  full  loads  will  be  chiefly  in  the  saving  of  time ; 
but  the  value  of  this  saving  can  not  be  computed,  since  it  will 
depend  upon  the  value  of  small  fractions  of  time  for  other 
purposes. 

4.  The  cost  of  maintenance  of  the  present  earth  road  and  also 
of  the  proposed  stone  one  should  include  the  periodic  repairs  or 
renewals  of  bridges  and  culverts. 

5.  The  cost  of  maintenance  of  the  stone  road  should  include 
not  only  the  cost  of  petty  repairs  during  the  first  few  years  of  the 
life  of  the  road,  but  also  the  cost  of  periodically  renewing  the 
surface.  The  cost  of  maintenance  will  vary  with  the  climatic  con- 
ditions, the  nature  of  the  soil,  the  character  of  the  road  material, 
the  amount  of  traffic,  the  price  of  labor,  etc. 

6.  The  cost  of  transportation  on  either  the  earth  or  the  stone 
road  depends  upon  whether  it  is  done  by  a  freighter  or  a  farmer 
(see  §  4-7),  and  also  upon  the  climate,  the  nature  of  the  soil,  the 
grades,  etc. 

7.  If  the  hauling  is  done  upon  wagons  used  chiefly  in  general 
farm  work  or  upon  earth  roads,  the  capacity  of  the  wagon  will  limit 


262  BR0KEX-ST0NE    ROADS.  [CHAP.  Y. 

the  load,  and  hence  the  full  economic  advantage  of  the  hard  road 
surface  can  not  be  secured. 

Further,  there  is  some  financial  advantage  in  being  able  to  use 
the  roads  at  any  season  of  the  year,  but  such  an  advantage  can  not 
be  computed  for  a  general  case  nor  usually  in  a  particular  case. 
Finally,  there  is  a  social  advantage  in  permanently  good  roads 
(see  §  .1)  that  should  not  be  overlooked  in  considering  any  pro- 
posed road  improvement. 


CHAPTER  VI. 
MISCELLANEOUS  ROADS. 

393.  WHEELWAYS.  When  wheeled  vehicles  are  drawn  by- 
horses,  the  wheels  should  move  on  the  smoothest  and  hardest 
surface  possible,  while  the  horses  require  a  surface  rough  enough 
to  give  them  a  secure  foothold  and  soft  enough  to  be  easy  to  their 
feet.  The  two  opposite  requirements  are  united  only  in  wheel- 
ways,  i.  e.,  in  roads  in  which  two  parallel  rails  of  suitable  material 
are  provided  to  receive  the  wheels,  while  the  space  between  the 
rails  is  filled  with  a  different  material,  on  which  the  horses  travel. 
In  ancient  times,  stone  wheelways  were  of  considerable  impor- 
tance; and  because  of  this,  and  of  the  frequent  proposals  now-a- 
days  to  build  wheelways  of  steel  and  burned  clay,  this  class  of 
roadways  will  be  briefly  considered. 

394.  Stone  Wheelways.  The  Egyptians  seem  first  to  have 
discovered  the  value  of  stone  wheelways.  In  modern  times  they 
have  been  used  in  London  and  other  European  cities,  but  appar- 
ently have  been  abandoned  save  in  northern  Italy. 

Telford  made  an  ingenious  use  of  wheelways  on  his  Holyhead 
road  (third  paragraph  of  §  304).  Two  hills,  each  a  mile  in  length, 
had  an  inclination  of  1  in  20.  To  reduce  the  grades  to  1  in  24 
would  have  cost  $100,000.  Nearly  the  same  advantage  in  dimin- 
ishing the  tractive  force  was  obtained  by  moderate  cutting  and 
embanking  and  by  making  stone  wheelways,  at  a  total  expense  of 
less  than  half  the  amount  the  grading  would  have  cost.  The 
construction  was  as  follows:  "The  blocks  were  of  granite,  12 
inches  deep,  14  inches  wide,  and  not  less  than  4  leet  long.  A  foun- 
dation for  them  was  prepared  by  making  an  excavation  8  feet  wide 
and  25  inches  deep.  On  its  leveled  bottom  was  laid  a  telford  pave- 
ment (§  302)  8  inches  deep,  the  interstices  being  filled  with  gravel. 

263 


264  MISCELLANEOUS  KOADS.  [CHAP.  VI. 

Upon  this  pavement  were  laid  3  inches  of  broken  stones,  none 
exceeding  1^  inches  in  their  longest  dimensions.  On  these  stones 
was  a  layer  of  2  inches  of  the  best  gravel,  over  which  a  heavy  roller 
was  passed.  Upon  this  the  stone  blocks  or  trams  were  laid  to 
a  very  accurate  level.  On  each  side  of  the  blocks  was  placed  a 
row  of  paving-stones  of  granite,  6  inches  deep,  5  inches  wide,  and 
9  inches  long.  The  remaining  space  between  and  outside  of  the 
lines  of  paving  stones  was  filled  up  with  hard  broken  stone,  and  the 
whole  was  covered  with  a  top  dressing  of  one  inch  of  good  gravel." 

395.  Steel  Wheelways.  In  recent  years  there  have  been  many 
proposals  to  build  steel  wheelways.  Numerous  designs  have  been 
offered  for  the  rail,  most  of  which  are  highly  impracticable,  being 
difficult  to  manufacture,  to  lay,  and  to  maintain.  A  number  of 
the  rails  would  require  the  construction  of  expensive  machinery 
for  their  manufacture  before  they  could  be  tried  even  experi- 
mentally. Three  or  four  sections  from  16  to  180  feet  long  have 
been  built,  and  for  a  time  were  exploited  in  the  newspapers;  but 
even  a  little  experience  with  them  showed  that  they  were  prac- 
tically worthless.  A  short  section  well  cared  for  on  dry  ground 
under  an  experimental  wagon  gives  little  or  no  indication  of  the 
result  under  the  ordinary  conditions  of  actual  service. 

Apparently  the  first  steel  wheelway  was  constructed  in  Spain 
in  1892  from  Valencia  to  Grao — a  distance  of  two  miles.  Valencia 
has  a  population  of  about  170,000  and  Grao  is  the  seaport.  The 
■  road  is  a  double  track,  and  the  space  between  the  rails  and  adja- 
cent to  them  is  paved  with  stone  blocks.  The  rail  consists  of  two 
inverted  trough  sections  bolted  together,*  and  apparently  simply 
embedded  in  the  sand.  The  cost,  including  the  paving,  was  $7,665 
per  mile  of  single  track.  The  traffic  is  said  to  be  3,200  vehicles  a 
day.  The  cost  of  maintaining  the  former  macadam  surface  was 
$5,470  per  annum;  and  since  the  opening  of  the  steel  wheelway, 
the  cost  of  maintenance  is  said  to  be  but  $380  a  year.  For  several 
reasons,  this  example  is  not  a  very  valuable  guide  for  American 
practice. 

396.  The  only  practical  test  of  a  steel  wheelway  ever  made 
in  this  country  was  upon  a  section  built  in  Chicago  in  1901  from 

*For  detailed  illustration,  see  Engineering  News,  Vol.  42,  p.  367. 


WHEELWAYS. 


265 


designs  prepared  in  the  Office  of  Road  Inquiry  of  the  U.  S.  Agri- 
cultural Department.     Fig.  67  shows  the  cross  section  proposed 


!i  i  !    i! 

It   i 


4-r 

5-6k" 


I . 


Broken  Stone  Wei/ Rol/cd 


■i— '  i  J 


Broken  Sfone 


5-5" 


&7/7#  /Te//  /fo//«/ 


Broken  Sfone 


Fig.  67.— Cross  Section  of  Steel  Wheelway. 

for  the  road,  and  Fig.  68  shows  the  details  of  the  rail.  The  two 
rails  are  tied  together  by  a  2|Xj-»nch  bar  riveted  to  two  short 
pieces  of  4x3X-rVmcn  angles  which  are  bolted  to  the  inside 
and  the  outside  flanges  of  each  rail.  These  gage-ties  are  spaced 
15  feet  apart.  The  rails  are  spliced  end  to  end  by  the  breaking  of 
the  joints  of  the  several  members  composing  a  wheelway.  Owing 
to  the  impossibility  of  filling  the  underside  of  the  rail  with  concrete, 


Cross  Section  of  Rail.  Detail  of  Tie  Cor?r?ectior? 

Fig.  68.— Details  op  Steel  Wheelway. 

the  road  was  not  built  according  to  the  cross  section  shown  in  Fig. 
67;  and  consequently  the  rail  was  filled  with  a  2"X8"  pine 
timber.  About  2,100  feet  of  double  track  was  laid  where  the  traffic 
was  exceptionally  heavy.  This  traffic  consisted  chiefly  of  wagons 
heavily  laden  with  packing-house  products.  The  rails  were  em- 
bedded in  crushed  limestone,  and  the  space  between  them  was  filled 
with  the  same  material.  The  work  was  done  under  the  direction 
of  a  competent  railroad  engineer. 

Within  two  or  three  weeks  after  completion,  the  following 
defects  had  appeared:  1.  The  inner  edge  of  the  rails  was  con- 
siderably depressed,  owing  to  the  compression  of  the  crushed 
stone  under  the  rail.     2.  The  face  of  the  rail  was  concave  except 


266  MISCELLANEOUS    EOADS.  [CHAP.   VI. 

where  the  gage-ties  were  attached,  owing  to  the  compression  of 
the  wood  under  the  rail  and  to  the  spreading  apart  of  the  lower  edges 
of  the  rail.  3.  The  rails  were  bowed  horizontally  outward,  between 
the  gage-ties,  owing  to  the  wedging  action  of  the  crushed  stone 
between  the  rails.  4.  Pieces  of  broken  stone  were  continually 
loosened  by  the  horses'  feet  and  kicked  upon  the  face  of  the  rail, 
where  they  were  ground  to  powder. 

At  this  stage,  sawed  railroad  ties  were  inserted  3  feet  apart, 
and  both  flanges  of  the  rails  were  spiked  to  the  ties.  After  these 
repairs,  the  rails  maintained  their  position  reasonably  well,  but 
deflected  between  the  ties;  and  bad  ruts  soon  formed  adjacent 
to  the  rails,  and  the  crushed  stone  was  ground  up  to  such  an  extent 
that  the  rail  was  almost  hidden  by  dust.  It  is  conceded  that  this 
steel  wheelway  has  not  been  a  success.     It  has  been  taken  up. 

397.  Advantage  of  Steel  Wheelways.  The  chief  advantage 
claimed  for  the  steel  wheelway  is  a  reduction  of  traction  and  a 
consequent  permissible  increase  of  the  load.  The  advocates  of 
this  form  of  roadway  frequently  compare  the  tractive  resistance 
per  ton  on  earth  roads  with  that  on  railroads,  and  conclude  that 
a  horse  can  draw  ten  to  twenty  times  as  much  on  a  steel  wheelway 
as  upon  an  earth  road.  This  conclusion  is  erroneous  for  two 
reasons:  1.  The  steel  wheelway  advocated  is  not  anything  like 
as  rigid  and  smooth  as  the  ordinary  railroad  track,  nor  can  it  be 
kept  nearly  as  clean.  A  thin  film  of  dirt  on  the  rail  materially 
increases  the  tractive  power — compare  lines  16  and  17  of  Table  8, 
page  29.  2.  In  the  above  claim  as  to  the  relative  loads  upon  a  steel 
wheelway  and  an  earth  road  the  effect  of  the  footing  upon  the  load 
a  horse  can  draw  is  not  considered.  Unless  the  space  between  the 
rails  is  paved,  a  steel  wheelway  would  be  but  little  better  than 
an  earth  road  in  a  muddy  time — when  the  advantages  of  a  steel 
wheelway  are  most  desired.  Further,  unless  the  space  between 
the  rails  is  paved,  it  will  be  impossible  for  vehicles  to  turn  on  or 
off  the  wheelway  except  at  specified  points.  If  turnouts  are  fre- 
quent, the  expense  will  be  great;  and  if  they  are  infrequent  the 
inconvenience  will  be  great.  Therefore,  it  is  safe  to  assume  that 
any  successful  wheelway  must  have  a  permanently  hard  surface 
between  the  rails;  and  consequently  the  tractive  resistance  of  a 
wheelway  should  be  compared;  not  with  an  earth  road    but  with 


WHEELWAYS.  267 


a  road  having  the  same  surface  as  that  between  the  rails  of  the 
wheehvay. 

Tests  made  by  the  author  on  the  steel  wheelway  described  in 
§  396  (see  Table  8,  page  29)  show  that  the  tractive  resistance 
of  such  a  road  under  the  most  favorable  condition  is  more  than 
that  of  a  good  brick  or  macadam  surface ;  and  that  under  ordinary 
conditions  it  is  about  the  same  as  that  of  a  new  plank  road,  or  an 
ordinary  brick  pavement  with  concrete  foundation,  or  a  specially 
dressed  granite-block  pavement.  The  force  of  traction  on  the 
steel  wheelway  is  surprisingly  large,  and  is  doubtless  due  to  the 
deflection  of  the  rail  as  a  whole  and  also  of  its  surface  immediately 
under  the  wheel,  the  wheel  being  continually  compelled  to  climb 
a  grade.  In  the  light  of  these  tests,  it  must  be  concluded  that 
unless  the  rail  is  very  rigid  and  is  kept  clean,  the  reduction  of  trac- 
tive power  will  not  be  very  great.  If  the  wheelwTay  is  made  rigid, 
the  cost  of  construction  will  be  considerably  increased;  and  if  the 
rail  is  to  be  kept  clean,  the  space  between  the  rails  and  adjacent 
to  them  must  be  covered  with  a  practically  indestructible  surface 
which  must  be  frequently  swept. 

In  considering  the  relative  tractive  power  required  on  different 
road  surfaces,  it  should  not  be  forgotten  that  the  disadvantages 
of  a  grade  increase  as  the  tractive  resistance  decreases.  For  ex- 
ample, if  on  a  steel  wheelway  the  resistance  is  20  pounds  a  ton ,  a 
1  per  cent  grade  will  double  the  resistance;  while  on  a  macadam 
road  having  a  tractive  resistance  of  40  pounds  a  ton,  a  1  per  cent 
grade  will  increase  the  resistance  only  one  half;  and  if  the  tractive 
force  required  on  the  macadam  is  80  pounds  a  ton,  a  1  per  cent 
grade  will  increase  the  resistance  only  one  fourth.  In  other  words, 
in  the  above  illustration  a  horse  on  a  steel  wheelway  can  draw 
only  half  as  much  up  a  1  per  cent  grade  as  on  a  level,  while  on  the 
first  macadam  road  he  can  draw  two  thirds  and  on  the  second  eight 
tenths  as  much  up  the  1  per  cent  grade  as  on  the  level.  There- 
fore the  advantage  of  steel  wheelways  in  decreasing  the  force 
cf  traction  can  be  obtained  only  when  the  wheelway  is  level  or 
nearly  so. 

398.  It  is  sometimes  claimed  that  a  steel  wheelway  makes  a 
very  durable  road.  As  far  as  the  steel  rails  are  concerned,  this 
is  true;  but  it  is  not  true  of  the  surface  adjoining  the  rails — what- 


258  MISCELLANEOUS  ROADS.  [CHAP.  VI. 

ever  that  surface.  It  is  often  assumed  that  the  space  adjoining 
the  steel  rails  is  to  be  paved  with  crushed  stone.  If  this  is  done, 
vehicles  in  turning  out  to  pass  each  other  will  certainly  wear  ruts 
adjoining  the  rails,  as  is  shown  by  the  ruts  worn  in  the  most  durable 
pavements  by  vehicles  turning  on  and  off  of  street-car  rails.  Fur- 
ther, it  is  well  known  that  tracking  is  one  of  the  most  effective 
causes  of  the  destruction  of  crushed-stone  roads,  partly  because 
the  stones  loosened  by  the  horses'  feet  are  not  rolled  into  place 
by  the  wheels ;  and  consequently  the  horses'  feet  will  be  more  destruc- 
tive on  a  macadamized  steel  wheel  way  than  on  an  ordinary  crushed  - 
stone  road.  It  has  been  estimated  (§  372)  that  the  wear  of  ordi- 
nary macadamized  roads  due  to  the  horses'  feet  is  1 J  to  3  times  as 
much  as  that  due  to  the  wheels.  In  consideration  of  the  tendency 
of  the  wheels  to  produce  ruts  adjacent  to  the  rails,  and  of  the 
failure  of  the  wheels  to  roll  into  place  the  stones  loosened  by  the 
horses'  feet,  it  is  probable  that  a  steel  wheelway  will  at  best  add 
nothing  to  the  durability  of  the  adjoining  macadam. 

If  the  space  between  the  rails  is  paved  with  a  more  durable 
material  than  macadam,  the  cost  will  be  unreasonably  great. 
The  question  of  cost  will  be  considered  in  the  next  section. 
/  399.  Disadvantages  of  Steel  Wheelway s.  The  most  serious  ob- 
jection to  a  steel  wheelway  is  that  if  it  does  not  have  a  perma- 
nent footway  for  the  horses  it  is  least  effective  in  a  muddy  time, 
i.  e.,  when  most  needed;  and  if  it  does  have  a  permanently  hard 
surface  between  the  rails,  the  cost  is  unreasonable. 

If  a  steel  wheelway  is  laid  in  a  crushed-stone  road,  the  additional 
cost  will  be  (1)  the  cost  of  the  metal,  (2)  the  cost  of  placing  the 
metal,  including  the  increased  cost  of  compacting  the  crushed  stone, 
and  (3)  the  increased  cost  of  maintenance. 

1.  The  steel  wheelway  shown  in  Fig.  67  and  68,  page  265,  will 
require  about  121  tons  of  steel  for  a  mile  of  single  track.  The 
cost,  delivered,  would  probably  not  be  less  than  $40  a  ton,  in  which 
case  the  metal  for  a  mile  of  single  track  will  cost  $4840.  In  this 
connection  it  should  not  be  forgotten  that  experience  with  the 
above  described  steel  wheelway  shows  that  the  rails  are  too  light 
for  any  considerable  traffic. 

2.  The  cost  of  placing  the  metal  will  vary  considerably  with  the 
design  of   the  track  and  with   the  thoroughness  with  which  the 


WHEELWAYS.  269 


stone  is  compacted  around  the  rails.  Only  practical  experience 
can  determine  how  much  labor  will  be  required  to  form  an  even 
bed  for  the  rails,  to  bolt  together  the  rails  and  attach  the  gage-ties, 
and  to  consolidate  the  stone  around  the  rails  and  the  ties,  but  it 
would  probably  amount  to  at  least  $500  per  mile.  There  are  14,000 
feet  of  lumber  in  a  mile  of  single  track  like  that  shown  in  Fig.  67, 
which  in  place  will  cost  at  least  $25  per  thousand  feet,  or  $350 
a  mile.  If  concrete  is  employed,  it  will  cost  two  or  three  times 
as  much  as  the  lumber.  The  total  cost  of  placing  the  metal  will 
thus  be  at  least  $850  a  mile  of  single  track. 

3.  It  is  impossible  accurately  to  estimate  the  cost  of  mainte- 
nance. Only  experience  can  determine  the  amount  of  labor  re- 
quired to  prevent  low  joints  and  to  fill  up  the  horse  paths  and  the 
ruts  next  to  the  rails.  However,  it  seems  reasonable  to  estimate 
that  these  expenses  will  amount  at  least  to  as  much  as  the  main- 
tenance of  an  ordinary  crushed-stone  road  to  carry  the  same  traffic; 
and  hence  in  this  comparison  such  expense  may  be  neglected. 

The  total  cost  of  the  wheelway  proper  would  then  be  $4,840 
+  $850  =  $5,690  a  mile  over  and  above  the  cost  of  a  crushed-stone 
road.  What  are  the  advantages  to  be  derived  from  this  expendi- 
ture? Only  the  possibility  of  a  slight  decrease  in  the  tractive  power. 
In  considering  the  effect  of  this  decrease,  it  should  be  remem- 
bered that  it  is  of  value  only  to  fully  loaded  teams;  and,  further, 
that  such  an  advantage  would  accrue  only  to  such  fully  loaded 
teams  as  haul  their  load  from  start  to  finish  upon  the  steel  wheel- 
way  or  other  equally  good  road.  The  above  cost  would  then  be 
incurred  for  a  very  slight  advantage  to  a  very  small  part  of  the 
traffic,  and  therefore  there  are  few  circumstances  under  which 
the  cost  of  a  steel  wheelway  would  be  justifiable. 

400.  A  single-track  wheelway  is  undesirable,  since  vehicles 
must  turn  out  frequently  in  meeting  each  other,  and  since  either 
the  slowest  team  will  regulate  the  speed  of  the  procession  or  the 
faster  teams  must  turn  out  and  go  around.  Turning  out  is  diffi- 
cult on  account  of  the  flange  on  the  rail;  and,  further,  the  sliding 
of  a  wheel  against  the  flange  causes  the  opposite  wheel  to  tear  up 
the  macadam  surface.  A  double -track  wheelway  would  only 
partially  remove  the  above  objections;  and  ordinarily  where 
there  is  traffic  enough  to  justify  a  double-track  wheelway,  a  uni- 


270  MISCELLANEOUS    ROADS.  [CHAP.   VI. 

versal  wheelway,  i.  e.,  a  first-class  pavement,  should  be  built.  On  the 
double-track  steel  wheelway  described  in  §  396,  more  than  half  of 
the  vehicles  turned  out  and  went  around  the  slow  ones. 

401.  Another  objection  to  any  wheelway  is  that  owing  to  the 
comparatively  narrow  space  between  the  rails,  the  horses  are 
compelled  frequently  to  step  upon  the  rails,  the  smooth  surface 
of  which  interferes  with  the  footing  of  the  horses.  This  in  a  con- 
siderable measure  neutralizes  the  advantage  of  a  smooth  track 
for  the  wheels.  Teamsters  using  the  steel  wheelway  described  in 
§  396  strongly  urged  this  objection,  and  in  addition  claimed  that 
the  projecting  flange  injured  the  frog  of  the  horse's  foot. 

402.  Still  another  objection  to  a  wheelway  is  that  the  gage 
of  vehicles  varies  considerably,  and  consequently  either  the  face  of 
the  rail  must  be  very  wide — a  requirement  which  adds  expense, — 
or  some  vehicles  can  not  be  accommodated.  In  almost  any  large 
city,  wagons  are  found  with  gages  varying  from  4  feet  8  inches 
to  6  feet. 

403.  The  conclusion  is  that  trackways  are  out  of  date;  that 
they  are  more  expensive  and  less  effective  than  good  macadam 
roads;  and  that  for  a  country  road  where  an  ordinary  macadam 
surface  does  not  suffice,  a  first  class  pavement  or  a  railroad  should 
be  built. 

404.  Clay-block  Wheelway.  It  has  frequently  been  proposed 
to  build  a  wheelway  of  burned  clay  blocks.  After  the  above  dis- 
cussion of  steel  wheelways,  little  need  be  said  concerning  this 
form.  The  blocks  proposed  are  usually  comparatively  small, 
and  would  probably  be  difficult  to  place  and  to  keep  in  line,  par- 
ticularly during  freezing  and  thawing  weather;  they  would  prob- 
ably lack  durability ;  and  the  cost  of  such  construction  would  prob- 
ably be  unreasonably  great.  The  wheelway  referred  to  in  §  394 
was  built  by  an  accomplished  road  builder  where  such  roads  were 
common,  and  therefore  the  construction  was  presumably  suited 
to  the  service;  and  if  this  be  true,  no  cheaply  constructed  wheel- 
way  can  render  efficient  service. 

405.  BURNED-CLAY  ROADS.  In  the  Mississippi  Valley,  where 
gravel  or  rock  suitable  for  ballast  must  be  transported  consid- 
erable distances,  the  railroads  have  been  experimenting  in  recent 
years  with  burned-clay  ballast,  and  it  has  frequently  been  proposed 


BURNED-CLAY    ROADS.  271 


to  use  that  material  instead  of  crushed  stone  for  building  wagon 
roads. 

Almost  any  clay,  except  one  containing  considerable  sand, 
can  be  used  for  this  purpose;  but  one  containing  considerable 
organic  matter,  though  it  burns  more  easily  and  is  lighter  to  handle, 
gives  a  more  friable  product.  The  so-called  gumbo  soil  is  much 
used  for  burned-clay  ballast.  The  best  clay  for  this  purpose  is 
usually  found  in  bottom  lands,  and  is  distinguished  by  being 
very  plastic,  very  fine  grained,  and  quite  tenacious — in  its  native 
condition,  the  very  worst  material  of  which  to  build  a  wagon  road. 
The  burning  is  done  in  ridges  often  2,000  to  4,000  feet  long,  the 
clay  being  mixed  with  nut  or  slack  coal.  As  a  rule,  the  better 
grades  of  coal  are  more  satisfactory,  since  the  fire  burns  better 
and  is  not  so  likely  to  be  put  out  by  rains.  Wood  is  used  to  start 
the  fire.  The  railroads  usually  locate  the  kiln  alongside  of  a  track, 
and  handle  the  material  almost  entirely  by  steam  power.  The 
clay  is  loosened  by  a  plow  attached  to  a  locomotive,  and  falls  upon 
a  conveyor  which  elevates  it  to  the  ridge-like  kiln.  The  coal  is 
shoveled  directly  from  the  cars  upon  the  kiln.  Successive  layers  of 
clay  and  coal  are  added  on  one  side  of  the  ridge,  while  on  the  other 
side  the  burned  clay  is  allowed  to  cool.  In  this  way  the  pit  ad- 
vances sidewise  a  few  feet  each  day.  About  1,000  cubic  yards  a 
day  can  be  burned  in  a  kiln  4,000  feet  long,  50  men  and  a  locomo- 
tive being  required  to  do  the  work.* 

The  cost  of  burning  depends  upon  the  weather,  the  cost  of  coal, 
and  the  facilities  for  draining  the  kiln.  Under  favorable  condi- 
tions, a  ton  of  coal  will  burn  4  to  6  cubic  yards  of  clay.  The  cost 
of  burned  clay  when  burned  as  above  varies  from  75  cents  to  $1.00 
a  cubic  yard  on  board  cars.  The  labor  cost  exclusive  of  train 
service  is  about  50  cents  a  cubic  yard. 

406.  The  burned  clay  or  gumbo  used  by  railroads  for  ballast 
is  a  reddish,  gravelly  material,  the  fragments  of  which  are  angular, 
very  porous,  and  usually  about  as  hard  as  soft  burned  brick.  The 
chief  merit  of  this  material  for  railroad  ballast  is  its  porosity — 
just  the  opposite  of  the  quality  desired  for  the  surface  of  a  wagon 
road.     It  is  not  known  that  this  material  has  been  tried  for  wagon 


*  Engineering  News,  Vol.  30,  p.  399-400. 


272  MISCELLANEOUS   ROADS.  [CHAP.  VI. 

roads,  but  it  will  probably  prove  to  be  too  soft  and  friable,  and 
too  deficient  in  binding  power  (§  277).  The  localities  in  which 
clay  suitable  for  burning  is  available,  are  those  having  a  very  sticky 
soil,  which,  when  carried  upon  the  road,  would  probably  speedily 
pull  to  pieces  even  the  best  stone  roads.  In  several  respects  the 
conditions  necessary  for  the  successful  use  of  burned  clay  as  rail- 
road ballast  are  very  different  from  those  required  for  its  economic 
use  as  a  surfacing  material  for  wagon  roads ;  and  it  is  at  least  doubt- 
ful whether  fragments  of  burned  clay  will  ever  come  into  consider- 
able use  for  wagon  roads  in  any  locality. 

It  is  possible  that  clay  burned  as  brick  may  be  employed  for 
country  roads  where  there  is  a  scarcity  of  gravel  or  suitable  stone, 
in  which  case  the  road  will  be  constructed  practically  as  a  brick 
pavement — see  Chapter  XIV.  The  advantage  of  a  brick  road- 
way over  one  made  of  fragments  of  burned  clay  is  that  with  the 
former  the  clay  can  be  burned  more  thoroughly,  more  uniformly, 
and  more  economically  in  a  permanent  kiln  than  in  a  temporary 
pit;  and  bricks  are  of  a  better  form  for  road  building  than  irreg- 
ular fragments. 

407.  CONCRETE  ROADS.  Concrete  is  much  used  for  the  founda- 
tion of  pavements  (see  Art.  2,  Chapter  XII),  and  in  a  few  cases  it 
has  been  used  for  the  wearing  surface.  In  Philadelphia  many 
alleys  are  paved  with  hydraulic  cement  concrete,  in  which  case 
it  is  laid  as  for  sidewalks  (§  933-57);  and  in  several  cities  where 
asphalt  or  some  of  its  substitutes  have  been  used  for  a  wearing 
surface  on  a  foundation  of  concrete,  when  the  surface  coat  has 
worn  out  the  traffic  has  been  allowed  to  come  directly  upon  the 
concrete  foundation. 

This  form  of  road  surface  is  not  likely  to  come  into  general  use 
owing  to  its  cost  and  slipperiness  when  laid  as  are  sidewalks,  and  its 
cost  and  lack  of  durability  when  laid  like  the  foundation  of  a  pave- 
ment. Portland  cement  concrete  is  said  to  be  used  in  preference 
to  all  other  paving  materials  in  Grenoble,  France,  and  in  several 
German  cities,  but  such  use  must  be  under  exceptional  conditions. 

408.  For  a  consideration  of  tar-concrete  and  tar-macadam 
roads,  see  §  698-713. 

409.  SHELL  ROADS.  Around  the  Chesapeake  Bay  and  on  the 
coast  of  the  Gulf  of  Mexico,  oyster  shells  have  been  used  to  a 


SLAG    ROAD.  273 


considerable  extent  for  road  purposes.  They  are  spread  loosely 
over  the  road  and  speedily  become  consolidated  by  the  traffic. 
The  shells  have  a  high  cementing  power,  but  a  very  low  resistance 
to  crushing;  and  while  they  make  a  smooth  road  surface,  it  is 
speedily  ground  to  powder,  producing  a  disagreeable  dust,  and 
requiring  the  constant  application  of  new  shells  to  keep  it  from 
rutting.     A  shell  road  is  suitable  only  for  light  driving. 

At  many  points  along  the  Atlantic  and  Gulf  coast-lines,  there 
are,  under  the  mud  flats  and  marshes,  extensive  beds  of  ancient 
oyster  shells,  which  may  be  easily  excavated  and  made  available 
for  road-building  purposes.*  In  localities  where  the  traffic  is  not 
heavy  and  where  gravel  or  stone  suitable  for  road  coverings  can 
not  be  procured  except  at  considerable  cost  for  transportation, 
oyster  shells,  either  ancient  or  modern,  afford  a  fairly  good  and 
cheap  road-building  material. 

On  the  shores  of  the  Chesapeake  Bay  it  is  common  to  build 
these  roads  18  feet  wide,  the  loose  shells  being  18  inches  deep  in 
the  center  and  9  inches  on  the  sides.  The  shells  cost  about  2  cents 
a  bushel,  making  the  total  cost  of  the  road  about  $1,740  per  mile 
(16^  cents  per  sq.  yd.).  Shells  are  used  for  paving  in  a  number 
of  cities  of  the  Gulf  coast,  and  such  pavements  often  cost  50  to 
70  cents  a  square  yard. 

410.  SLAG  ROAD.  Blast-furnace  slag  from  old-style  iron 
furnaces  has  a  glassy  appearance,  is  very  hard  and  brittle,  and 
except  for  foundations  is  of  little  value  as  a  road  material,  since 
it  quickly  grinds  to  fine  dust.  The  slag  from  modern  steel  fur- 
naces is  comparatively  light,  has  a  sponge-like  structure,  and  con- 
tains a  large  amount  of  lime.  When  used  for  roads  this  variety 
compacts  very  readily  and  forms  an  even  and  hard  surface.  Steel- 
furnace  slag  dust  has  a  high  cementing  power. 

Slag  is  used  for  road  purposes  only  to  a  limited  extent,  and 
only  near  steel  mills. 

411.  COAL-SLACK  ROADS.  Coal  slack  is  sometimes  used  for 
road  building  where  neither  stone  nor  gravel  is  available  at  reason- 
able cost.  The  slack  is  friable  and  easily  grinds  to  powder,  but 
makes  a  fair  road  for  light  traffic.     In  many  localities  the  large 

*  Professor  Shaler  in  Fifteenth  Annual  U.  S.  Geological  Report,  1893-94,  p.  287. 


274  MISCELLANEOUS   ROADS.  [CHAP.   VI. 

quantities  of  slack  are  a  burden,  and  could  profitably  be  spread 
upon  the  roads.     It  is  light,  and  therefore  easily  hauled. 

412.  PLANK  ROADS.  Plank  roads  were  once  somewhat 
common  in  the  heavily  timbered  portion  of  the  northern  United 
States  and  of  Canada.  The  first  plank  road  on  this  continent  was 
built  in  Canada  in  1836.  These  roads  are  practicable  only  where 
timber  is  plentiful  and  cheap,  where  stone  or  gravel  is  scarce  and 
expensive,  and  where  there  is  little  or  no  water  or  rail  transporta- 
tion and  consequently  a  great  demand  upon  wagon  roads.  Only 
a  few  plank  roads  are  now  in  existence,  but  such  roads  have  been 
advantageous  in  the  development  of  a  new  country. 

Plank  roads  are  usually  about  8  feet  wide,  and  occupy  one  side 
of  an  ordinary  earth  road,  the  other  side  being  used  to  turn  out 
upon  and  for  travel  during  the  dry  season.  The  method  of  con- 
struction most  commonly  followed  is  to  lay  down  lengthwise  of 
the  road,  two  parallel  rows  of  plank  called  sleepers  or  stringers, 
about  5  feet  apart  between  centers,  and  upon  these  to  lay  cross- 
planks  3  to  4  inches  thick  and  8  feet  long.  The  ends  of  the  planks 
are  not  adjusted  to  a  line,  but  form  short  offsets  at  intervals  of 
2  to  3  feet,  to  prevent  the  formation  of  long  ruts  at  the  edges  of 
the  road,  and  to  aid  vehicles  in  regaining  the  plank  covering  in 
turning  onto  the  road.  The  planks  were  often  covered  with  gravel, 
sand,  or  loam  to  protect  them  from  wear. 

When  kept  in  repair,  plank  roads  make  a  comparatively  smooth 
roadway  possessing  some  advantages  for  both  heavy  and  light 
traffic,  but  the  planks  are  very  likely  to  be  displaced — even  when 
spiked  down  as  was  sometimes  done, — and  are  also  likely  to  be 
floated  away.  Being  alternately  wet  and  dry,  the  plank  rotted 
rapidly,  and  at  best  did  not  last  more  than  five  years,  and  some- 
times only  two. 

Most  plank  roads  were  toll  roads,  and  often  paid  a  handsome 
profit  to  their  owners. 

413.  CORDUROY  ROADS.  Corduroy  roads  are  make  shifts  em- 
ployed in  a  new  timbered-country  to  carry  a  road  over  a  swamp 
or  marsh  which  can  not  be  drained  without  undue  expense.  They 
are  built  by  laying  logs  side  by  side  across  the  roadway,  the  spaces 
between  the  larger  poles  being  leveled  up  with  smaller  ones.  With 
sufficient  care,  such  roads  can  be  made  fairly  smooth  when  new; 


CHARCOAL   ROADS.  275 


but  they  are  usually  exceedingly  rough,  and  grow  worse  with  age. 
Although  corduroy  roads  afford  means  of  crossing  swamps  which 
at  times  are  otherwise  utterly  impassable,  their  retention  upon 
a  road  of  any  considerable  travel  is  usually  unjustifiable. 

414.  CHARCOAL  ROADS.  Where  timber  was  very  plentiful 
and  gravel  scarce,  a  fair  road  for  light  traffic  has  been  made  by 
felling  and  burning  the  timber,  and  covering  the  road  with  the 
charcoal.  Poles  from  6  to  16  inches  in  diameter  are  piled  length- 
wise in  the  center  of  the  road — 5  feet  high,  9  feet  wide  at  the  base, 
and  2  feet  on  top — and  covered  with  straw  and  earth.  The  earth 
required  to  cover  the  timber  is  taken  from  the  side  ditches.  When 
charred,  the  earth  and  charcoal  are  spread  over  a  width  of  15  feet, 
leaving  it  2  feet  thick  at  the  center  and  1  foot  at  the  sides,  al- 
though a  depth  of  15  inches  at  the  center  and  10  inches  at  the  side 
makes  a  fairly  good  road. 

The  charcoal  is  soft  and  friable,  and  hence  should  be  covered 
with  a  thin  layer  of  gravel  for  greater  durability,  and  to  prevent 
it  from  blowing  and  washing  away,  or  from  catching  fire  from 
matches  or  lighted  cigars  thrown  upon  the  surface.  The  earth 
covering  of  the  charcoal  pit  is  a  fair  road  material  and  may  be 
used  as  a  top-dressing  for  the  charcoal. 

Charcoal  roads  cost  from  $500  to  $1,500  per  mile,  and  of  course 
are  feasible  only  when  the  timber  has  no  market  value,  and  must 
be  got  rid  of  before  the  land  can  be  devoted  to  agricultural  purposes. 


CHAPTER  VII. 
EQUESTRIAN   ROADS  AND  HORSE-RACE  TRACKS. 

416.  The  prime  object  in  the  construction  of  ordinary  roads 
is  to  secure  a  firm  unyielding  surface  that  will  give  a  low  tractive 
resistance  and  be  durable  and  easy  to  maintain;  while  in  the  class 
of  roads  to  be  considered  in  this  chapter,  the  chief  purpose  is  to 
secure  a  road  that  shall  be  easy  on  the  horse  and  enable  him  to 
attain  a  high  speed. 

Art.  1.    Equestrian  Roads. 

417.  Equestrian  Roads  or  Saddle  Paths  are  ways  designed 
especially  for  horse-back  riding. 

418.  WIDTH  AND  CROWN.  Equestrian  roads  are  seldom  made 
narrower  than  12  feet,  and  in  populous  districts  are  often  20  to 
30  feet  wide.  The  crown  of  the  narrower  road  is  about  3  inches 
and  of  the  wider  6  inches.  The  material  of  the  surface  being  light 
and  loose,  the  grade  both  transverse  and  longitudinal  should  be 
slight,  as  otherwise  there  is  danger  of  the  surface  being  badly 
washed. 

419.  DRAINAGE.  On  the  ordinary  road  or  pavement,  the 
surface  is  compact  and  acts  as  a  roof  to  shed  the  rain  water  into 
the  side  ditches;  but  on  an  equestrian  road,  the  surface  is  loose 
and  absorbent,  and  therefore  the  drainage  of  the  road-bed  is  even 
more  important  than  that  of  an  ordinary  road  or  pavement. 

The  ground  should  have  thorough  underdrainage — either  nat- 
ural or  artificial.  Since  the  surface  of  the  road  must  be  loose 
and  porous,  it  can  not  have  any  considerable  transverse  slope  for 
fear  the  surface  material  will  be  washed  away;  and  therefore 
to   facilitate  the  drainage,  the  subgrade  should  be  crowned.     In 

276 


ART.   1.]  EQUESTRIAN    ROADS.  277 

constructing  a  wide  bridle  path,  it  may  be  necessary  to  form  the 
subgrade  and  lay  tile  as  shown  in  Fig.  69;   but  ordinarily  this 


Form  of  Subgrade  of  a  Wide  Equestrian  Road. 


is  not  required,  one  of  the  constructions  described  below  being 
sufficient. 

If  the  soil  is  a  close  retentive  clay,  a  regular  telford  foundation 
or  a  layer  of  rubble  should  be  placed  on  the  subgrade.  The  latter 
was  employed  in  the  riding  paths  of  Central  Park,  New  York  City, 
with  entire  satisfaction.  A  layer  of  3  or  4  inches  of  clean  coarse 
gravel  should  be  placed  upon  the  telford  or  rubble  foundation, 
to  prevent  the  surfacing  from  working  into  the  foundation. 

If  the  soil  is  somewhat  porous,  the  telford  or  rubble  founda- 
tion is  not  required;  and  then  the  layer  of  gravel  is  placed  directly 
upon  the  subgrade,  to  aid  the  drainage  and  to  keep  the  fine  surface 
material  from  becoming  mixed  with  the  soil  below. 

420.  SURFACE.  Since  no  vehicular  traffic  is  to  be  provided  for, 
a  smooth  hard  surface  is  not  required;  but  it  is  necessary  that 
the  surface  shall  be  somewhat  soft  and  loose,  so  as  to  protect  the 
horse  from  injury  and  to  make  the  riding  easy  and  agreeable.  The 
surface  must  be  such  as  not  to  become  greatly  impaired  during 
wet  weather  nor  be  subject  to  material  changes  in  dry  weather, 
and  not  be  acted  upon  by  frost.  It  should  be  neither  too  rigid  nor 
too  yielding,  but  should  be  of  such  consistency  as  to  afford  the 
easiest  movement  of  horse  and  rider,  and  at  the  same  time  be 
reasonably  durable  and  economical  to  repair  and  maintain.  Loam, 
sand  and  clay,  gravel,  and  tan  bark  have  been  used.  Loam  would 
probably  be  most  suitable,  if  it  could  be  maintained  at  all  times 
in  its  best  condition.  In  the  South  Side  Parks  of  Chicago,  ordi- 
nary black  earth  laid  on  a  sandy  subsoil  and  covered  with  a  thin 
dressing  of  detritus  from  macadam  and  gravel  roads  gives  very 
satisfactory  results,  although  the  roads  become  soft  in  very  wet 
weather. 

Ordinarily  equestrian  roads  are  surfaced  with  2  to  3  inches 
of  coarse  sand  or  fine  gravel  practically  free  from  earthy  matter, 


278  EQUESTRIAN  ROADS  AND  HORSE-RACE  TRACKS.    [CHAP.  VII. 

After  being  spread  evenly  with  rakes,  it  is  lightly  sprinkled  and 
then  rolled  with  a  light  roller  just  enough  to  keep  the  horses'  feet 
from  sinking  into  it.  If  the  surface  has  a  tendency  to  pack  too 
hard  under  use,  a  little  clean  coarse  sand  strewn  over  the  surface 
will  counteract  it;  and  on  the  other  hand,  if  the  surface  is  too 
loose  and  yielding,  the  addition  of  a  small  quantity  of  clay  or  loam 
with  sprinkling  and  rolling  will  correct  the  defect. 

Art.  2.     Horse-race  Tracks. 

421.  An  engineer  is  occasionally  required  to  lay  out  and  con- 
struct a  horse-race  track,  and  therefore  a  consideration  of  this 
subject  is  not  out  of  place  here. 

422.  THE  FORM.  The  best  form  for  speed  would  be  a  straight 
level  track,  since  on  it  every  exertion  of  power  by  the  horse  would 
be  employed  in  producing  speed;  but  such  a  form  is  objectionable, 
since  the  start  and  finish  can  not  be  observed  by  the  same  spec- 
tators nor  be  timed  by  the  same  judges.  If  the  track  is  curved, 
centrifugal  force  is  developed;  and  unless  the  speed  corresponds 
exactly  to  the  super-elevation  of  the  outside  of  the  track,  i.  e.. 
to  the  transverse  slope  of  the  surface,  part  of  the  exertion  of  the 
horse  will  be  consumed  in  overcoming  centrifugal  force,  and  con- 
sequently the  maximum  speed  will  not  be  attained.  If  the  race 
is  side  by  side,  centrifugal  force  is  of  no  great  consequence ;  but 
where  the  race  is  for  a  record  or  against  time,  it  is  important 
to  have  every  condition  favorable, — especially  when  seconds  are 
divided  into  fifths. 

The  intensity  of  centrifugal  force  varies  inversely  as  the  radius 
of  curvature  and  directly  as  the  speed;  and  therefore  to  secure  a 
minimum  effect  of  centrifugal  force  the  amount  of  curvature  should 
be  as  small  as  possible,  and  the  radius  of  curvature  should  be  as 
large  as  possible.  The  fastest  track  that  permits  the  race  to  ter- 
minate near  the  starting  point,  is  two  straight  lines  crossing  each 
other  at  an  angle  and  being  connected  at  one  extremity  by  a  cir- 
cular arc  of  long  radius,  since  this  track  gives  a  large  radius  and 
minimum  curvature.  This  form  is  known  as  a  kite  track  (see 
§  427).  The  next  best  form  is  an  oval,  on  which  the  races  begin 
and  end  at  the  same  point.     An  oval  contains  360°  of  curvature* 


ART.  2.] 


flORSE-RACE   TRACKS. 


279 


while  a  kite  track  of  the  same  length  has  considerably  less  curva- 
ture. The  most  unfavorable  condition  for  speed  is  one  or  more 
times  around  a  small  oval  or  circle. 

The  kite-shaped  track  requires  more  ground  than  the  oval, 
does  not  afford  the  spectators  quite  as  good  a  view  of  the  race, 
and  does  not  permit  races  longer  than  once  around  the  track.  The 
half-mile  oval  requires  less  ground  than  the  mile  oval,  gives  the 
spectators  a  better  view  of  the  race,  and  is  favorable  for  races 
longer  than  once  around  the  track.  A  circular  track  is  not  so  good 
as  an  oval,  since  a  straight  stretch  is-  desirable  for  the  start  and 
finish.  Half-mile  oval  tracks  are  most  common,  mile  ovals  are 
next,  and  kite  tracks  are  least  common.  Straight  tracks  are  con- 
structed only  for  fast  pleasure  driving,  when  they  are  usually 
termed  speedways. 

423.  The  usual  forms  of  tracks  and  the  methods  employed  in 
laying  them  out  will  be  described,  and  then  some  designs  by  the 
author  will  be  presented. 

424.  Standard  Oval.  Mile  Track.  Fig.  70  shows  the  usual 
form  of  the  mile  oval,  the  only  variation  being  in  the  width 
of  the  track  itself.  The  dotted  line  represents  the  pole  line, 
the  line  upon  which  the  distance  is  measured,  which  is  univer- 
sally 3  feet  outside  of  the  inner  edge  of   the  track.      The  wire 


■r-*v 


4 


-3ft 


/32otf       ^ 


*40ft 


J 


feC 


6S.ff: 


* 


132m 


s^aafcak 


:3J: 


Fig.  70.— Standard  Oval  Mile  Track. 


is   usually  300  feet   from    the  beginning   of  the  curve,    A.     The 
i,  i,  and  f   mile  points   are   indicated  by  poles  set  at  the  inside 


280  EQUESTRIAN-  EOADS  AND  HORSE-RACE  TRACKS.    [CHAP.  VII. 

edge  of  the  track,  in  such  a  position  that  a  line  from  the  judges' 
stand  cuts  the  pole  line  at  the  proper  point. 

In  constructing  the  track,  it  is  more  convenient  to  mark  the 
inner  edge  of  the  track  than  the  pole  line.  The  semi-circular 
ends  may  be  laid  out  by  any  of  three  methods : 

1.  Amateur's  Method.  Fasten  one  end  of  a  wire  of  a  length 
equal  to  the  radius,  at  the  center  of  the  semi-circle,  and  swing  the 
free  end  around  and  establish  as  many  points  on  the  inside  edge 
of  the  track  as  are  desired.  A  wire  is  better  than  a  string  or  rope, 
since  it  will  stretch  less. 

2.  Surveyor's  Method.  Establish  eight  points  in  each  quad- 
rant by  laying  off  the  lines  and  distances  shown  in  Fig.  71.    This 


Fio.  71.— Surveyor's  Method  for  Mile  Track. 


method  gives  points  on  the  curve  about  66  feet  apart,  and  is  de- 
signed especially  for  the  land  surveyor,  wTho  ordinarily  uses  a  66- 
foot  chain  or  steel  tape. 

3.  Engineer's  Method.  Set  a  transit  at  the  tangent  point  (A, 
Fig.  72),  and  lay  off  successively  the  equal  angles  au  a2,  a3,  etc., 
as  shown  in  Fig.  72,  and  measure,  also  successively,  the  equal 
chords  A  E,  E  F,  FG,  etc.  The  angle  a  may  have  any  value,  pro- 
vided the  length  of  the  chord  is  made  to  correspond;  but  for  con- 
venience, a  should  be  an  aliquot  part  of  90°.  Table  27,  page  281, 
gives  several  values  of  a  and  the  corresponding  values  of  the  chord 
and  also  of  the  arc. 


ART.   2.] 


HORSE-RACE    TRACKS. 


281 


425.  The  outside  edge  of  the  track  need  not  be  laid  out  accu- 
rately. It  is  sufficient  to  set  a  flag  pole  at  the  center  of  the  semi- 
circle and  measure  from  the  inside  edge  in  the  line  of  the  radius. 
The  track  shown  in  Fig.  70,  i.  e.,  the  standard  mile  track  having 


i 


Fig.  72.— Engineer's  Method  of  Laying  Out  Curve. 

a  home-stretch  65  feet  wide  and  the  remainder  40  feet  wide,  re^ 
quires  a  rectangle  of  ground  2,240  X  945  feet,  or  about  48.5  acres, 
for  the  track  alone. 

TABLE  27. 
Deflection  Angles  and  Chords  for  Standard  Oval  Mile  Track. 


Ref. 
No. 

Deflection  Angle. 

Length  of  the 
Chord. 

Length  of  the  Arc. 

Number  of 

Points  on  the 

Semi-circle. 

1 

1  io 

21.84  ft. 

21.84  ft. 

60 

2 

2° 

29.12  " 

29.12  " 

45 

3 

2|° 

36.39  " 

36.40  " 

36 

4 

3° 

43.67  " 

43.69  " 

30 

5 

H° 

65.46  " 

65.53  " 

20 

6 

5° 

72.72  " 

72.81  " 

18 

7 

6° 

87.21  " 

87.37  " 

15 

8 

7i° 

108.90  " 

109.21  " 

12 

426.  Half-mile  Track.  Fig.  73,  page  282,  shows  the  usual 
half-mile  oval,  the  only  variation  being  in  the  width  of  the  track. 
The  dotted  line  represents  the  pole  line,  the  line  upon  which 
the  distance  is  measured,  and  is  always  3  feet  outside  of  the  inner 
edge  of  the  track.    The  wire  is  usually  170  feet  from  the  beginning 


282 


EQUESTRIAN"  ROADS  AND  HORSE-RACE  TRACKS.    [CHAP.  VII. 


of  the  curve.     The  semi-circular  ends  may  be  laid  off  in  any  of 
three  ways : 


Fig.  73— Standard  Half-mile  Oval  Track. 

1.  Amateur' s  Method.  Fasten  one  end  of  a  wire  of  a  length 
equal  to  the  radius,  at  the  center  of  the  curve,  and  with  the  other 
mark  as  many  points  as  desired  on  the  inside  edge  of  the  track. 

2.  Surveyor's  Method.  Establish  five  points  by  laying  off  the 
lines  and  distances  shown  in  Fig.  74. 


Fig.  74.— Surveyor's  Method  for  Half-mile  Track. 

3.  Engineer's  Method.  Set  a  transit  at  the  tangent  point  (A. 
Fig.  72,  page  281),  and  lay  off  successively  the  equal  angles  at,  a2,  a3. 
etc.,  and  the  equal  chords  A  E,E F,F  G,  etc.,  as  shown  in  Fig.  72. 


ART.   2.] 


HORSE-RACE    TRACKS. 


283 


Table  28  gives  various   deflection  angles   and  the   corresponding 
chords,  any  pair  of  which  may  be  employed. 

TABLE  28. 
Deflection  Angles  and  Chords  for  Standard  Half-mile  Track. 


Ref. 
No. 

Deflection  Angle. 

Length  of  the 
Chord. 

Length  of  the  Arc. 

Number  of 

Points  on  the 

Semi-circle. 

1 

3° 

21.68  ft. 

21.69  ft. 

30 

2 

<H° 

32.50  " 

32.53  " 

20 

3 

5° 

36.10  " 

36.14  " 

18 

4 

6° 

43.29  " 

43.37  " 

15 

5 

7i° 

54.06  " 

54.21  " 

12 

6 

9° 

64.79  " 

65.06  " 

10 

The  track  shown  in  Fig.  73,  i.  e.,  the  standard  half-mile  oval 
with  a  home-stretch  65  feet  wide  and  the  remainder  40  feet  wide, 
requires  a  rectangle  of  ground  1,160X525  feet,  or  practically 
14  acres  for  the  track  alone. 

427.  Kite  Track.      Fig.    75    shows    the  form    of    kite    track 


Start-'    "Uucfges'Stancf 
Fig 


r5.— Kite  Track. 


introduced  at  Independence,  Iowa,  in  1890.  The  larger  circular 
end  may  be  laid  out  with  a  wire  used  as  a  radius,  or  by  the 
measurement  of  the  lines  shown  in  Fig.  76;  but  for  somewhat  ob- 
vious reasons,  the  method  described  in  the  succeeding  paragraph 
is  the  best. 

The  curve  could  be  laid  out  by  setting  off  equal  deflection  angles 
an$  measuring  the  corresponding  chords  as  was  explained  in  para- 
graphs 3  of  §  424  and  §  426;  but  in  this  case  the  central  angle  con- 
tains fractional  degrees,  and  hence  the  deflection  angle  would  be 


284  EQUESTRIAN  ROADS  AND  HORSE-RACE  TRACKS.    [CHAP.  VII. 

inconvenient  both  to  compute  and  to  set  off  on  the  instrument. 
Therefore  it  is  better  to  lay  cut  the  curve  by  the  method  usually 
employed  for  railroad  curves,  i.  e.,  by  successive  100-foot  chords 
with  a  fractional  chord  at  the  end.  The  degree  of  the  curve  is 
12°  V  47" ',  and  hence  the  deflection  angle  for  a  100-foot  chord  is 
6°  0'  53"  or  practically  6°  1'.  The  arc  for  a  100-foot  chord  is 
100.183  feet,  and  hence  the  number  of  100-foot  chords  is  17.4580 
(  =  1,749-^100.183);  in  other  words,  there  will  be  seventeen  100- 
foot  chords  and  a  chord  of  45.80  feet  at  the  end. 

The  dimensions  of  the  small  loop  are  of  no  importance,  as  it  is 
used  only  for  starting  and  slowing  up;  and  no  information  is 
available  as  to  the  size  in  this  particular  case.  In  some  tracks,  the 
small  loop  is  formed  by  prolonging  the  two  tangents  beyond  their 
intersection  and  connecting  them  by  a  circular  arc,  thus  making 
a  track  somewhat  like  a  figure  8  with  one  loop  very  much  smaller 
than  the  other.  The  form  shown  in  Fig.  75  requires  a  rectangle 
of  ground  2,900X1,060  feet  or  about  70.5  acres. 


\ 
\ 
\ 
\ 

\ 

/ 

Xf  A 

\ 

/ 

^. 

^fe  s\ 

k 

/ 

§ 

^§N$»-  1 

-£— 

47736  ft                     ^Nl! 

o 

A 

Fig.  76.— Surveyor's  Method  of  Laying  Out  Kite  Track. 

428.  The  proportions  of  the  kite  track  are  susceptible  of  consid- 
erable variation.  In  Fig.  77,  let  A  be  the  apex,  B  the  starting 
point,  and  Z  the  finish.  Then  BDEF  Z  =  5,280  ft. ;  or  B  D  E  = 
2,640  ft.  Call  the  distance  from  the  apex  to  the  starting  point  x, 
i.  e.,  A  B  =  A  Z=x  ft.    Then 

(T-x)  +  R  a  arc  1°  =  2,640, (1) 


ART.  2.]  HORSE-RACETRACKS.  285 

which  easily  becomes 

#(tan  a  +  0.01745  a°)  -  2,640  +  x,      ...     (2) 

in  which  tan  .a  stands  for  the  numerical  value  only.    Equation  (2) 
shows  that  x  and  either  R  or  a  may  be   assumed  arbitrarily. 


Fig.  77.— General  Form  of  Kite  Track. 

Equation  (2)  may  be  used  also  to  deduce  to  dimensions  of;  the 
small  loop,  in  which  case  either  R  or  the  length  of  the  curve  must 
be  assumed,  a  being  the  same  as  for  the  large  loop,  and  x  =  0. 

The  kite  track  is  two  or  three  seconds  faster  than  an  oval 
of  the  same  length;  but  it  is  not  satisfactory  to  the  spectators,  and 
consequently  is  not  much  used. 

429.  Oval  Track  with  Easement  Curves.  All  of  the  three  pre- 
ceding forms  are  defective  in  that  the  track  changes  instantly 
from  a  straight  line  to  a  circle  of  comparatively  short  radius.  It 
is  impossible  for  a  horse  at  any  considerable  speed  to  change  in- 
stantly from  a  right  line  to  a  curve;  and  if  the  change  is  made  in 
a  comparatively  short  space,  a  severe  shock  is  experienced  and  a 
considerable  effort  is  required.  The  ideal  race  track  should  change 
gradually  from  the  straight  to  the  curved  portion.  It  will  be 
shown  presently  that  on  the  curves  the  outer  portion  of  the  track 
should  be  higher  than  the  inner  edge,  to  facilitate  the  passage  of 
the  horse  around  the  curves.  This  super-elevation  is  not  re- 
quired on  the  straight  stretches.  With  the  forms  described  above, 
it  is  impossible  to  secure  at  all  points  the  proper  amount  of  super- 
elevation. The  total  super-elevation  can  not  be  attained  in- 
stantly; and  if  it  begins  on  the  straight  portion  and  reaches  the 
proper  amount  at  the  tangent  point,  it  is  an  obstruction  on  the 
straight  stretch;  and  if  it  begins  on  the  curve  and  gradually  in- 
creases to  the  proper  amount,  the  first  part  of  the  curve  does  not 
have  the  needed  super-elevation.  Therefore  the  straight  stretch 
of  the  track  should  be  joined  to  the  circular  portion  by  a  curve  of 
uniformly  varying  curvature.      This  easing  of  the  curves  is  not 


286  EQUESTRIAN  ROADS  AND  HORSE-RACE  TRACKS.    [CHAP.   VII. 

common  in  race-track  construction;  but  it  is  absolutely  necessary 
on  railroads,  is  very  important  in  bicycle  racing  (see  Chapter 
XX),  and  would  be  very  beneficial  on  horse-race  tracks. 

Various  curves  for  connecting  the  straight  and  the  circular 
portions  have  been  proposed,  but  the  best  is  the  transition  spiral.* 
In  this  curve,  the  radius  varies  inversely  as  the  distance  along  the 
curve. 

430.  Mile  Track.     Fig.  78  shows  one  quadrant  of  the  inside 

I07B4JL 


"t- 


Lengths  on  Pole  Une 
A  B  -  lanqent**        460.8  ft 
E>C-Sp/n7/  =         423.1 . 
CD-  Circular  Arc  «  4-36/  ' 
7bto/for  /  Quadrant  =/3200ft 


s  Inside  of  track 
jA/ *60.3jt y5/? 


~-Po/c  //rx  T  B 

Fig.  78.— One  Quadrant  of  Mile  Track  with  Transition  Spiral. 

curve  of  a  mile  oval  with  a  transition  spiral  between  the  straight 
and  the  circular  portions.  Except  for  the  easement  curve,  the 
track  is  substantially  the  same  as  the  standard  mile  oval  shown 
in  Fig.  70,  page  279. 

Either  of  two  methods  may  be  employed  in  laying  of  the 
spiral — that  by  deflection  angles  and  chords,  or  by  rectangular 
co-ordinates.  Table  29,  page  287,  contains  the  necessary  data 
for  the  first  method,  and  Table  30  those  for  the  second.  The  point 
P.S.  (point  of  spiral)  in  the  tables  is  the  point  B  in  Fig.  78,  and 
the  point  P.C.C.  (point  of  compound  curve)  is  C  in  Fig.  78. 

The  circular  portion  CD  is  most  readily  laid  out  by  successive 
chords.  The  deflection  angle  for  a  100-foot  chord  is  7°  0'  59"  or  prac- 
tically 7°1'.  Thearcfora  100-foot  chord  is  100.249  feet,and  hence  the 
number  100-foot  chords  is  4.3186  (  =  432.92 --100.245);  that  is  to 
say,  in  the  distance  CD  there  will  be  four  100-foot  chords  and  a 
chord  of  31.86  feet  at  the  end,  or  in  the  entire  circular  arc  at  one 

♦The  Railroad  Transition  Spiral,  by  Arthur  N.  Talbot,  6"  x  4",  p.  110,  3d  edi- 
tion, 1901,  Engineering  News  Publishing  Co.,  New  York. 


ART.   2. 


HORSE-RACE   TRACKS. 


287 


end  of  the  track  there  will  be   practically  eight  100-foot  chords 
and  one  chord  of  64.04  feet. 

TABLE  29. 

Chords  and  Deflection  Angles  for  Locating  the  Spiral  for 

the  Inside  Edge  of  the  Mile  Track. 


Point  on  Spiral. 

Distance  from  P.S. 
along  Curve. 

Deflection  Angle  at 

P.S.  from  Initial 

Tangent. 

P.S. 

00  ft. 

0°     00' 

1 

100   " 

0      33 

2 

150  " 

1      15 

3 

200  " 

2      13 

4 

225  " 

2      48 

5 

250  " 

3      28 

6 

275  " 

4       12 

7 

300  " 

5      00 

8 

325  " 

5      52 

9. 

350  " 

6      48 

10 

375  - 

7      48 

11 

400  " 

8      52 

P.C.C. 

420.1  ft. 

9      47 

TABLE  30. 

Rectangular  Co-ordinates  for  Locating  the  Spiral  for  the 

Inside  Edge  of  the  Mile  Track. 


Point  on  Spiral. 

Distance  from  the 

P.S.  on  the  Tangent 

Prolonged. 

Offset  Perpendicular 
to  the  Tangent. 

P.S. 

00       ft. 

0.0    ft. 

1 

100.0   " 

0.97  " 

2 

149.9  " 

3.27  " 

3 

199.7  " 

7.75  " 

4 

224.5  " 

11.04  " 

5 

249.2  " 

15.11  " 

6 

273.8  " 

20.11  " 

7 

298.0  " 

26.05  " 

8 

322.0  " 

33.08  " 

9 

345.6  " 

41.19  " 

10 

368.8  " 

50.54  " 

11 

391.4  " 

61.10  " 

P.C.C. 

409.2  " 

70.53  " 

431.  Half-mile  Track.  Fig.  79,  page  288,  shows  one  quadrant 
of  the  curve  of  the  inside  of  the  track  of  a  half-mile  track  having 
a  transition  spiral,  which  except  for  the  easement  curve  is  sub- 
stantially the  same  as  the  half-mile  track  shown  in  Fig.  73,  page 

282. 


288 


EQUESTRIAN  ROADS  AND  HORSE-RACE  TRACKS.     [CHAP.   VII. 


.  Tables  31  and  32,  contain  the  data  for  the  two  methods  of 
laying  out  the  transition  spiral.  The  deflection  angle  for  50-foot 
chords  is    7°    V  00".      The   arc    for    a    50-foot   chord   is   50.124 

_j SJSSff- 


Lznqfhs  on  Pole  Line 
A&=*Ta/?qer?t=         2245  ft 
BC=  Spira/=  2/8  6. 

CD=  Cinou/orr Arc=  2/6. 9  - 
Tora/for/Q(M7arrant=>  6600/9. 


I 

•a 


r/nsic/<z  of  f/z7Ck 
/         224Sft 


=4 


\i3fL 


2I5M- 


/ine 


Fig.  79, 


-Pole  //r?e  t       jj-j  " " 

One  Quadrant  of  Half-mile  Track  with  Transition  Spiral. 


feet;  and  hence  the  number  of  50-foot  chords  in  half  the  circular 
arc  is  4.2567,  or  in  the  entire  circular  curve  there  are  4.2567,  or  four 
50-foot  chords  and  one  chord  of  12.83  feet. 


TABLE  31. 
Chords  and  Deflection  Angles  for  Locating  the  Spiral  for  the 
•   Inside  Edge  of  the  Half-mile  Track. 


Point,  on  Spiral. 

Distance  from  P.S. 
along  Curve. 

Deflection  Angle  at 

P.S.  from  Initial 

Tangent. 

P.S. 

1 

2 
3 
4 
5 
6 
7 
8 
P.C.C. 

00  ft, 

25  " 

50  " 

75  " 
100  " 
125  " 
150  " 
175  " 
200  " 
215.4  ft. 

0°     00' 
0      08 

0  32 

1  13 

2  10 

3  23 

4  52 
6      40 
8      40 

10      00 

432.  SUPER-ELEVATION.  On  the  curves  the  outside  of  the 
track  should  be  higher  than  the  inside,  to  neutralize  the  effect 
of  centrifugal  force.  According  to  the  principles  of  mechanics, 
the  forre  required  to  deflect  a  body  from  a  rectilinear  path  is 


wv 


5r-s  in  which  w  is  the  weight  of  the  body,  v  the  velocity  in  feet 


ART.  2.] 


HORSE-HACE   TRACKS* 


289 


per  second,  R  the  radius  of  curvature  in  feet,  and  g  the  accelera- 
tion due  to  gravity  in  feet  per  second.  This  force  acts  radially 
in  the  plane  of  the  curve;  and  since  the  path  of  a  body  moving 
around  the  track  is  a  curve  whose  plane  is  horizontal,  the  cen- 
trifugal force  acts  horizontally. 

The  horse  is  acted  upon  by  two  forces — gravity  and  centrifugal 
force.  These  forces  and  their  resultant  are  shown  in  Fig.  80.  Tf 
the  track  is  level,  the  effect  of  the  centrifugal  force  is  the  same  as 
though  the  horse  were  traveling  upon  a  surface  inclined  at  an 
angle  a  with  the  horizontal;  but  if  the  outer  edge  of  the  track 
is  elevated  until  the  surface  is  perpendicular  to  the  resultant 
represented  by  Q  in  Fig.  80,  page  290,  the  effect  upon  the  horse 
is  the  same  as  though  he  were  traveling  upon  a  perfectly  level 
track. 

TABLE  32. 

Rectangular  Co-ordinates  for  Locating  the  Spiral  for  the 
Inside  Edge  of  the  Half-mile  Track. 


■ 

Point  on  Spiral. 

Distance  from  the 

P.S.  on  the  Tangent 

Prolonged . 

Offset  Perpendicular 
to  the  Tangent. 

P.S. 

oo    a. 

0.0    ft. 

1 

25.0  " 

0.06  " 

2 

50.0  '•« 

0.47  " 

3 

75.0  " 

1.60  " 

4 

99.9    ' 

3.78  " 

5 

124.6  " 

7.39  " 

6 

i49.o  :• 

12.70  " 

7 

172.9    •' 

20.11  '' 

8 

195.9  " 

29.83  " 

P.CC 

209.4  " 

37.06  " 



From  Fig.  80.  it  is  readily  seen  that  s  • 

tana=/S a) 

Expressing  v  in  terms  of  t,  the  number  of  minutes  required  to  go  a 
mile,  and  substituting  for  g  its  numerical  value  (32.16).  equation 
(1)  becomes 

241 
tana  =  -^ (2) 


290 


EQUESTRIAN  ROADS  AXD  HORSE-RACE  TRACKS.     [CHAP.  VII. 


This  formula  shows  the  relation  that  should  exist  between  the 
inclination  of  the  track,  and  the  number  of  minutes  required  to  go 
1  mile. 


Fio.  80. 

433.  For  the  mile  track  shown  in  Fig.  78,  page  286,  and  a  2- 
minute  speed,  a  should  be  0.15;  that  is,  the  inclination  of  the  sur- 
face of  the  track  on  the  circular  curve  should  be  15  vertical  in  100 
horizontal.  For  the  same  track  and  a  speed  of  a  mile  in  2  minutes 
and  40  seconds,  the  inclination  should  be  8  in  100,  and  for  a  mile 
in  3  minutes,  6.7  in  100.  For  the  half-mile  track  shown  in  Fig. 
79.  page  288,  the  inclination  on  the  circular  curve  should  be  prac- 
tically twice  that  for  the  mile  track  above. 

The  super-elevation  should  gradually  increase  from  nothing 
at  the  beginning  of  the  transition  spiral,  i.  e.,  at  the  end  of  the 
straight  stretch,  to  the  maximum  at  the  beginning  of  the  circular 
portion.  The  advantage  of  the  transition  spiral  (§  429)  is  that  its 
radius  of  curvature  decreases  as  the  distance  from  the  tangent 
point  increases,  and  therefore  the  super-elevation  at  every  point 
can  be  adjusted  so  as  always  to  exactly  neutralize  the  centrifugal 
force.  When  this  condition  is  secured,  the  effect  upon  the  horse 
will  be  the  same  as  though  he  were  traveling  upon  a  level  track  all 
the  time. 

There  is  a  little  room  for  choice  as  to  the  speed  for  which  the 
super-elevation  shall  be  adjusted      If  it  is  desired  to  build  a  track 


ART.   2.]  HORSE-RACE   TRACKS.  291 

upon  which  the  fastest  horses  can  make  the  fastest  time,  then  the 
super-elevation  should  be  computed  for  their  fastest  speed ;  but 
if  it  is  desired  to  build  a  track  upon  which  slower  horses  can  make 
their  fastest  time,  then  the  super-elevation  should  correspond 
to  the  fastest  speed  of  the  slower  horses. 

It  seems  to  be  the  practice  to  give  a  slope  of  1  in  13  (7.7  per 
100)  on  the  mile  track  shown  in  Fig.  70,  page  279,  and  on  the  half- 
mile  track  shown  in  Fig.  73,  page  282,  1  in  12  (8.5  per  100). 

Horsemen  claim  that  there  is  less  need  of  super-elevation  since 
the  introduction  of  the  low-wheeled  sulky;  but  the  claim  is  with- 
out foundation,  as  the  proper  inclination  is  independent  of  the 
height  of  the  wheel  of  the  racing  sulky. 

434.  GRADES.  It  is  desirable  that  the  track  should  be  level 
longitudinally;  but  this  is  not  absolutely  necessary.  A  number 
of  celebrated  tracks  are  not  level.  The  Cleveland,  Ohio,  track, 
a  very  noted  one,  has  an  ascent  of  16  inches  in  the  first  quarter 
and  24  in  the  second,  and  a  descent  of  30  inches  in  the  third  quarter 
and  10  inches  in  the  fourth.  Not  a  few  horsemen  believe  that  a 
slight  grade  is  an  advantage  (see  last  paragraph  of  §  70).  Fre- 
quently the  introduction  of  a  slight  grade  will  materially  decrease 
the  cost  of  construction. 

435.  THE  SURFACE.  The  surface  should  be  formed  of  a  soil 
that  packs  well  and  does  not  "cup,"  i.e.,  curl  up  when  sprinkled. 
Clay,  loam,  gumbo,  sandy  loam,  and  muck  are  all  good.  If  the 
natural  soil  is  clear  sand,  it  should  be  covered  with  a  top  dressing 
of  clay  or  loam  3  to  4  inches  deep,  which  is  then  thoroughly  har- 
rowed in. 

436.  Water  is  the  first  requisite  to  keep  a  track  in  good  condi- 
tion. If  the  track  becomes  too  dry,  it  loses  its  elastic  or  "  springy  " 
condition,  and  becomes  dusty;  and  therefore  to  keep  it  in  proper 
condition,  it  should  be  sprinkled  when  dry.  The  sprinkler  should 
deliver  the  water  liberally  and  evenly  in  a  fine  spray. 

The  second  requisite  for  proper  maintenance  is  a  good  harrow. 
The  proper  time  to  harrow  the  track  is  after  a  rain  or  after  sprink- 
ling If  the  track  is  dry,  harrowing  unduly  pulverizes  the  soil, 
causing  it  to  lose  its  cohesive  properties  and  become  "rotten" 
or  "dead,"  and  "cuppy."  Too  frequent  or  too  deep  harrowing 
produces  substantially  the  same  result.     The  harrow  should  have 


292  EQUESTRIAN  ROADS  AND  HORSE-RACE  TRACKS.    [CHAP.  VII. 

many  small  sharp  short  teeth,  so  distributed  that  no  two  follow 
in  the  same  line. 

The  implement  of  the  next  importance  in  the  care  of  a  race 
track  is  a  leveler  or  "float."  This  consists  of,  say,  five  scantlings 
2  inches  by  4  inches  by  16  feet  set  parallel  to  each  other  about  4 
feet  apart.  On  top  of  these  are  firmly  spiked  three  planks  2 
inches  by  6  inches  by  16  feet.  The  team  is  attached  a  little  to  one 
side  of  the  center;  and  then  as  the  frame  is  drawn  over  the  track 
the  clods  are  crushed,  any  slight  depressions  or  gullies  are  filled, 
and  any  surplus  loose  earth  and  pebbles  are  worked  to  the  outside 
of  the  track.  It  is  important  that  the  implement  be  large  enough 
to  cover  considerable  area,  as  otherwise  it  will  follow  the  depressions 
of  the  surface,  making  them  larger  and  deeper  rather  than  filling 
them  up;  and  it  is  also  important  that  the  outer  end  of  the  scraping 
edges  may  be  unobstructed,  so  that  any  pebbles  may  be  worked 
toward  the  outside  of  the  track. 

In  the  spring  or  after  a  severe  storm  which  has  washed  consid- 
erable loose  earth  down  to  the  inside  of  the  curves,  it  may  be 
necessary  to  go  over  the  track  with  a  scraping  grader  (§  142)  to  work 
the  surplus  material  back  to  the  outside  and  fill  up  the  gullies. 
The  frequent  use  of  the  scraping  grader  is  rendered  unnecessary 
by  the  continuous  use  of  the  leveler  described  above. 

437.  DRAINAGE.  To  secure  good  surface  drainage,  it  is  cus- 
tomary to  give  the  surface  on  the  straight  stretches  an  inclination 
inward  of  1  or  2  feet  to  100  feet.  This  inclination  is  not  enough 
to  materially  interfere  with  the  traveling  of  the  horses,  and  is  of 
great  advantage  in  keeping  the  track  in  good  condition. 

About  2  feet  inside  of  the  pole  fence,  there  should  be  a  ditch 
1  foot  deep  and  2  feet  wide;  and  from  the  inside  edge  of  the  track 
to  the  ditch  there  should  be  a  slight  inclination  and  an  opportunity 
for  an  unimpeded  flow  of  the  water.  From  the  bottom  of  the  ditch 
should  be  frequent  inlets  to  a  tile  which  will  carry  all  surface  water 
speedily  and  entirely  away. 


PART    II. 

STBEET    PAVEMENTS. 


439.  Good  pavements  are  necessary  to  the  highest  develop- 
ment of  the  commercial,  sanitary  and  esthetic  life  of  the  city.  The 
large  proportion  of  people  now  dwelling  in  cities  makes  the  subject 
of  pavements  an  important  one  at  present;  and  the  fact  that  the 
urban  population  is  increasing  much  more  rapidly  than  the  rural, 
and  also  the  fact  that  the  public  is  awakening  to  the  necessity  of 
ameliorating  the  condition  of  life  in  the  city,  will  make  pavements 
of  increasing  concern  in  the  future. 

440.  The  importance  of  pavements  as  an  element  in  municipal 
finance  seems  not  to  be  fully  appreciated,  and  this  subject  has  not 
received  from  municipal  engineers  and  city  officials  the  attention 
and  study  its  importance  merits.  Whether  measured  by  their 
influence  upon  the  commercial,  sanitary  or  esthetic  life  of  the  city, 
or  by  the  amount  of  money  invested  in  them,  street  pavements 
belong  in  the  first  rank  of  importance  in  municipal  affairs. 

Until  quite  recently  no  attempt  has  been  made  to  collect  statis- 
tics concerning  American  pavements.  Bulletin  No.  24  (September 
1900)  of  the  U.  S.  Department  of  Labor  contains  statistics  as  to 
the  number  of  square  yards  of  pavements  in  each  of  the  one  hun- 
dred and  twenty-nine  cities  having  a  population  of  30,000  or  over, 
but  gives  no  data  concerning  the  cost  of  these  pavements.  An 
approximate  estimate  of  their  cost  may  be  arrived  at  by  assuming 
an  average  price  for  such  work.  The  total  number  of  square  yards 
of  each  of  the  principal  kinds  of  pavements  and  their  approximate 
cost  is  as  follows: 

Asphalt,— sheet  and  block 36  585  322  sq.  yd.  at  $2 .  75  =  $100  609  635 

Brick  .  : 21  648  768   "  "  "  1 .  75  =  37  885  344 

Cobblestone 21600  245"  "  "  0.80=  17  280  196 

Granite  block 30  816  521    "  "  "  3.50  =  107  857  823 

Gravel 38  645  022"  "  "  0.20=  7  729  004 

Macadam 82  680  545    "  "  "  0. 75  =  62  010  409 

Wood  block 27  727  572   "  "  "  1 .25  =  34  659  465 

Other  kinds                                  )  9  553  000   "  "  "  2.50=  23  882  500 

'(  8  888  200  "  "  "  1.00=  8  888  200 

Total 278  145  195  "  "  $400  812  576 

293 


294  STBEET   PAVEMEXTS. 

Under  "other  kinds"  in  the  above  table  is  included  sandstone  and 
limestone  block,  rubble,  shell,  tar  distillate,  granolithic,  and  per- 
haps telford — at  least  a  number  of  cities  separate  macadam  and 
telford  pavements  in  their  official  reports.  A  number  of  cities  have 
large  areas  of  sandstone  block,  and  from  private  investigations 
the  author  concludes  that  of  the  "other  kinds"  at  least  9,553,000 
square  yards  are  sandstone  block,  and  this  has  been  entered  sepa- 
rately in  the  above  summary. 

From  the  preceding  table  it  appears  that  the  pavements  in 
these  cities  have  cost  $400,812,576;  and  as  the  total  population 
is  19,036,845,  the  pavements  have  cost  #21.06  per  capita  of  their 
present  population.  The  area  of  pavements  per  capita  varies 
greatly  in  the  different  cities,  being  practically  independent  of  the 
size  and  location  of  the  city;  and  this  average  seems  to  agree 
fairly  well  with  the  area  of  pavements  in  a  number  of  very  much 
smaller  cities  investigated  by  the  author.  Therefore  it  will  be 
assumed  that  the  above  average  is  representative  of  the  entire 
country.  According  to  the  U.  S.  Census  for  1900  there  are 
24,992,199  people  dwelling  in  cities  of  8,000  population  or  over. 
Therefore  the  investment  in  pavement  in  these  cities  amounts  to 
$514,836,179.  Measured  by  the  money  invested,  street  pave- 
ments are  probably  the  most  important  of  any  single  class  of  engi- 
neering construction  except  steam  railroads. 

441.  According  to  Bulletin  No.  100  of  the  1890  census,  the 
average  annual  expenditure  for  pavement  construction  and  repairs 
in  the  cities  of  the  United  States  having  a  population  of  10,000  or 
over,  was  $1.72  per  capita,  being  $1.54  in  the  cities  having  more 
than  100,000  population  and  $2.04  in  cities  from  10,000  to  100,000. 
If  the  same  rate  of  expense  obtained  in  1900,  the  total  annual  ex- 
penditure for  pavements  in  cities  of  8,000  or  more  population 
was  $43;000,000. 

The  first  cost  of  pavement  and  also  their  annual  cost  is  of  such 
magnitude  that  merely  as  a  financial  question  street  pavements 
deserve  the  most  careful  attention  and  systematic  study. 


CHAPTER  VIII. 

PAVEMENT  ECONOMICS. 

442.  BENEFITS  OF  PAVEMENTS.  The  effect  of  pavements  upon 
city  life  is  so  important  and  so  far  reaching  that  no  enumeration 
is  likely  to  include  all  of  the  benefits;  but  nevertheless  it  will  be 
of  advantage,  particularly  in  discussing  the  proper  distribution 
of  their  cost,  to  enumerate  some  of  the  more  important  of  the 
benefits  resulting  from  the  construction  of  pavements.  Briefly 
the  principal  advantages  are : 

1.  Good  pavements  lessen  the  tractive  power,  and  decrease  the 
cost  of  transportation.  See  §  4-8  for  a  discussion  of  the  cost  of 
transportation. 

2.  They  increase  fire  protection  by  facilitating  the  transporta- 
tion of  the  fire  engine. 

3.  They  establish  a  permanent  grade,  which  is  an  important 
matter  when  other  improvements  are  to  be  made. 

4.  Pavements  add  to  the  appearance  of  the  street  by  giving 
a  uniform  surface  instead  of  the  irregular  one  of  an  unpaved  street. 

5.  They  increase  cleanliness,  since  the  pavement  is  less  dusty 
in  a  dry  time  and  less  muddy  in  a  wet  time  than  an  unpaved  street. 

6.  They  increase  healthfulness  by  removing  holes  filled  with 
mud  and  filth. 

7.  Pavements  permit  pleasure  driving  at  all  seasons,  and  facili- 
tate social  intercourse. 

8.  Pavements  allow  the  use  of  bicycles,  which  furnish  cheap 
transportation  and  healthful  recreation  to  many. 

In  discussions  of  this  subject  it  is  customary  to  include  the 
enhanced  value  of  the  property  as  one  of  the  advantages  of  a  pave- 
ment; but  the  increase  in  the  value  of  the  property  is  simply  a 

293 


296  PAVEMENT   ECONOMICS.  [CHAP.  Till, 


measure  of  the  benefits  enumerated  above,  and  hence  should  not 
be  again  included.* 

The  first  three  benefits  above  may  be  regarded  as  financial 
advantages  and  the  last  four  as  sanitary  and  esthetic.  It  is  im- 
possible to  compute  even  approximately  the  financial,  much  less 
the  sanitary  and  esthetic  value  of  good  pavements;  but  it  is  safe 
to  say  that  they  are  an  absolute  necessity  to  both  the  business 
and  resident  districts  of  the  larger  cities  and  also  for  business 
districts  of  the  smaller  cities,  and  that  on  residence  streets  of  small 
cities  good  pavements  add  greatly  to  the  health,  comfort  and 
pleasure  of  life. 

443.  Apportionment  of  the  Cost.  There  is  much  discus- 
sion as  to  who  in  equity  should  bear  the  cost  of  the  pavement. 
There  are  three  distinct  views.  1.  A  few  claim  that  as  they  own 
neither  a  horse  nor  a  vehicle  and  do  not  use  the  pavement,  they 
should  not  be  required  to  pay  for  it.  Although  a  resident  may 
not  trayel  upon  the  pavement,  it  is  used  by  those  who  serve  him; 
and  a  pavement  confers  other  benefits  besides  those  relating  to 
transportation.  It  is  entirely  impracticable  to  distribute  the  ex- 
pense according  to  the  use  made  of  the  pavement.  2.  Others 
claim  that  the  pavement  is  for  the  benefit  of  the  general  public 
of  the  city  at  large,  and  hence  the  abutting  property  should  pay  no 
more  than  that  in  other  parts  of  the  city.  This  claim  ignores  the 
fact  that  the  abutting  property  secures  a  distinct  benefit  for  which 
it  should  be  required  to  pay.  Laying  at  least  part  of  the  cost  upon 
the  property  tends  to  discourage  a  demand  for  lavish  expendi- 
tures for  unnecessary  improvements,  that  possibly  might  be  in- 
sisted upon  if  the  city  contributed  the  entire  cost.  3.  Many  hold 
that  the  benefits  accrue  only  to  the  abutting  property,  and  that 
therefore  the  owner  of  the  abutting  property  should  bear  the  entire 
cost.  This  claim  disregards  the  fact  that  the  pavement  is  for  the 
use  of  the  general  public,  and  benefits  all  the  people  and  all  those 
having  business  interests  in  the  city.  An  improvement  in  any 
part  of  the  city  is  an  indirect  benefit  to  the  city  as  a  whole.  In 
excuse  of  this  method  of  payment,  it  is  sometimes  claimed  that, 


*  For  an  interesting  study  of  the  effect  of  pavements  in  increasing  the  value  of 
abutting  property,  see  Engineering  Record,  Vol.  25,  p.  418-19. 


APPORTIONMENT   OF  THE   COST.  297 

although  the  pavement  confers  a  general  benefit,  the  inequality 
will  be  compensated  when  all  the  streets  are  paved.  The  answer 
is  that  all  the  streets  may  never  be  paved,  and  besides  traffic  natu- 
rally concentrates  on  certain  lines  and  nearly  ignores  certain  others, 
and  therefore  some  pavements  will  require  much  more  care  and  ex- 
pense than  others.  Further,  there  should  be  no  objection  to  letting 
every  property  holder  pay  a  part  of  his  ultimate  share  as  the  work 
progresses,  instead  of  paying  it  in  a  lump  sum  when  the  street  in 
front  of  his  own  property  is  paved.  The  second  or  third  view  or  a 
combination  of  them  usually  obtains.  Table  33,  page  298,  shows 
the  method  of  apportioning  the  expense  in  fifty  American  cities.* 

The  practice  is  slightly  different  for  the  grading,  the  original 
paving,  and  the  re-paving.  The  cost  of  grading  in  54  per  cent  of 
these  cities  is  all  paid  by  the  abutting  property,  in  32  per  cent  all 
by  the  city,  and  in  14  per  cent  part  by  each  in  varying  proportions. 
The  cost  of  the  original  paving  in  62  per  cent  of  the  cities  is  charged 
entirely  to  the  private  owner,  in  22  per  cent  entirely  to  the  city,  and 
in  16  per  cent  it  is  divided  between  the  two.  The  cost  of  re-paving 
in  42  per  cent  of  the  cities  is  paid  wholly  by  the  property,  in  40 
per  cent  wholly  from  the  general  tax,  and  in  18  per  cent  it  is  di- 
vided between  the  two.  In  some  cities  a  street  in  an  addition  or 
subdivision  is  not  accepted  by  the  municipal  authorities  until  it 
has  been  graded,  and  hence  it  is  done  at  the  expense  of  the  abut- 
ting property;  but  on  the  other  hand,  some  cities  are  willing  to 
bear  a  part  of  the  cost  of  the  street  improvement,  and  therefore 
pay  for  the  grading.  Only  one  quarter  of  the  above  cities  pay  the 
major  part  of  the  cost  of  the  original  paving,  while  40  per  cent  pay 
the  major  part  of  the  cost  of  re-paving.  It  is  the  custom,  where 
there  is  a  car  track  on  the  street,  to  require  the  railroad  to  pave 
an  8-foot  strip  for  each  track,  the  remainder  being  divided  be- 
tween the  abutting  property  and  the  city  at  large  in  the  same  pro- 
portion as  on  the  streets  where  there  is  no  track.  In  some  cities 
intersecting  streets  are  regarded  as  municipal  property,  and  the 
cost  of  paving  the  intersection  is  assessed  against  the  street,  i.  e., 
against  the  city;  but  in  others  the  cost  of  paving  the  street  inter- 


*From    an  article  on  Theory  and  Practice   of  Special  Assessments  by  J.  L. 
YanOrnum,  in  Traus.  Amer.  Soc.  of  Civil  Engineers,  Vol.  38,  p.  336-422. 


298 


PAVEMENT    ECONOMICS. 


[CHAP.   VIII. 


TABLE  33. 
Apportionment  op  Cost  of  Pavements  in  Fifty  Cities. 


a.  1  sq.  yd.  for  each  front  foot ;  city  remainder 

b.  3i  sq.  ft.  "       "  "       "     ;     " 

c.  City  pays  for  street  intersections. 

d.  City  does  not  pay  for  street  intersections. 


d 

Locality. 

Grading. 
Per  Cent 
Paid  by 

Original 
Paving. 
Per  Cent 
Paid  by 

Re-paving. 
Per  Cent 
Paid  by 

State. 

City. 

Prop- 
erty. 

City. 

Prop- 
erty. 

City. 

Prop- 
erty. 

City. 

l 

Montgomery 

Little  Rock 

San  Francisco 

Hartford 

50 
100 
100 

50 

'  100 
100 
100 
100 

50 
100 

50 

"d" 

100 

100 

"  '  25  ' 
100 

50 
100 
100 

67 

a 

' '  50  ' 

67 

50 

100 

100 

100 

100 

100 

75 

'  Yob" ' 

50 

50 
100 

50 

ioo* 

2 
3 

Arkansas 

California 

Connecticut 

Dist.  of  Columbia.. 

Delaware 

Florida 

4 

33 

'  100  ' 

100 
50 
33 
50 

"d" 
c 

' '  50  ' 

67 

50 

100 

100 

'  Yob' ' 

100 

iob' 

100 
50 
33 

50 

5 
6 

7 
8 
9 

New  Haven 

Washington 

Wilmington 

Jacksonville 

' "  50  ' 

10 

Augusta 

50 

100 
100 

11 

Peoria 

1? 

Indianapolis 

Burlington 

d 

13 

100 

14 

Topeka  

Louisville 

New  Orleans 

'  100  ' 
75 

15 

Kentucky 

Louisiana 

100 

16 
17 

25 
100 

75 

25 

100 

18 

Maryland 

Massachusetts. . . . 

Michigan 

Minnesota 

Missouri 

Nebraska 

New  Hampshire.  . 
New  Jersey 

New  York 

Ohio 

Baltimore 

Lowell 

100 
100 

100 

19 

100 
100 
100 

c 

c 

c 
100 

'  'lOO  ' 
100 
100 
100 
100 
100 

'  Yob ' 

100 

?0 

Springfield 

100 

100 

?1 

Worcester 

100 
100 

100 

99, 

Detroit 

c 

100 

'  100  ' 
50 
100 

"d" 

'  '  2c 
c 

'  100  " 

100 
100 
100 
100 
100 
100 

'  100 
100 
100 
100 
100 
100 
100 
100 
98 
100 
100 
100 
100 
100 

?3 

Minneapolis 

24 
25 
?6 

St.  Paul 

Kansas  City 

St.  Louis 

100 
100 



97 

Omaha 

50 

..... 

?8 

100 

?9 

100 
100 
100 
100 
100 
100 
100 
100 
98 
100 
100 
100 

'  'l  00  ' 
100 

30 

Paterson 

100 

31 

Albany 

d 

100 

50 

100 

d 

32 

Brooklyn 

50 

33 

Buffalo 

34 

New  York 

Rochester 

Syracuse  

ioo* 

35 
36 

'  '  2c 
c 

100 
100 
98 
100 
100 
100 

37 

Cincinnati 

Dayton 

2c 

38 

39 

Portland 

40 
41 

Pennsylvania  .... 

Rhode  Island 

South  Carolina.  .  . 
South  Dakota. . . . 

Tennessee 

Utah 

Harrisburg 

Philadelphia 

ioo* 

4? 

'  160  ' 

100 

c 
100 

c 
100 

c 

50 

'  Yob ' 
'  Yob ' 

100 

50 

43 

Providence  

100 

44 

100 

c 
100 

50c 
100 

c 

'  100  ' 

'  100  ' 

'  100  ' 
100 

100 

45 
46 

Sioux  Falls 

100 

c 

100 

47 

50 

48 

100 

49 

Washington 

Wisconsin 

Seattle  ... 

100 
100 

50 

Milwaukee 

100 

SPECIAL   ASSESSMENTS.  299 


sections  is  included  in  the  charge  against  the  abutting  property. 
In  most  cities  lots  owned  by  the  municipality  pay  the  same  propor- 
tion of  the  cost  of  the  street  improvements  as  private  property, 
although  usually  special  authority  is  required  thus  to  assess  mu- 
nicipal property. 

Table  33  also  shows  that  as  a  rule  the  eastern  and  southern 
cities  pay  a  larger  proportion  of  the  cost  of  pavements  than  do  the 
western.  This  difference  in  practice  is  probably  due  chiefly  to  the 
limited  revenues  of  new  cities  and  to  the  many  demands  upon 
the  general  tax  for  the  numerous  and  varied  necessities  of  rapidly 
growing  municipalities;  consequently  the  cost  of  pavements,  im- 
provements having  a  definite  local  benefit,  have  been  charged  to 
the  abutting  property.  It  is  equitable  and  just  that  the  cost  should 
be  borne  jointly  by  the  private  property  and  the  city  at  large, 
since  then  the  cost  falls  upon  both  interests  which  directly  profit 
by  the  improvement,  and  neither  receive  a  substantial  benefit 
without  sharing  in  its  cost. 

Ordinarily  the  proportion  of  the  expense  to  be  borne  by  the 
municipality  and  by  the  private  property  is  determined  wholly 
by  financial  considerations  or  usage,  and  is  made  uniform  over  the 
entire  city;  while  equity  and  justice  demand  that  a  distinction 
should  be  made  depending  upon  the  character  of  the  traffic.  The 
interests  of  the  general  public  in  a  street  vary  greatly  between 
a  residence  street,  a  business  street,  and  a  general  thoroughfare. 
To  pave  the  first  the  public  should  pay  only  a  small  share,  say,  20 
or  30  per  cent ;  for  the  second,  say,  40  or  50  per  cent ;  and  for  the 
third  60  or  75  per  cent.  Some  such  variation  in  the  proportion 
to  be  borne  by  the  two  interests  finds  further  justification  in  the 
fact  that  if  the  street  becomes  a  general  thoroughfare,  some  of 
the  benefits  enumerated  in  §  442  as  accruing  to  the  abutting  prop- 
erty may  be  nullified  by  the  noise  and  dirt. 

444.  Special  Assessments.*  The  proportion  of  the  cost  of 
a  pavement  paid  by  the  private  property  is  usually  collected  as 
a  special  assessment,  which  has  been  defined  as   "a   compulsory 


*  For  an  interesting  and  instructive  discussion  of  the  history  and  theory  of 
special  assessments,  see  Special  Assessments  by  Victor  Rosewater — Vol.  2,  No.  3 
of  Studies  in  History,  Economics  and  Public  Law.  152  p.,  6  x  9  inches,  Columbia 
College,  New  York,  1893.   See  also  the  article  referred  to  in  the  foot  note  on  page  297. 


300  PAVEMENT   ECONOMICS.  [CHAP.  VIII. 

contribution  paid  once  and  for  all  to  defray  the  cost  of  a  special 
improvement  to  property,  undertaken  in  the  public  interest,  and 
levied  by  the  government  in  proportion  to  the  special  benefits 
accruing  to  the  property  owner."  Special  assessments  differ 
from  taxes,  both  general  and  special,  in  that  the  former  are  based 
upon  a  direct  and  measurable  benefit  conferred  upon  the  con- 
tributor, which  is  the  measure  of  his  liability  to  be  taxed;  while 
taxes  are  levied  for  the  maintenance  of  the  institutions  and  inter- 
ests of  the  government,  without  reference  to  the  particular  benefits 
conferred,  according  to  the  ability  of  the  contributor  to  pay. 
The  construction  of  pavements  to  be  paid  for  by  special  assess- 
ment must  be  done  under  the  direction  of  the  public  officials. 

In  a  general  way  it  may  be  said  that  there  are  two  distinct 
methods  of  apportioning  the  amount  to  be  paid  by  the  private 
property;  viz.:  (1)  according  to  the  frontage,  and  (2)  according 
to  the  area. 

445.  Frontage  Rule.  By  far  the  more  common  method  of 
apportioning  the  assessments  is  pro  rata  according  to  the  front- 
age upon  the  ,  improvement.  This  method  is  often  designated 
as  the  front-foot  rule.  Of  the  forty-five  cities  in  Table  33,  page  298, 
which  assess  the  private  property  for  street  improvements,  thirty- 
eight  or  84  per  cent  follow  the  frontage  rule,  three  use  a  combina- 
tion of  frontage  and  area,  one  uses  area  alone,  one  value  alone,  and 
in  two  of  the  cities  the  method  employed  is  left  to  the  judgment 
of  the  assessing  board. 

Ordinarily  the  frontage  is  an  equitable  basis  upon  which  to 
distribute  the  cost;  but  under  some  circumstances  a  rigid  appor- 
tionment according  to  frontage  gives  anomalous  results.  For 
example,  if  most  of  the  lots  have  their  shorter  side  on  the  improve- 
ment and  one  has  its  longer  side  thus  placed,  the  frontage  rule  will 
give  inequality — particularly  if  the  latter  lot  is  very  narrow.  This 
condition  frequently  occurs — for  example  where  the  most  of  the 
lots  front  upon  the  street  to  be  paved,  while  some  front  upon  an 
intersecting  street.  In  this  case,  it  is  customary  to  extend  tht> 
assessment  to  the  middle  of  the  block;  that  is,  assess  the  lots 
between  the  pavement  and  the  center  of  the  block,  in  which  case; 
it  becomes  a  difficult  matter  to  determine  the  equitable  portiou 
for  each  of  these  lots.     A  rigid  adherence  to  the  frontage  rule 


SPECIAL   ASSESSMENTS.  301 

sometimes  works  injustice  near  the  intersection  of  two  streets 
cutting  each  other  at  an  acute  angle.  However,  no  method  can  be 
devised  that  may  not  require  modification  to  fit  unusual  conditions. 

446.  Area  Rule.  In  a  few  cities.  7  per  cent  of  those  in  Table 
33,  page  298,  the  cost  of  street  improvement  is  distributed  in  pro- 
portion to  the  area  of  the  abutting  lots;  but  usually  the  area  is 
used  in  combination  with  the  frontage.  Thus  in  Brooklyn,  N.  Y., 
60  per  cent  of  the  cost  is  distributed  in  proportion  to  the  frontage 
and  40  per  cent  according  to  the  area.  An  amendment  to  the 
charter  of  St.  Louis  proposes  to  charge  25  per  cent  of  the  cost  of 
the  pavement  according  to  the  frontage  and  75  per  cent  according 
to  the  area.  The  area  rule  finds  its  greatest  justification  on  curved 
streets. 

447.  Corner  lots  are  usually  the  cause  of  irritation  and  objection 
under  either  the  frontage  or  the  area  rule,  and  the  method  of  assess- 
ing them  differs  materially  in  different  cities.  Tn  some  cases  each 
margin  is  considered  a  front  on  its  proper  street,  without  any 
modification  in  the  rate  of  assessment;  in  a  few  cases  under  the 
area  rule  an  additional  per  cent  is  imposed  upon  the  corner  lot  for 
the  pavement  of  either  street;  but  usually  the  corner  is  assessed 
according  to  frontage  at  a  less  pro  rata  than  the  inside  lots,  since  it 
may  be  assessed  on  both  streets  * 

448.  Terms  of  Payment.  There  are  various  methods  of  pay- 
ing the  assessment.  1.  The  entire  amount  may  become  a  lien 
upon  the  property  as  soon  as  the  work  is  completed,  to  be  collected 
(a)  by  the  contractor,  or  (b)  by  the  city  acting  only  as  collecting 
agent  for  the  contractor,  or  (c)  by  the  city,  which  also  becomes 
responsible  to  the  contractor  for  the  payment  of  the  money.  2. 
The  amount  may  be  divided  into  equal  annual  installments,  usu- 
ally five  or  ten,  with  interest  on  deferred  payments,  to  be  collected 
(a)  by  the  contractor,  or  (b)  by  the  city,  the  contractor  receiving 
special  paying-district  bonds,  or  (c)  by  the  city,  the  contractor 
receiving  general  city-bonds.  3.  The  city  may  raise  a  paving 
fund  by  general  tax  or  by  selling  bonds,  and  pay  for  improve- 
ments as  made,  independent  of  the  collection  of  the  special  assess- 

*  For  a  summary  of  judicial  decisions  on  this  and  similar  matters,  see  Trans. 
Amer.  »oo.  of  Civil  Engineers,  Vol.  38,  p.  381,  §  20. 


302  PAVEMENT    ECONOMICS.  [CHAP.   VIII. 

ments.  The  second  method  is  the  more  common.  The  first  is 
objectionable  because  the  amount  becomes  immediately  due;  and 
the  third  is  objectionable  on  account  of  the  difficulty  of  making 
the  assessments  and  collections  keep  pace  with  each  other,  and  also 
because  of  a  tendency  to  produce  extravagance. 

449.  Legality  of  Levy.  Special  assessments  can  be  levied  only 
under  explicit  authority  of  the  law.  The  different  states  have 
very  complete  and  explicit  statutes  governing  special  assessments; 
and  the  courts  always  hold  that  any  material  departure  from  the 
prescribed  procedure  invalidates  the  assessment. 

450.  Guaranteeing  Pavements.  It  is  a  common  custom 
to  require  the  contractor  to  guarantee  the  pavement  for  a  term 
of  years,  which  guarantee  is  supported  either  by  an  indemnifying 
bond  or  by  a  portion  of  the  cost  of  the  pavement  retained  by  the 
municipality  until  the  expiration  of  the  specified  period.  In  some 
cases  the  guarantee  is  an  agreement  that  if  time  shall  reveal  that 
the  materials  or  the  method  of  construction  are  not  according  to 
the  contract,  the  contractor  shall  make  the  defect  good;  but  in 
other  cases,  the  so-called  guarantee  is  virtually  a  contract  to  main- 
tain the  pavement  for  the  specified  period  and  to  turn  it  over  in 
good  condition  at  the  end  of  that  time. 

Apparently  the  guarantee  originated  in  this  country  with  the 
introduction  of  sheet  asphalt  pavements.  The  material  was 
new,  the  method  of  laying  it  was  untried,  and  hence  no  city  would 
run  the  risk  of  paying  for  an  unknown  and  uncertain  pavement; 
consequently  the  contractor  agreed  to  guarantee  the  pavement 
for  a  period  of  years.  At  present  most  cities  continue  to  exact  a 
guarantee  for  asphalt  pavement,  ranging  from  five  to  fifteen  years, 
on  the  ground  that  the  method  of  testing  the  material  and  the 
manner  of  laying  it  are  too  little  understood  by  engineers  to  insure 
good  and  durable  work  without  a  guarantee.  At  the  beginning 
of  the  use  of  brick  as  a  paving  material  a  guarantee  was  sometimes 
demanded;  but  at  present  it  is  as  a  rule  not  required  with  this 
material. 

451.  The  requirement  of  a  guarantee  of  the  pavement  is  justi- 
fiable when  the  material  to  be  used  is  new  and  there  is  little  or  no 
opportunity  for  the  engineering  department  to  acquire  the  knowl- 
edge necessary  for  an  effective  inspection  of  the  work;  but  as  a 


GUARANTEEING  PAVEMENTS.  303 

rule  a  guarantee,  particularly  for  a  long  time,  is  unwise  for  the 
following  reasons:  1.  The  contractor  has  no  control  over  the 
street  after  the  pavement  is  completed;  and  it  is  difficult  to  dis- 
criminate between  defects  due  to  improper  material  and  the  effects 
of  ordinary  wear,  which  may  differ  materially  on  different  streets. 
It  is  also  difficult  to  discriminate  between  defective  workmanship 
and  damages  due  to  causes  for  which  the  contractor  is  in  nowise 
responsible,  as,  for  example,  fires,  escape  of  illuminatng  gas,  set- 
tlement of  trenches  made  after  the  completion  of  the  pavement, 
etc.  2.  It  is  difficult  to  enforce  the  guarantee  clause  if,  on  the 
one  hand,  the  engineering  department  inspects  the  material  and 
accepts  the  workmanship ;  and,  on  the  other  hand,  if  a  representa- 
tive of  the  city  does  not  inspect  the  work  there  is  liability  that  the 
streets  may  be  needlessly  obstructed  and  the  public  greatly 
inconvenienced  by  a  bungling  experiment  by  the  contractor.  The 
difficulty  of  enforcing  a  guarantee  is  much  less  in  a  large  city  where 
there  is  more  work  to  be  had  and  where  the  contractor  desires  to 
protect  his  reputation  with  a  view  to  securing  contracts  in  the 
future,  than  in  a  small  city  having  but  little  work;  and  the  diffi- 
culty is  still  further  increased  if  the  law  requires  that  the  con- 
tract shall  be  let  to  the  lowest  responsible  bidder — as  is  usually 
the  case. 

The  contractor  objects  to  the  guarantee,  not  without  justice, 
on  the  following  grounds:  1.  The  specifications  are  prepared  by 
the  engineering  department  of  the  city,  and  as  the  quality  of  the 
material  and  the  method  of  construction  is  prescribed  by  the  city 
and  subject  to  the  approval  of  its  representatives,  the  contractor 
should  not  be  held  responsible  for  the  result.  However,  the  suffi- 
cient answer  to  this  objection  is  that  the  contractor  accepts  the 
specifications  when  he  enters  into  contract,  and  is  therefore  right- 
fully bound  by  them.  2.  The  expense  is  needless  and  excessive, 
whether  an  indemnifying  bond  is  required  or  a  per  cent  of  the  con- 
tract price  is  retained,  which  expense  in  the  long  run  adds  to  the 
cost  of  the  pavement.  It  is  more  expensive  to  the  contractor  if 
the  city  retains  a  per  cent  of  the  contract  price,  since  a  portion  of 
his  capital  is  then  tied  up,  which  in  turn  drives  out  the  small  con- 
tractor, decreases  competition,  and  tends  to  increase  the  cost  of 
the  pavement.     On  the  other  hand,  the  interests  paying  for  the 


304  PAVEMENT    ECONOMICS.  [CHAP.   YIH. 

pavement  are  better  protected  if  the  city  retains  a  per  cent  than 
if  an  indemnifying  bond  is  accepted,  since  in  the  former  case  the 
city  has  the  money  in  hand  with  which  to  make  the  needed  repairs 
in  case  the  contractor  fails  to  do  so;  but  the  proper  care  of  such 
deferred  payments  adds  materially  to  the  labor  and  responsibility 
of  municipal  administration. 

The  contributing  property  holders  and  citizens  favor  the  guar- 
antee as  a  defense  against  incompetent  or  dishonest  city  officials 
and  employees.  The  guarantee  is  also  sometimes  defended  on  the 
ground  that  it  is  the  cheapest  method  of  securing  good  work, 
since  it  is  impossible  at  reasonable  cost  for  the  engineering  depart- 
ment to  inspect  all  stages  of  the  preparation  of  the  material  or  to 
acquire  the  knowledge  necessary  for  an  effective  supervision  of  the 
construction;  but  in  general  this  claim  is  not  true.  It  is  neither 
creditable  to  the  engineering  profession  nor  economical  to  the  mu- 
nicipalities to  leave  all  exact  knowledge  of  paving  matters  in  the 
hands  of  the  paving  contractors. 

452v  The  proper  length  of  the  guarantee  period  is  a  matter 
about  which  there  is  considerable  difference  of  opinion.  For 
asphalt  pavement  a  guarantee  for  five  years  is  quite  common, 
although  sometimes  a  fifteen-year  guarantee  is  required.  With 
stone  block,  brick  and  most  other  lorms  of  pavements  nine  months, 
or  at  most  a  year,  is  sufficient  to  reveal  any  serious  defect  of  ma- 
terial or  workmanship,  and  therefore  a  long  guarantee  is  not 
necessary. 

453.  MAINTENANCE  BY  CONTRACT.  As  stated  above  it  is 
common  to  require  a  so-called  guarantee  which  is  virtually  a  con- 
tract for  maintenance  for  the  specified  period.  Maintenance  by 
contract  is  justifiable  if  the  engineering  department  of  the  city  does 
not  possess,  or  can  not  reasonably  be  expected  to  obtain,  the 
information  necessary  in  repairing  the  pavement;  but  as  a  rule 
maintenance  by  contract  is  undesirable,  for  four  reasons:  1.  The 
contractor  has  no  control  over  the  streets,  and  the  repairs  required 
are  dependent  upon  the  restrictions  against  opening  the  pavements 
and  also  upon  the  regulations  for  keeping  the  streets  clean.  2.  It  is 
difficult  to  specify  beforehand  the  amount  and  the  nature  of  the 
repairs  that  may  be  required  by  the  ordinary  use  of  the  pavements, 
particularly  as  the  opening  of  new  streets  or  the  paving  of  others 


TEARIXG    UP    PAVEMENTS.  305 

may  materially  alter  the  amount  or  nature  of  the  traffic  on  any 
particular  pavement.  3.  It  is  impossible  to  determine  accurately 
the  condition  of  the  pavement  at  the  end  of  the  contract  period. 
4.  With  a  new  and  untried  material  it  is  impossible  to  determine 
what  is  a  reasonable  expense  for  maintenance. 

A  contract  for  maintenance  is  sometimes  defended  by  the 
property  holders  on  the  ground  that  thereby  some  one  is  secured 
who  is  admittedly  responsible  for  the  condition  of  the  pavement 
and  who  is  more  amenable  for  neglect  than  are  city  officials.  How- 
ever, if  the  city  officials  can  not  be  trusted  to  repair  the  pavements 
directly,  it  is  doubtful  whether  they  may  reasonably  be  expected 
to  supervise  the  repairs  to  be  made  by  the  contractor.  The 
choice  between  maintenance  by  contract  and  by  municipal  author- 
ities directly  will  usually  depend  upon  the  local  conditions. 

The  pavements  of  Paris.  France,  were  formerly  maintained 
by  contract,  but  are  now  maintained  by  the  city  directly. 

454.  TEARING  UP  PAVEMENTS.  The  most  serious  cause  of 
the  destruction  of  pavements  is  the  frequency  with  which  they 
are  torn  up  for  the  introduction  or  repair  of  underground  pipes, 
conduits,  etc.  No  pavement  has  been  introduced,  and  probably 
none  ever  will  be,  which  is  not  seriously  injured  by  being  torn  up. 
The  only  remedy  for  the  frequent  disturbance  of  pavements  is  the 
construction  of  a  subway  in  which  to  place  pipes,  wires,  etc.;  but 
it  is  doubtful  if  any  such  remedy  would  be  lasting,  for  the  streets 
are  continually  being  put  to  new  uses.  Formerly  it  was  thought 
sufficient  to  provide  for  water  and  gas  pipes  and  sewers ;  while  now 
conduits  are  required  for  telegraph,  telephone,  and  electric  light 
wires,  and  street-car  tracks  are  constructed  on  the  surface,  above 
the  surface,  and  below  the  surface,  and  in  some  cities  space  is 
required  for  pneumatic  tubes,  and  pipes  for  distributing  heat, 
compressed  air,  cold  and  hot  water,  etc. 

The  only  thing  that  can  be  done  is  to  reduce  the  opening  of  the 
pavements  absolutely  to  a  minimum,  and  then  to  take  the  utmost 
care  to  see  that  as  little  damage  as  possible  is  done  in  making  the 
opening  and  that  the  pavement  is  restored  in  the  best  way  possi- 
ble. It  is  stated  that  in  1896  in  New  York  City  a  quarter  of  a  mile 
of  trench  was  opened  for  each  mile  of  pavement,  and  in  addition 
there  was  an  opening  for  each  35  linear  feet  of  street.     The  year 


306  PAVEMENT   ECONOMICS.  [CHAP.  VIII. 

stated  was  about  an  average  for  those  immediately  before  and 
after. 

The  amount  of  money  spent  in  digging  up  the  streets  is  a  con- 
siderable item,  not  counting  the  interference  with  travel  and  busi- 
ness; but  the  expense,  being  distributed  among  various  interests, 
is  not  usually  sufficient  to  cause  any  one  company  to  re-construct 
its  system.  It  is  probable  that  the  interests  of  the  public  are  fre- 
quently sacrificed  to  the  interests  of  the  private  companies  using 
the  streets — usually  without  paying  for  the  privilege. 

Under  the  best  municipal  administrations  of  Europe  neither 
corporations  nor  individuals  are  permitted  to  disturb  the  pave- 
ments. All  removals  and  restorations  are  done  by  the  city's  own 
employees,  upon  the  deposit,  by  the  parties  who  require  the  streets 
to  be  opened,  of  a  sufficient  sum  to  cover  the  expense  of  each  piece 
of  paving  done,  at  a  fixed  price  per  yard  according  to  the  kind  of 
pavement.  Moreover,  interference  with  the  pavements  is  of  rare 
occurrence,  for  the  companies  having  pipes  underground  are  re- 
quired thoroughly  to  examine  and  reinstate  their  mains  and  ser- 
vices concurrently  with  the  paving  of  a  street,  due  notice  of  the 
execution  of  which  is  given  by  the  city. 


CHAPTER  IX. 
STREET   DESIGN. 

456.  From  the  point  of  view  of  future  needs — commercial, 
sanitary,  and  esthetic, —  it  is  unfortunate  that  cities  grow  up  by 
successive  additions  under  the  stimulus  of.  private  greed  and  real 
estate  speculation,  without  any  comprehensive  or  well  considered 
street  plan.  In  some  instances  — notably  Paris,  London,  and 
Boston, — vast  sums  have  been  spent  to  correct  what  might  have 
been  prevented  in  the  original  plan  of  the  streets.*  In  most  cities 
transformation — slow  and  expensive,  if  it  come  at  all — is  the  only 
remedy;  but  a  mended  article  is  never  as  good  as  one  well  made 
at  first. 

Unfortunately  there  are  few  cities  in  this  country  having  ade- 
quate regulations  governing  suburban  development  Municipal 
authorities  should  regulate  the  street  plan  of  subdivisions  and 
additions  so  as  to  secure  a  harmonious  whole,  and  particularly 
with  a  view  of  making  the  streets  continuous  and  to  afford  suitable 
channels  of  communication.  Where  such  regulations  do  not  exist, 
streets  will  be  laid  out  in  such  a  way  as  best  to  develop  the  par- 
ticular property,  regardless  of  the  interests  of  the  public.  Wash- 
ington City,  which  has  the  best  street  plan  of  any  American  city, 
has  been  disfigured  by  ill  planned  additions;  although  at  present 
stringent  rules  govern  the  width  and  the  arrangement  of  the  streets 
of  additions  and  subdivisions. 

457.  STREET  PLAN.  Since  an  engineer  is  occasionally  called 
upon  to  plan  a  city,  and  often  to  lay  out  additions  to  cities  and  vil- 
lages, the  various  street  plans  for  the  city  will  be  considered.  In  plan- 

*  For  example,  Paris  spent  $14,000,000  in  improving  the  Rue  de  Rivoli,  and 
London  $33,000,000  on  the  Strand  Improvement. 

307 


308  STREET    DESIGN".  [CHAP.   IX. 

ning  the  streets  of  a  city  three  objects  should  be  kept  in  mind  ; 
viz.:  (1)  the  subdivision  of  the  area  in  such  a  manner  as  to  give 
the  maximum  efficiency  for  business  or  residence  purposes;  (2) 
sufficient  accommodation  for  the  pedestrian  and  vehicular  travel 
on  the  streets;  and  (3)  good  drainage  and  easy  communication 
between  the  different  parts  of  the  city. 

458.  Size  of  Lots.  Owners  in  subdividing  property  are  anxious 
to  make  as  many  lots  as  possible;  and  in  some  other  respects 
small  lots  are  to  be  preferred.  It  is  desirable  to  make  the  lots  of 
such  a  size  that  few  of  them  will  be  subdivided,  as  clearness  of 
identity  is  maintained  by  always  referring  to  the  original  number 
in  transferring  or  assessing  the  lot.  A  frontage  of  25  feet  seems 
the  best.  This  width  is  suitable  for  business  purposes,  and  for 
residence  streets  two  or  more  lots  will  give  proper  grounds.  Busi- 
ness lots  are  sometimes  made  only  18  or  20  feet  wide,  but  25  feet* 
is  by  far  the  more  common. 

Lots  are  seldom  less  than  100,  nor  more  than  180,  feet  deep; 
and  usually  vary  from  100  to  150  feet.  A  lot  more  than  150  feet 
deep  is  objectionable,  because  of  the  temptation  to  build  unsightly 
residences  fronting  on  the  alley  and  because  of  the  difficulty  of 
keeping  a  deep  lot  in  good  sanitary  condition. 

459.  Size  of  Blocks.  With  a  rectangular  system  of  streets, 
the  blocks  are  preferably  long  and  narrow;  since  the  distance 
required  between  streets  in  one  direction  is  only  that  necessary 
to  give  the  proper  depth  of  lots,  while  in  the  other  direction  the 
streets  need  be  only  close  enough  to  provide  convenient  channels 
for  the  traffic. 

For  convenience,  especially  in  business  districts,  it  is  best  to 
have  an  alley  run  lengthwise  through  the  block.  The  alley  varies 
from  10  to  30  feet,  but  is  usually  from  16  to  20  feet. 

The  above  depth  of  lot  and  width  of  alley  makes  the  width 
of  the  block  220  to  330  feet.  The  length  of  the  block  will  depend 
upon  the  requirements  for  traffic  perpendicular  to  the  principal 
streets.  Sizes  of  blocks  vary  much  in  any  particular  city,  and 
still  more  between  different  cities.  The  following  are  the  dimen- 
sions of  typical  blocks  in  several  cities:  Boston,  220  X  400  ft.,  and 
100  X  550  ft.;  New  York,  200  X  900  ft.,  and  200  X  400  ft.;  Phila- 
delphia, 400  X  500  ft.,  and  500  X  800  ft.;  Washington,  400  X  600 


STREET  PLAN. 


309 


ft.,  and  300  X  800  ft.;  Montreal,  250  X  750  ft.;  Chicago,  300  X 
350  ft.,  and  300  X  500  ft. 

Fig.  81  is  given  to  illustrate  the  advantages  to  be  derived  from 
a  careful  study  of  the  best  size  of  blocks  and  of  the  most  advan- 
tageous arrangement  of  streets.  The  left-hand  side  of  the  dia- 
gram shows  the  typical  arrangement  of  streets  and  blocks  in  the 
residence  district  of  New  York  City,  the  shaded  portions  repre- 


Ftg.  81  — Improved  Arrangement  of  Streets  and  Blocks. 

senting  the  usual  buildings.  The  right-hand  side  shows  a  much 
superior  arrangement.*  The  three  center  blocks  of  the  present 
plan  comprise  an  area  of  720  X  800  feet,  and  contain  480,000  sq. 
ft.  of  building  area  and  96,000  sq.  ft.  of  streets,  and  in  the  corre- 
sponding area  of  the  proposed  plan,  there  are  481,000  sq.  ft.  of 
building  area  and  94.200  sq.  ft.  of  streets;  therefore  the  two  plans 

*  Proposed  by  Mr.  J.  F.  Harder,  in  Municipal  Affairs,  Vol.  2,  p.  41-44.    Reform 
Club,  New  York  City,  1898. 


310  STKEET    DESIGN.  [CHAP.   IX. 

give  substantially  the  same  area  for  buildings  and  for  streets.  In 
the  first  case  the  length  of  streets  is  1,600  feet,  in  the  second  1,520 
feet;  therefore  the  two  plans  have  practically  equal  light  and  air. 
The  proposed  arrangement  is  the  better  in  the  following  partic- 
ulars: 1,  number  of  corner  sites;  2,  accessibility  of  rear  entrances 
for  delivery  of  provisions,  coal,  etc.,  and  the  removal  of  garbage, 
ashes,  etc.,  and  in  case  of  fire;  3,  removal  from  the  street  of 
dangerous  and  cramped  cellar  entrances;  4,  removal  from  the 
main  or  primary  streets  of  the  loading  and  unloading  of  trucks; 
and  5,  increased  transportation  facilities  in  a  direction  perpendic- 
ular to  the  length  of  the  original  blocks. 

460.  Location  of  Streets.  In  planning  a  system  of  streets 
there  are  two  objects  that  should  be  carefully  considered;  viz.: 
the  drainage  and  easy  communication  between  the  different  sec- 
tions of  the  city.  Not  infrequently  these  elements  have  been 
overlooked  or  neglected.  The  surface  drainage,  the  sewerage  and 
the  traffic  must  follow  the  general  slope  of  the  land;  and  there- 
fore if  there  is  much  irregularity  of  contour  in  the  site,  a  location 
of  the  streets  with  reference  to  the  contours  will  afford  at  once  the 
best  drainiage  and  the  easiest  communication  between  different 
parts  of  the  city.  If  the  site  is  nearly  level,  the  relationship  be- 
tween the  slope  of  the  land  and  the  direction  of  the  streets  is  com- 
paratively unimportant;  but  the  arrangement  of  the  street  plan 
to  afford  the  greatest  facilities  for  communication  between  the 
different  parts  of  the  city  is  still  an  important  matter.  Therefore 
the  conclusion  is  thai  on  a  site  of  irregular  contour  the  streets 
should  be  located  with  reference  chiefly  to  the  topography,  and 
on  a  level  site  primarily  to  secure  the  most  direct  and  easiest 
intercommun  i  cation . 

461  Location  vrith  Reference  to  Topography.  Unfortunately 
in  this  country  our  very  desirable  rectangular  system  of  public 
land  survey  has  frequently  led  to  the  adoption  of  a  very  undesirable 
rectangular  system  of  streets  which,  though  convenient  for  dividing 
property  into  the  greatest  number  of  rectangular  lots  upon  which 
can  be  built  the  greatest  number  of  rectangular  buildings,  has 
little  else  to  recommend  it.  Surface  drainage,  sewerage  and  traffic 
should  follow  the  slope  of  the  country,  and  any  attempt  to  deviate 
from  this  becomes  a  serious  question  in  the  building  of  a  city  upon 


STREET   PEAK. 


311 


Ycenferof 
City 


Fig.  82. — Location  op  Streets  with  Reference  to  Contours. 


312  STREET    DESIGN.  [CHAP.   IX. 

any  but  nearly  level  ground.  The  streets  are  of  necessity  the 
drainage  lines  of  the  city  and  should  be  placed  in  the  natural  val- 
leys, and  the  failure  so  to  locate  the  streets  in  many  cities  where 
the  land  is  very  irregular  in  contour  has  led  to  great  expense  in 
the  construction  of  the  streets  and  of  a  system  of  storm-water 
sewers. 

The  upper  half  of  Fig.  82,  page  311,  shows  an  actual  case  of  a 
system  of  rectangular  streets  located  without  any  reference  to 
the  topography  of  the  site;  and  the  lower  half  of  the  same  dia- 
gram shows  a  proposed  arrangement  *  that  would  save  much  ex- 
pense in  grading  the  streets  and  at  the  same  time  give  a  quick  en- 
trance into  the  center  of  the  city,  and  also  give  long  easy  grades 
from  the  heart  of  the  city  to  the  higher  outlying  district. 

462.  Location  with  Reference  to  Directness  of  Communication. 
There  are  three  distinct  general  plans  for  city  streets  with  refer- 
ence to  directness  and  ease  of  communication. 

463.  One  consists  of  a  system  of  parallel  streets  crossing  a  sim- 
ilar system  at  right  angles.  This  is  often  called  the  checker-board 
system,  but  more  properly  the  rectangular  system,  since  the  blocks 
are  not  necessarily  squares.  This  arrangements  gives  the  maxi- 
mum area  for  blocks,  and  also  furnishes  blocks  of  the  best  form 
for  subdivision  into  lots.  The  rectangular  system  is  the  most 
common,  and  has  its  most  marked  exemplification  in  Philadelphia. 

464.  A  second  arrangement  of  streets  consists  of  the  rectangu- 
lar system  with  occasional  diagonal  streets  along  the  lines  of  maxi- 
mum travel.  This  system  was  employed  by  L'Enfant  in  planning 
the  city  of  Washington.  Fig.  S3  shews  a  portion  of  that  city.  To 
a  limited  degree,  the  same  plan  was  adopted  in  laying  out  the  city 
of  Indianapolis,  which  has  four  broad  diagonal  avenues  converging 
to  a  circular  park  in  the  center.  These  two  are  the  only  cities  of 
any  importance  in  which  this  system  was  adopted  in  advance  of 
building.  This  system  is  usually,  but  somewhat  improperly, 
called  the  diagonal  system. 

The  chief  advantage  of  the  diagonal  street  is  the  economy 
due  to  the  saving  of  distance  by  traversing  the  hypothenuse  instead 
of  the  two  sides  of  a  right  triangle.  In  Rome,  London,  Paris,  and 
in  numerous  other  smaller  places  in  Europe,  whole  districts  have 


*By  W.  D.  Elder  in  Proc.  Michigan  Engineering  Society,  1898,  p.  52. 


STREET    PLAN~. 


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314  STREET   DESIGN.  [CHAP.   IX. 

been  razed  to  make  way  for  new  streets  to  serve  as  arteries  for 
increased  traffic. 

A  second,  and  by  no  means  an  unimportant,  advantage  of  the 
combination  of  the  diagonal  and  the  rectangular  system  is  the 
open  squares  and  spaces  so  grateful  to  the  eye  and  of  no  little 
sanitary  value  in  compactly  built  cities.  New  York  City  has 
recently  been  spending  a  million  dollars  a  year  to  create  such  spaces 
by  purchasing  the  land  and  demolishing  the  buildings. 

Although  the  diagonal  avenue  occupies  ground  that  might 
otherwise  be  used  for  building  purposes,  there  is  a  compensating 
advantage  in  the  greater  length  of  street  front  obtained.*  In 
many  cases  the  total  cost  of  cutting  diagonal  streets  through 
built-up  districts  has  been  paid  by  the  increased  value  of  the  prop- 
erty on  and  near  the  street  thus  opened  up. 

465.  The  third  arrangement  of  city  streets  is  the  ring  or  con- 
centric plan,  which  is  very  popular  in  Europe.  The  most  noted 
example  is  Vienna  with  its  Ring-strasse  (ring  street)  within  and  its 
Gurtel-strasse  (girdle  street)  without.  The  former  is  187  feet  wide 
and  encircles  the  public  buildings  and  the  leading  houses  of  business 
and  amusement.  The  enclosed  network  of  streets  intersect  the 
Ring-strasse  at  forty  points,  and  outward  from  it  extend  fifteen 
main  radial  avenues. 

466.  WIDTH  OF  STREETS.  The  width  of  city  streets  is  impor- 
tant ,ori  account  of  its  influence  upon  the  ease  with  which  traffic 
may  be  conducted  and  also  because  of  its  effect  upon  the  health 
and  comfort  of  the  people  by  determining  the  amount  of  light  and 
air  which  may  penetrate  into  thickly  built-up  districts.  The 
streets  of  nearly  all  large  cities  are  too  narrow,  being  crowded 
and  dark.  A  more  liberal  policy  in  planning  streets  would  prob- 
ably be  of  pecuniary  advantage,  since  there  is  usually  an  enhanced 
financial  value  due  to  wide  streets.  A  lot  100  feet  deep  on  a 
street  80  feet  wide  is  usually  more  valuable  than  a  lot  110  feet  deep 
on  a  street  60  feet  wade;  that  is  to  say,  within  reasonable  limits 
land  is  usually  more  valuable  in  the  street  than  on  the  rear  of  the 
lot.  Wide  streets  are  especially  needed  where  they  are  bordered 
by  high  buildings  or  are  to  carry  street  railway  lines. 

♦For  a  discussion  of  this  phase  of  the  subject,  see  an  article  by  L.  M.  Haupt  in 
Jour.  Franklin  Inst.,  Vol.  103,  p.  252. 


WIDTH    OF    STREETS.  315 


In  order  properly  to  accommodate  the  traffic  in  business  dis- 
tricts of  cities  of  considerable  size,  a  street  should  have  a  width  of 
100  to  140  feet,  the  whole  of  it  being  used  for  roadway  and  side- 
walks; while  residence  streets  in  a  city  of  considerable  "size,  where 
the  houses  are  set  out  to  the  property  line  and  stand  close  to- 
gether, should  have  a  width  of  60  to  80  feet.  Although  it  is  advan- 
tageous to  have  a  wide  street,  it  is  not  necessary,  nor  even  desir- 
able, that  the  whole  width  be  paved;  the  central  portion  may  be 
paved,  a  strip  on  either  side  being  reserved  for  grass  plats.  The 
width  of  the  pavement  should  be  adjusted  to  the  amount  of  traffic, 
which  varies  greatly  accordingly  as  the  street  is  a  business  street, 
a  thoroughfare,  or  an  unfrequented  residence  street. 

The  width  of  the  streets  in  different  cities  varies  greatly.  In 
the  older  places  in  New  England  and  the  Central  States,  many 
of  the  streets  are  only  30  to  40  feet  wide;  but  in  the  West  a  street 
is  seldom  less  than  60  to  66  feet  wide.  In  both  regions  the  prin- 
cipal streets  are  often  80  to  100  feet  wide,  and  in  many  of  the  larger 
cities  the  boulevards  and  great  avenues  are  150  to  180  feet.  The 
main  avenues  in  Washington  are  160  feet  wide,  in  New  York  135, 
and  in  Boston  180  feet. 

At  present  the  regulations  governing  the  width  and  the  arrange- 
ments of  additions  and  subdivisions  of  Washington,  a  city  which 
has  the  best  street  plan  of  any  in  America  (see  §  464),  are:  "No 
new  street  can  be  located  less  than  90  feet  in  width,  and  the  lead- 
ing avenues  must  be  at  least  120  feet  wide.  Intermediate  streets 
60  feet  wide,  called  places,  are  allowed  within  blocks;  but  full- 
width  streets  must  be  located  not  more  than  600  feet  apart." 

467.  AREA  OF  STREETS.  The  proportion  of  the  area  of  the 
city  devoted  to  streets  varies  greatly,  particularly  between  the 
older  and  the  newer  cities.  The  following  is  the  per  cent  of  street 
area  in  a  few  extreme  cases  of  American  cities :  * 

Minimum  Street  Area.  Maximum  Street  Area. 

1.  Taunton,  Mass 3.20  per  cent         Duluth,  Minn 86.7  per  cent 

2.  Worcester,  Mass 5.43    "      "  Dallas,  Tex 78.3    "       " 

3.  Binghamton,    N.    Y.  7.55    "      "  Denver,  Colo 73.9    "      " 

4.  Philadelphia,  Pa 8.42    "      "  Indianapolis,  Ind .  .   56.4    "      " 

5.  Boston,  Mass 8.76    "      "  Washington,  D.  C.  43.5    "      " 

6.  Lowell,  Mass 8.92    "      "  Davenport,  la 42.1    "      " 

7.  Fall  River,  Mass....   9.17    "      "  Evansville,  Ind. ...   40.8    "      " 


*  Census  Bulletin  No.  100— July  22,  1891,— p.  16. 


((        (I 


316  STREET   DESIGN.  [CHAP.  IX. 

The  area  devoted  to  streets  and  alleys  in  a  few  of  the  principal 
cities  of  the  world  is  as  follows : 

Area  of  Streets  and  Alleys. 

1.  Washington 54  per  cent 

2.  Vienna 35    "      " 

3.  New  York  City 35 

4.  Philadelphia 29 

5.  Boston  26 

6.  Berlin 26    "      " 

7.  Paris 25    "      " 

468.  Width  of  Pavement.  It  is  wise  to  make  the  streets 
of  residence  districts  of  liberal  width  for  sanitary  and  aesthetic 
reasons;  and  also  because  the  future  of  the  street  can  not  be  cer- 
tainly foreseen, — the  residence  street  may  become  a  business 
street,  or  an  unfrequented  street  a  thoroughfare.  However,  it  is 
not  necessary  that  the  whole  width  should  be  devoted  to  wheel- 
ways  and  sidewalks,  particularly  in  small  cities.  A  grass  plat 
between  the  sidewalk  and  the  pavement,  in  which  shade  trees  are 
set  (§  491),  adds  to  the  beauty  of  the  street  and  to  the  comfort 
of  the  residents  by  removing  the  houses  farther  from  the  noise 
and  dust  of  the  pavement.  The  grass  plat  or  parking  also  affords 
an  excellent  place  in  which  to  place  water  and  gas  pipes,  telephone 
and  electric-light  conduits,  etc.  In  large  cities  where  the  street 
front  is  built  up  solid  with  houses  of  several  stories,  it  may  be 
necessary  to  dispense  with  the  grass  plat,  and  to  devote  the  entire 
street  to  sidewalks  and  roadway. 

It  is  universally  admitted  that  pavements  are  desirable;  but 
often,  owing  to  the  unwillingness  of  at  least  some  of  the  people  to 
pay  for  them,  it  is  difficult  to  secure  them.  Except  for  the  cost, 
the  wider  the  pavement  the  better;  but  length  is  more  valuable  than 
width.  An  excessive  width  is  a  needless  expense,  and  delays  or 
prevents  the  getting  of  any  pavement  at  all;  hence  one  help  to- 
ward securing  pavements  is  to  make  the  pavement  only  wide 
enough  to  accommodate  the  traffic.  Not  infrequently  the  pave- 
ments of  suburban  and  residence  streets  are  needlessly  wide.  A 
narrow  pavement  not  only  costs  less  to  construct,  but  also  costs 
less  to  clean  and  sprinkle;  while  the  cost  of  maintenance  depends 
chiefly  (or,  with  a  pavement  not  subject  to  natural  decay,  wholly) 
upon  the  amount  of  traffic,  and  hence  is  nearly  (or  entirely)  inde- 
pendent of  the  width. 


WIDTH   OF   PAVEMENTS.  317 

469.  Without  Car  Track.  A  width  of  18  feet  affords  sufficient 
room  for  a  vehicle  to  pass  when  another  is  standing  on  each  side 
of  the  pavement — a  rare  occurrence; — and  therefore  it  appears 
that  a  pavement  18  feet  wide  is  sufficient  for  the  less  frequented 
residence  streets.  The  only  objection  to  a  very  narrow  pave- 
ment is  the  difficulty  of  turning  a  team  in  such  a  street.  The 
seriousness  of  this  objection  depends  upon  the  construction  of 
the  vehicle.  Many  delivery  wagons,  express  wagons,  etc.,  may 
be  turned  on  an  18-foot  pavement.  If  occasionally  a  vehicle  is 
compelled  to  go  to  the  corner  to  turn,  or  even  to  drive  around  the 
block,  the  inconvenience  is  not  very  serious,  and  is  so  infrequent 
as  not  to  justify  any  considerable  expense  to  prevent  it.  A  width 
of  20  to  24  feet  is  probably  sufficient  for  a  majority  of  residence 
and  suburban  streets.  When  a  residence  street  is  an  artery  of 
travel,  it  may  be  necessary  to  make  the  pavement  wider  than  stated 
above.  In  a  number  of  cities,  there  has  been  a  marked  tendency 
in  recent  years  to  reduce  the  width  of  pavements  on  residence 
streets. 

Thirty  feet  affords  sufficient  room  for  two  vehicles  to  pass  each 
other  where  two  others  are  standing  at  the  curb;  and  therefore 
this  width  of  pavement  is  ample  for  business  streets  in  small  places. 
On  a  narrow  business  street  it  may  be  necessary  to  curtail  the 
width  of  the  pavement  to  prevent  the  sidewalk  space  from  being 
unduly  encroached  upon. 

In  many  of  the  cities  the  width  of  the  pavement  is  uniformly 
a  fractional  part  of  the  total  width  of  the  street,  regardless  of  the 
needs  of  traffic.  In  many  cities,  both  American  and  European, 
the  pavement  is  three  fifths  or  60  per  cent  of  the  width  of  the  street. 
In  New  York  City  and  Brooklyn  the  rule  seems  to  be  to  make  the 
pavement  half  the  width  of  the  street.  In  Washington  City  there 
is  no  hard-and-fast  rule,  but  the  following  is  the  usual  relation: 
on  streets  60  feet  wide  or  less,  the  pavement  is  25  feet  or  40  per  cent 
of  the  width  of  the  street;  on  streets  from  60  to  90  feet  wide,  the 
pavement  is  25  to  35  feet,  or  40  per  cent;  and  for  streets  130  to 
160  feet  wide,  the  pavement  is  40  to  50  feet,  or  30  per  cent. 

470.  With  Car  Track.  For  a  residence  street  containing  a  car 
track,  the  minimum  width  permissible  is  28  feet,  which  will  allow 
a  car  to  pass  with  a  vehicle  on  each  side  of  the  track.     In  Brook- 


318  STREET   DESIGN.  [CHAP.  IX. 

lyn  a  great  many  streets  only  34  feet  wide  between  curbs  contain  a 
double  line  of  street-car  tracks,  which  leaves  a  space  of  only  9J 
feet  between  the  track  and  the  curb.  This  is  astonishingly  small, 
but  seems  to  do  fairly  well. 

On  a  business  street  containing  a  car  track,  it  is  wise  to  make 
the  pavement  wide  enough  to  permit  a  vehicle  to  pass  between 
the  car  while  another  vehicle  stands  at  the  curb.  This  will  require 
about  48  feet.  If  the  street  is  too  narrow  to  permit  this  width 
of  pavement  and  also  the  proper  width  of  sidewalks,  only  one 
track  should  be  allowed  in  the  street;  if  a  double  track  is  neces- 
sary, the  cars  should  be  required  to  make  the  return  trip  by  another 
street. 

At  Rochester,  N.  Y.,  the  car  tracks  on  residence  streets  are 
located  on  the  parking  at  the  side  of  the  street.  This  is  an  un- 
usual arrangement,  but  it  possesses  some  advantages.  1  It 
separates  the  vehicular  and  car  traffic,  and  prevents  mutual  inter- 
ference. 2.  It  permits  a  narrower  pavement.  3.  It  prevents 
disturbance  of  the  pavement  to  repair  the  car  track.  4.  It  lessens 
the  danger  of  a  passenger's  being  struck  by  another  car  or  a  vehicle 
in  leaving  a  car.  The  objection  to  this  arrangement  is  that  it 
interferes  with  the  grade  of  the  driveways  to  private  grounds.    . 

471.  STREET  GRADES.  The  fixing  of  street  grades  is  one  of 
the  most  important  functions  of  municipal  engineering,  since  the 
grade  system  of  the  streets  is  the  foundation  of  all  municipal  engi- 
neering matters.  The  grades  should  be  established  before  the 
sewer  system  is  planned;  and  if  they  are  established  before  the 
property  is  improved,  the  problem  is  comparatively  simple,  since 
they  may  be  laid  chiefly  with  reference  to  obtaining  desirable 
gradients  for  the  street  within  proper  limits  of  cost.  But  when 
buildings  have  been  erected,  sidewalks  constructed,  and  trees 
planted,  it  is  frequently  extremely  difficult  to  secure  grades  which 
will  harmonize  the  various  and  conflicting  interests. 

472.  Elements  Governing  Grades.  The  grades  necessarily 
depend  mainly  upon  the  topography  of  the  site ;  but  in  general  the 
determination  of  the  proper  grade  for  a  street  requires  the  consid- 
eration of  the  following  elements:  (1)  the  drainage,  (2)  the  cost  of 
earthwork  (3)  the  acccommodation  of  the  traffic,  (4)  the  effect  upon 
the  abutting  property,  and  (5)  the  general  appearance  of  the  street. 


STREET   GRADES.  319 


473.  Drainage.  The  streets  are  the  natural  drainage  channels 
of  the  city;  the  lots  must  drain  into  them,  and  the  house  must 
drain  into  the  sewers  placed  in  the  streets.  When  no  storm- 
water  sewers  are  to  be  constructed,  the  grades  become  very  im- 
portant, since  the  streets  must  provide  for  the  surface  drainage 
of  the  city,  and  particular  consideration  must  be  given  to  relative 
grades  and  gutter  capacities  in  order  to  prevent  the  excessive 
concentration  of  storm  water  at  the  lower  levels  and  to  provide 
for  its  proper  distribution  and  disposal. 

474.  Cost  of  Earthwork.  Not  infrequently  the  cost  of  making 
the  excavations  and  embankments  is  given  undue  weight.  The 
balancing  of  cuts  and  fills  is  often  properly  a  controlling  element 
in  country  road  construction,  but  it  should  have  relatively  little 
weight  in  determining  the  grades  of  city  streets.  The  expense 
for  earthwork  is  incurred  once  for  all,  and  a  few  hundred  dollars 
more  or  less  is  usually  unimportant  in  comparison  with  the  ex- 
pense of  maintaining  the  street  surface  and  the  drainage  system, 
and  the  cost  of  conducting  traffic  over  the  grades,  and  also  in 
comparison  with  a  better  general  appearance  of  the  street. 

475.  Accommodation  of  Traffic.  The  question  often  is  whether 
or  not  to  secure  ease  of  traction  at  the  expense  of  increased  cost  of 
construction.  The  discussion  in  Chapter  II,  §  62-86,  sheds  a  little 
light,  and  only  a  little,  as  to  the  proper  method  of  answering  this 
question.  Apparently  engineers  are  inclined  to  overestimate  the 
disadvantage  to  traffic  of  a  slight  grade  Practical  experience  has 
demonstrated  that  there  is  not  much  difference  in  effect  upon  the 
cost  of  transportation  between  level  roads  and  those  having  grades 
of  2  or  3  per  cent  unless  such  grades  are  very  long  or  have  an 
unusually  smooth  and  well-kept  surface, 

476.  Effect  upon  Abutting  Property.  The  private  interests  of 
the  property  holder  should  be  carefully  considered;  although  it 
is  frequently  impossible  to  establish  proper  grades  without  injury 
to  the  adjoining  property.  The  general  question  is  how  far  private 
interests  should  be  sacrificed  to  the  general  good.  It  is  better  that 
the  city  or  the  other  residents  on  the  street  should  pay  the  owner 
damages  than  that  lasting  detriment  should  be  done  to  the  appear- 
ance of  the  street  or  to  the  traffic. 

477.  General  Appearance.     Some  attention  should  be  paid  to 


3W  STREET   DESIGN".  [CHAP.   IX. 

the  appearance  of  a  longitudinal  view  of  the  pavement.  It  is  de- 
sirable that  the  longitudinal  grade  be  not  changed  so  frequently 
as  to  give  the  street  a  wavy  appearance.  Further,  the  transverse 
grades  at  street  intersections  and  on  side  hills  should  be  so  arranged 
as  not  to  produce  a  confused  appearance  in  looking  along  the  street. 
The  grades  of  the  streets,  both  longitudinal  and  transverse,  have  a 
material  effect  upon  the  general  appearance  and  beauty  of  the 
city. 

478.  Maximum  Grade.  In  a  general  way  the  principles  gov- 
erning the  determination  of  the  permissible  maximum  grade  of  a 
city  street  are  the  same  as  for  a  country  road,  i.  e.,  it  is  a  question 
between  the  cost  of  operation  on  the  one  hand  and  the  cost  of 
construction  and  maintenance  on  the  other,  except  that  for  a 
country  road  the  cost  of  construction  is  chiefly  the  cost  of  moving 
the  earth,  while  for  a  city  street  the  cost  of  construction  should 
also  include  the  effect  upon  abutting  property  of  high  embank- 
ments or  deep  excavations,  and  except  further  that  usually  in 
the  city  heavy  loads  can  take  a  circuitous  route  and  avoid  the 
maximum  grade  entirely.  In  determining  the  maximum  grade 
for  a  street,  the  fact  should  not  be  overlooked  that  the  smoother 
the  pavement  the  more  serious  is  a  steep  grade. 

For  a  general  discussion  of  the  relationship  between  cost  of 
construction  and  cost  of  operation  as  affecting  the  maximum 
grade,  see  Chapter  II,  Road  Location — §  71. 

479.  In  the  Borough  of  Manhattan,  New  York  City,  are  some 
business  streets  having  grades  as  steep  as  6  per  cent,  and  a  num- 
ber of  residence  streets  have  10  per  cent  grades,  and  some  have 
grades  of  12,  15  and  18  per  cent.  Brooklyn,  N.  Y.,  has  4  per  cent 
grades  on  business  streets  and  12  on  residence  ones.  A  number 
of  cities  have  maximum  grades  on  paved  streets  of  20  per  cent — for 
example,  Worcester,  Mass.,  Syracuse,  N.  Y.,  Borough  of  Rich- 
mond, New  York  City,  and  Pittsburg,  Pa.  Burlington.  Iowa,  has 
an  80-foot  street  with  a  24  per  cent  grade  up  which  is  laid  a 
zigzag  brick  pavement  18  feet  wide  having  a  maximum  grade  of 
14 J  per  cent  with  a  minimum  radius  of  the  inside  curb  of  16  feet. 

For  a  discussion  of  the  maximum  grade  for  each  kind  of  pave- 
ment, see  the  heading  Maximum  Grades  in  the  chapter  treating 
that  particular  pavement. 


STREET    GRADES.  321 


It  is  usually  considered  that  a  grade  steeper  than  15  per  cent 
is  impracticable  and  dangerous  even  for  light  traffic;  and  there- 
fore if  this  grade  can  not  be  obtained,  the  street  should  be  divided 
into  two  parts  separated  by  a  terrace  or  stone  wall,  each  portion 
being  entered  only  at  its  intersection  with  the  cross  street.  A 
10  per  cent  grade  is  usually  considered  prohibitive  for  heavy  loads; 
and  5  or  6  per  cent  is  considered  the  limit  on  business  streets. 

480.  The  selection  of  the  proper  pavement  for  the  maximum 
grade  is  a  matter  of  great  importance.  It  is  usually  held  that  sheet 
asphalt  should  not  be  laid  on  grades  steeper  than  2  to  3  per  cent, 
although  it  has  often  been  laid  on  6  or  7  per  cent  grades,  and  in 
one  instance  on  a  17  per  cent  grade  (see  §  676).  Brick,  or  hard 
sandstone,  or  granite  may  be  used  upon  the  maximum  grade. 
The  sandstone  and  the  granite  blocks  should  be  narrow  and  should 
be  of  a  quality  that  does  not  wear  smooth.  It  has  been  recom- 
mended to  chamfer  the  corners  of  rectangular  stone  or  wood  blocks 
when  laid  upon  steep  grades,  to  give  the  horses  a  gocd  foot-hold; 
but  it  is  at  least  doubtful  whether  the  benefit  of  a  good  footing 
is  not  neutralized  by  the  increased  tractive  resistance.  The  joints 
should  be  filled  with  tar  or  hydraulic  cement. 

481.  Minimum  Grade.  The  street  surface  should  have  enough 
longitudinal  slope  to  drain  its  surface  well.  For  a  discussion  of 
the  minimum  grade  permissible  with  macadam — a  material  much 
used  for  city  pavements  as  well  as  for  country  roads, — see  §  86. 
With  a  smooth  and  impenetrable  pavement  no  ruts  will  be  formed, 
and  hence  the  determination  of  the  minimum  permissible  grade 
is  mainly  a  question  of  the  grade  of  the  gutter.  If  the  drainage 
is  carried  away  by  under-ground  storm-water  sewers,  the  street 
may  be  perfectly  level  longitudinally,  since  the  necessary  grade 
for  the  gutters  may  be  obtained  by  making  them  deeper  as  they 
approach  the  inlet  to  the  sewer.  For  a  further  discussion  of  this 
phase  of  the  subject,  see  Grade  of  Gutter — §  505. 

If  it  is  inexpedient  to  vary  the  depth  of  the  gutter  (§  504)  or 
to  increase  the  grade  by  constructing  additional  inlets  and  catch 
basins,  it  is  necessary  to  secure  the  proper  slope  for  the  gutter  by 
inserting  a  summit  in  the  street  solely  for  drainage  purposes — . 
usually  referred  to  as  an  accommodation  summit.  However,  it 
is  undesirable  that  there  should  be  frequent  changes  in  the  grade, 


322 


STREET   DESIGK. 


[CHAP.  IX. 


as  they  give  the  pavement  an  unpleasant  wavy  appearance  when 
one  looks  along  the  street. 

482.  Grades  at  Street  Intersections.  One  of  the  most  impor- 
tant parts  of  the  establishment  of  a  system  of  street  grades  is  the 
arrangement  of  the  grades  at  street  intersections.  It  is  a  common 
practice  to  establish  only  the  grade  of  the  intersection  of  the  center 
lines  of  the  streets;  but  this  has  often  resulted  in  much  confusion 
in  determining  the  grade  for  the  corners  of  the  curbs,  particularly 
where  the  two  streets  have  considerably  different  grades.  For 
example,  in  Fig.  84  assuming  (for  the  present  at  least)  that  the  curb 


A| 


f ZO' 

I 

! 
It 


**~/0 


WW 


Sj 


■gr "" 


90.20 


Cuffr 


Cevfer  ///?e  ofJrreet. 


do*/?  { _____ 

C 


Fig.  84  — Grade  of  Curb  at  Street  Intersection. 


is  to  be  at  the  same  elevation  as  the  center  of  the  street  opposite, 
the  elevation  of  the  corner  of  the  curb,  D,  as  computed  from  the 
grade  of  C  B  is  90  20  ft.;  while  the  elevation  of  the  same  point  as 
computed  from  the  grade  of  B  A  is  91.20  ft. — a  difference  of  1.0 
foot.  To  obviate  this  source  of  confusion,  the  elevation  of  each 
corner  of  the  curb  and  also  of  the  intersections  of  the  center  lines 
should  be  established. 

A  similar  confusion  occurs  in  attempting  to  compute  the  elevation 
of  the  corner  of  the  property,  from  the  grade  of  the  corner  of  the 
curb.  For  example  in  Fig.  85,  assuming  that  the  grade  of  the  top 
of  the  curb  is  the  same  as  that  of  the  center  of  the  street,  and  assum- 
ing that  the  sidewalk  has  a  downward,  slope  away  from  the  prop 
erty  of  0.24  inch  per  foot  (2  per  cent),  and  also  assuming  that  the 
grade  of  the  corner  of  the  curb,  D,  has  been  established  as  80.00, 


STREET    GRADES. 


323 


then  the  elevation  of  the  corner  of  the  property,  G,  as  computed 
from  the  grade  of  the  curb  D  E  is  80.30  feet,  while  the  elevation  of 
the  same  point  computed  from  the  grade  of  the  curb  D  F  is  80.80 
feet. 

Some  engineers  advocate  the  establishment  of  the  grade  of  the 
corner  of  the  property  and  the  determination  of  the  grades  of  the 
curb  and  of  the  street  therefrom;  while  others  advocate  establish- 


Fig.  85. 


E        « /tdo/r/? 

-Grade  of  Property  at  Street  Intersections. 


ing  the  grade  of  the  corner  of  the  curb  and  from  that  determining 
the  grade  of  the  corner  of  the  property  and  also  of  the  center  of 
the  street  intersection.  To  be  legal  the  grade  must  be  fixed  by 
ordinance.  The  courts  generally  hold  that  the  " grade"  is  the 
top  of  the  pavement  in  the  center  of  the  street;  and  therefore  it 
is  necessary  to  establish  by  ordinance  the  grade  of  the  center  of  the 
street  intersection.  Further,  to  prevent  misapprehension  and  error 
in  computing  the  elevation  of  the  corners  of  the  curbs,  and  also  to 
save  the  labor  of  computing  them  anew  each  time  a  lot  is  to  be 
surveyed,  it  is  wise  to  establish  also  the  grade  of  the  corner  of  the 
curb.  The  ordinance  should  distinctly  state  the  method  to  be  em- 
ployed in  computing  the  auxiliary  grades,  i.  e.,  the  grade  of  the 
sidewalk  and  of  the  corner  of  the  property.  Often  the  grades  are 
established  for  only  one  street  without  due  consideration  of  the 
intersecting  street;  and  then  when  the  second  street  is  improved, 
the  result  is  confusion,  disputes,  and  sometimes  suits  for  damages. 

483.  When  the  rate  of  grade  of  both  streets  is  small,  it  is  desir- 
able that  the  entire  street  intersection  from  property  line  to  prop- 
erty line,  should  be  level,  a  condition  which  permits  the  continua- 
tion of  the  section  of  each  roadway  until  they  intersect,  makes  the 


324 


STREET   DESIGN". 


[CHAP.   XX. 


top  of  the  curb  at  the  four  corners  of  the  same  elevation ,  and  also 
allows  the  sidewalks  at  the  corners  to  be  level.  That  is  to  say,  in 
Fig.  86;  the  four  points  marked  b  and  all  the  points  marked  a  are 


1 

a 

a 

a 

a 

1 

a 

J> 

*y-a 

% 

f 

,       a 

* 

a 

a 

a 

mmsk 

1 

1 

Fig.  86.— Grade  at  Level  Street  Intersection. 


in  the  same  horizontal  plane.     Each  street  has  its  full  crown  on  the 
line  b  b,  and  consequently  there  is  a  slight  rise  from  b  to  c. 

Where  either  or  both  streets  have  much  inclination,  it  may  not 
be  wise  to  flatten  out  the  intersection,  and  thereby  increase  the 
grade  on  the  remainder  of  the  street.  Under  these  conditions, 
the  best  arrangement  of  the  intersections  is  a  matter  requiring 
careful  study  and  is  one  upon  which  there  is  much  diversity  of  opin- 
ion. If  steep  grades  are  continued  across  intersections,  they 
introduce  side  slopes  in  the  streets  thus  crossed,  which  are  trouble- 
some and  possibly  dangerous — particularly  to  vehicles  turning 
the  upper  corners.  Such  intersections  are  also  objectionable  on 
account  of  the  difficulty  of  properly  caring  for  the  storm  water. 
In  residence  districts  it  is  usual  to  make  the  intersection 
•'level  from  curb  to  curb";  that  is,  in  Fig.  86,  the  four  points 
marked  b  are  in  the  same  horizontal  plane.  The  level  places 
serve  as  breathing  places,  and  lessen  the  danger  of  collision  at 
the  intersection.  However,  if  the  street  has  a  considerable  grade, 
a  level  intersection  appears  to  have  a  decided  pitch  toward  the 
hill,  which  gives  the  street  an  unpleasing  appearance;  and  there- 
fore under  these  conditions,  it  is  better  to  apply,  even  in  residence 
districts,  the  principle  of  the  succeeding  paragraph  and  give  the 
intersection  a  moderate  inclination  down  hill.     If  the  intersection 


STREET    GRADES. 


325 


has  only  enough  inclination  to  seem  level,  the  general  appearance 
of  a  series  of  such  intersections  is  pleasing,  having  the  effect  of  a 
succession  of  terraces. 

The  following  rule  *  for  adjusting  the  grades  at  street  inter- 
sections is  frequently  employed  and  apparently  is  the  most  com- 
plete of  any  that  has  been  proposed.  "  In  the  business  section  all 
the  street  grades  of  3  per  cent  or  less  should  be  continued  un- 
broken over  the  intersection;  and  streets  having  a  steeper  grade 
than  3  per  cent  should  have  an  intersection  of  3  per  cent  between 
curb  lines.  The  grade  of  the  curb  between  the  other  curb  line  ana 
the  property  line  should  in  no  case  be  greater  than  8  per  cent. 
The  grade  at  the  corner  of  the  property  should  be  determined  by 
adding  to  each  of  the  grades  of  the  curb  opposite  the  corner,  the 
rise  of  the  sidewalk  and  taking  the  mean."     Fig.  87  shows  the  sev- 


«?jv 


it- 


9.04' 


dorrs? 


42' 


/0.96  %\^/222 


'2% 


la 


dosrs? 


7-7$, 


mu 


/<?' 


874 


J0.00 


&02     ft*  928 
42'  


/Q72 


/2 


/0.24  W 


Fig.  87. — Grades  at  Inclined  Street  Intersection. 

eral  elevations  of  a  street  intersection  adjusted  according  to  the 
above  rules,  assuming  the  transverse  slope  of  the  sidewalk  to  be 
2  per  cent  (practically  \  inch  per  foot — the  usual  value). 

The  difficulty  of  adjusting  the  grades  at  an  intersection  is 
considerably  increased  if  the  two  streets  do  not  intersect  at  right 
angles.  It  is  impossible  to  formulate  any  general  rule,  since  each 
case  must  be  decided  according  to  the  local  conditions;  and  since 


♦Proposed  by  Messrs  Rudolph  Hering  and  Andrew  Rosewater  for  the  streets 
of  Duluth,  Minn.,  in  a  report  dated  March  7,  1890.  Published  in  the  Report  of 
Board  of  Public  Works,  Duluth,  Minn.,  for  1890,  and  re-published  in  Engineering 
News,  Vol.  25,  p.  148-49,  and  also  in  Engineering  Record,  Vol.  22,  p.  53. 


326 


STREET   DESIGN. 


[CHAP.-  IX. 


close  observation  and  good  judgment  are  required  to  secure  a 
reasonably  satisfactory  adjustment.* 

484.  Notice  that  if  either  street  has  a  grade  and  is  carried  past 
the  intersection  nominally  unchanged,  the  area  between  the  four 
curb  corners  and  that  immediately  adjacent  will  be  a  warped 
surface.  For  example,  in  Fig.  88,  if  the  street  S  has  a  descent 
as  indicated  and  the  street  W  is  level,  and  the  unchanged  crowns 
of  the  street  intersect  at  C,  the  area  marked  w  must  be  raised 
to  carry  the  upper  side  of  the  street  W  over  the  intersection,  and 
the  portions  marked  v  must  be  raised  to  carry  the  street  S  over 
the  lower  side  of  the  street  W.  If  the  grade  of  either  street  is 
small,  this  adjustment  can  be  made  by  " warping  in,"  or  "bon- 
ing in  "  the  surface  for  a  short  distance  by  the  eye. 

485.  Vertical  Curves  at  Grade  Intersection.  It  is  frequently 
claimed  that  the  grade  should  be  carried  straight  through  from 
street  intersection  to  street  intersection,  i.  e.,  that  the  grade  should 
not  be  broken  in  the  block.  Apparently  the  reason  for  this  prac- 
tice is  the  claim  that  a  break  of  grade  between  streets  is  unsightly. 
As  usually  put  in,  the  angle  of  intersection  is  simply  rounded  off 
a  little  by  eye;  and  if  the  change  of  grade  is  considerable,  the 
appearance  is  not  good.     A  change  of  grade  in  the  block  is  nowise 


,1 

hi 


dorv/?t 


*  i 


Fig   88  —A  Warped  Street  Intersecti-on 

different  from  a  change  at  the  street  intersection,  except  that  the 
former  is  a  little  more  conspicuous.     For  both  appearance  and 


*For  some  formulas  to  assist  in  this  matter,  see  an  article  by  William  B.  Fuller 
in  Journal  of  the  Associated  Engineering  Societies,  Vol.  13,  p.  658-60  or  a  duplicate 
of  the  same  in  Engineering  Record,  Vol  22,  p.  216.  For  an  interesting  and  instruc- 
tive account  of  the  method  of  adjusting  the  grades  at  a  number  of  complicated 
intersections,  see  an  article  by  F.  A.  Calkins  in  Engineering  News,  Vol.  17,  p.  134- 
35,  and  150-51. 


STREET    GRADES. 


32/ 


the  comfort  of  the  traffic,  wherever  there  is  considerable  change 
of  grade  the  two  grade  lines  should  be  connected  by  a  vertical 
curve;  and  if  this  is  properly  done,  a  break  of  grade  in  the  block 
or  elsewhere  is  unobjectionable.  A  vertical  curve  should  be  in- 
serted at  a  change  of  grade  either  of  the  pavement  or  of  the  curb. 

By  breaking  grade  in  the  block,  it  is  possible  to  fit  the  grade 
line  more  closely  to  the  natural  surface,  and  thereby  to  decrease 
the  cost  of  construction,  to  lessen  the  damage  to  abutting  prop- 
erty, and  to  improve  the  general  appearance  of  the  street. 

486.  A  parabola  is  the  best  form  for  a  vertical  curve  and  is 
most  easily  put  in.     In  Fig.  89,  A  B  and  A  C  represent  two  grade 


Fig.  89. — Vertical,  Curve 

lines  meeting  in  the  apex  A,  joined  by  the  vertical  parabola  B  C, 
which  is  tangent  to  the  straight  grade  line  at  B  and  C.  The  curve 
may  be  located  by  measuring  ordinates  vertically  below  the  points 
1,  2,  3,  etc.  The  tangent  distances  A  B  and  A  C  are  equal.  D  E 
is  equal  to  the  rise  in  half  the  length  of  the  curve,  i.  e.,  from  B  to 
A  ;  and  E  C  is  equal  to  the  fall  in  the  second  half,  i.  e.,  from  A  to  C. 
If  n  represents  the  number  of  equidistant  points  to  be  established 
on  the  curve  (including  the  second  tangent  point,  C),  then  the 

T)  TP  _J_    TP  C 

ordinate  at  the  first  point 


x  = 


The   ordinate  at 


any  other  point  is  equal  to  x  times  the  square  of  the  number  of 
equal  divisions  between  B  and  that  point;  that  is,  the  ordinate 
from  2  is  4:r,  from  3  is  9x,  from  4  is  16x,  from  5  is  25x,  and  from 
6  is  36:r.  In  actual  work,  the  grade  elevation  of  the  points  1,  2,  3, 
etc.,  are  to  be  worked  out  in  the  usual  manner;  from  these  eleva- 
tions subtract  the  ordinates  as  computed  above,  and  the  remainder 
is  the  grade  elevation  of  the  respective  points  on  the  parabola  B  C. 


328  STREET   DESIGN.  [CHAP.   IX. 

The  agreement  of  the  elevation  of  the  last  point  on  the  curve,  6  in 
Fig.  89,  with  the  point  C  on  the  tangent,  checks  the  work  of  com- 
puting the  elevations. 

If  the  second  tangent,  A  C,  is  level,  E  C  in  the  above  value 
for  x  is  0;  and  if  the  second  tangent  has  an  up  grade,  E  C  is  minus, 
and  the  numerator  =  D  E  —  EC.  If  the  first  tangent  is  level,  D  E 
—  0;  and  if  the  first  tangent  has  a  down  grade,  D  E  is  minus,  and 
the  numerator  =  E  C-D  E.  The  principles  deduced  for  Fig.  89 
are  equally  true,  if  that  diagram  be  turned  upside  down. 

To  secure  the  best  results,  there  should  be  15  feet  of  curve  for 
each  per  cent  of  change  of  grade,  although  10  feet  for  each  per 
cent  will  give  fair  results.  Long  vertical  curves  make  a  graceful 
street.  The  effect  of  any  proposed  curve  in  lowering  (or  raising) 
the  apex  can  be  judged  of  beforehand  by  remembering  that  the 
distance  from  the  apex  A,  Fig.  89,  to  the  curve  is  equal  to  half  of 
the  difference  in  elevation  between  A  and  the  mean  of  the  eleva- 
tions of  B  and  C. 

487.  CROWN  OF  PAVEMENT.  The  only  reason  for  crowning  a 
pavement,  i.  e.,  for  making  the  center  higher  than  the  sides,  is  to 
afford  surface  drainage;  and  therefore  the  proper  crown  to  be 
given  to  pavements  will  be  considered  under  the  head  of  Street 
Drainage — see  §  509-14,  Chapter  X. 

To  make  intelligible  the  discussion  of  the  succeeding  section, 
it  is  necessary  to  state  here  that  in  general  the  surface  of  the  pave- 
ment consists  either  of  two  planes  meeting  at  or  near  the  center,  or 
of  a  flat  convex  curve,  usually  the  latter;  and  for  present  purposes 
it  is  sufficient  to  say  that  the  average  transverse  slope  is  usually 
between  1  and  3  per  cent  (see  §  513).  The  smoother  the  pavement 
and  the  better  the  construction,  the  less  should  be  the  crown. 

488.  Cross  Section  of  Side-hill  Streets.  The  arrange- 
ment of  the  cross  section  of  a  street  upon  a  side  hill  is  a  matter  re- 
quiring good  judgment,  that  needless  damage  may  not  be  done  to 
the  abutting  property  or  that  the  general  appearance  of  the  street 
may  not  be  uselessly  sacrificed.  In  solving  this  problem  no  fixed 
rules  can  be  laid  down;  but  each  case  must  be  treated  by  itself, 
taking  into  account  the  local  conditions.  Fig.  90  shows  the  nor- 
mal arrangement  for  a  residence  street  on  level  ground;  both 
footways  are  at  the  same  elevation,  the  slope  of  the  parking  is  the 


CROSS    SECTION    OF    SIDE-HILL    STREETS.  329 

same  on  the  two  sides,  the  tops  of  the  curbs  are  at  the  same  level, 
the  gutters  are  of  the  same  depth,  and  the  surface  of  the  street 
rises  equally  from  each  side  to  the  center.  The  normal  section  for 
a  business  street  would  be  the  same  except  that  the  sidewalk 

>Vffi*-6ft—t+  —10 ft-  ->H 30ft ■***-  -  /Oft-  -*K  6ft^*2ff\< 


Fig.  90. — Cross  Section  of  Street  on  Level  Ground. 

would  occupy  all  the  space  between  the  curb  and  the  building 
line.  On  a  side-hill  street  the  above  conditions  can  not  always 
be  realized;  and  various  expedients  must  be  resorted  to,  depending 
upon  the  difference  in  elevation  of  the  two  sides  of  the  street.  The 
following  are  some  of  the  common  expedients. 

1.  If  the  difference  is  not  very  great,  the  curbs  may  be  set 
at  the  same  level,  and  one  sidewalk  may  be  placed  higher  than 
the  other,  the  grade  of  the  parking  being  different  on  the  two 
sides.  On  a  business  street,  where  there  is  no  parking,  the  slope 
of  the  footway  may  be  different  on  the  two  sides.  With  sidewalks 
consisting  of  stone  slabs,  cement,  or  asphalt,  a  slope  of  at  least  \ 
of  an  inch  per  foot  (1  in  96)  is  required  for  drainage,  and  a  slope 
of  more  than  J  of  an  inch  per  foot  (1  in  32)  is  dangerous  when 
covered  with  ice  or  snow. 

2.  A  slight  difference  of  level  may  be  overcome  by  raising  the 
curb,  i.  e.,  by  increasing  the  depth  of  the  gutter,  on  the  high  side, 
and  lowering  the  curb  on  the  low  side,  the  crown  of  the  pave- 
ment remaining  symmetrical  about  the  longitudinal  center  line. 
Fig.  91  shows  an  actual  section  of  a  street  arranged  on  this  plan.* 

Wa/M    \  Roadway  4        Hto/k 


Fig.  91. — Cross  Section  of  Side- hill  Street. 

Except  under  extreme  conditions,  the  curb  should  not  show  more 
than  10  inches  because  of  the  difficulty    of  stepping  to  or  from 

*  Trans.  Amer.  Soc.  of  Civil  Engineers,  Vol.  42,  p  5. 


330  STREET    DESIGN.  [CHAP.   IX. 

the  pavement,  nor  less  than  three  inches  because  of  the  danger  of 
its  being  overflowed  when  the  gutter  is  full  of  melting  snow. 

Sometimes  a  double  curb  is  employed  with  a  horizontal  tread 
about  1  foot  wide  between  the  two  risers.  The  combined  con- 
crete curb  and  gutter  (§  522)  lends  itself  most  readily  to  this  form 
of  construction.    Fig.  92  shows  such  an  arrangement.*    The  ob- 


Fig.  92. — Double  Curb  for  Side-hill  Street. 

jections  to  the  double  curb  are:  1,  its  cost;  2,  the  difficulty  of 
keeping  the  step  neat  and  sanitary;  and  3,  it  lessens  the  width 
available  for  roadway  and  sidewalk.  In  practice  these  objec- 
tions have  not  proved  to  be  serious.  Instead  of  the  double  curb, 
it  has  been  proposed  to  place  the  second  step  at  the  area  line  or 
property  line,  to  which  arrangement  the  owner  is  liable  to  ob- 
ject, particularly  on  a  business  street. 

3.  A  slight  difference  may  also  be  overcome  by  making  the 
upper  side  of  the  pavement  nearly  level  and  giving  the  lower  half 
the  normal  slope. 

4.  The  crown  may  be  moved  toward  the  high  side  of  the  street, 
the  profile  for  each  side  being  determined  in  the  usual  way;  that  is, 
the  surface  of  the  pavement  may  be  two  planes  meeting  at  the 
crown  with  the  intersection  rounded  off  a  little,  or  it  may  be  two 
arcs  of  a  circle  or  a  parabola  tangent  to  a  horizontal  line  at  the 
high  point  (see  §  310  and  §  512).     Fig.  93  is  an  actual  example 


Fig.  93. — Cross  Section  of  Street  on  a  Side  Hill. 

of  this  method  of  solution.*  If  the  longitudinal  grade  is  consid- 
erable, as  it  usually  is  under  such  circumstances,  there  is  no  objec- 
tion to  the  upper  side  of  the  street's  being  exactly  level  transversely. 
The  extreme  of  this  solution  is  to  make  the  surface  of  the  pave- 

*  Trans.  Amer.  Soc,  of  Civil  Engineers,  Vol.  42,  p.  5. 


CROSS   SECTION    OF   SIDE-HILL   STREETS. 


331 


ment  a  right  line  from  the  upper  to  the  lower  side — see  Fig.  94. 
This  arrangement  has  been  objected  to  on  account  of  its  throw- 


Fig.  94. — Cross  Section  of  Street  on  a  Side  Hill. 

ing  all  of  the  drainage  to  one  side  of  the  street;  but  this  is  not  a 
serious  objection,  particularly  if  there  is  a  considerable  longitudi- 
nal grade,  as  there  is  usually. 

5.  Where  there  is  a  considerable  difference  of  elevation  on  a 
residence  street,  it  is  sometimes  wise  to  place  the  footway  next 
to  the  curb,  and  to  allow  the  slope  of  the  parking  to  unite  with 
that  of  the  property — see  Fig.  95. 


Fig.  95. — Cmoss  Section  of  Side-hill  Street. 

6.  When  any  or  all  of  the  above  solutions  fail,  it  may  be  neces- 
sary to  terrace  the  street  and  to  construct  an  upper  and  a  lower 
roadway  as  shown  in  Fig.  96. 


Fig.  96. — Cross  Section  of  Side-hill  Street. 

489.  When  the  street  contains  one  or  more  street-car  tracks, 
the  problem  of  arranging  a  cross  section  on  the  side  of  a  hill  is  still 
more  complicated.  It  is  necessary  that  the  two  sides  of  a  track 
shall  be  at  least  nearly  on  the  same  level;  but  it  is  not  necessary 
that  the  two  tracks  shall  be  at  the  same  elevation.  A  difference 
in  elevation  of  f  of  an  inch  between  rails  of  the  same  track  and  of 
3  inches  between  adjoining  tracks  is  permissible. 

490.  Plans  and  Specifications.  When  a  pavement  is  to 
be  constructed  by  contract,  as  is  almost  the  universal  practice  in 


332  STREET   DESIGN.  [CHAP.  IX. 

this  country,  the  engineer  prepares  plans  and  specifications  which 
constitute  a  detailed  description  of  the  manner  in  which  the  work 
is  to  be  done. 

The  plans  should  consist  of  any  drawings  necessary  to  make 
clear  the  method  of  doing  the  work.  Usually  no  drawings  are 
submitted  except  a  profile,  and  sometimes  also  a  cross  section 
of  the  proposed  pavement.  Occasionally  drawings  are  given 
showing  the  method  of  setting  the  curb,  laying  the  gutter,  placing 
the  inlets,  and  paving  around  manholes,  against  street-car  rails, 
at  street  intersections,  etc.  The  city  engineer  stakes  out  the 
work,  and  hence  no  drawings  are  required  to  show  the  boundaries 
of  the  proposed  improvement. 

The  specifications  should  consist  of  two  distinct  parts:  (1)  full 
particulars  as  to  the  business  portion  of  the  contract  and  the  rela- 
tion of  the  several  parties,  and  (2)  a  technical  description  of  the 
materials  to  be  used  and  the  methods  to  be  employed.  The  first 
are  substantially  the  same  for  all  forms  of  pavements,  while  the 
second  vary  with  the  materials  used.  For  a  full  and  complete  pres- 
entation of  the  business  part  of  pavement  specifications,  see  John- 
son's Engineering  Contracts  and  Specifications;*  the  technical 
parts  will  be  referred  to  in  the  respective  chapters  following. 

491.  STREET  TREES.  It  is  always  desirable  both  for  the  shade 
and  for  the  appearance,  and  usually  possible,  to  have  the  streets, 
at  least  those  devoted  to  residences,  lined  with  trees  on  each  side. 
Although  trees  in  the  streets  have  an  important  sanitary  and 
aesthetic  value,  opinions  differ  regarding  the  proper  responsibility 
for  them.  One  view  vests  all  right  and  title  to  the  tree  in  the 
owner  of  the  property  before  which  it  stands ;  and  the  other  asserts 
that  the  trees  belong  to  the  city  at  large  and  that  the  individual 
has  no  more  right  to  the  tree  in  front  of  his  property  than  has  any 
other  citizen.  In  the  first  case,  the  planting  of  the  tree,  its  kind, 
position,  and  care  depend  upon  the  public  spirit  of  the  property 
holder;  and  as  a  result  the  street  presents  a  motley,  straggling 
appearance  often  with  no  trees  where  they  are  most  needed  for  the 

♦Engineering  Contracts  and  Specifications,  by  J.  B.  Johnson,  Engineering  News 
Publishing  Co.,  New  York  City,  1895.  417  pp.  6  x  9".  $3.50.  This  volume  contains 
a  brief  but  excellent  synopsis  of  the  law  of  contracts  with  illustrative  examples  of 
the  general  and  technical  clauses  of  various  engineering  specifications. 


STREET   TREES.  333 


best  general  effect.  Without  some  degree  of  public  control,  it  is 
impossible  even  to  approximate  the  best  results  of  tree  planting; 
but  fortunately  the  number  of  cities  is  rapidly  increasing  in  which 
the  street  trees  are  under  the  control  of  the  municipal  authorities. 

In  planning  a  system  of  streets,  the  location  of  the  trees  should 
be  definitely  provided  for.  They  should  be  located  in  the  grass 
plats  between  the  sidewalk  and  the  edge  of  the  pavement,  and 
at  a  sufficient  distance  from  both  the  sidewalk  and  the  pavement 
that  there  will  be  no  danger  of  the  roots  lifting  either.  The  trees 
should  be  spaced  in  the  row  so  as  to  permit  each  when  fully  grown 
to  spread  to  its  natural  dimensions,  which  usually  requires  a  space 
of  25  to  40  feet.  Not  infrequently  trees  are  planted  much  too 
close — particularly  in  the  fertile  and  originally  treeless  prairies  of 
the  Mississippi  Valley; — and  are  left  to  crowd  each  other  and  to 
prevent  a  symmetrical  growth.  In  planting  trees,  it  is  well  to 
alternate  those  of  rapid  growth  with  those  which  mature  more 
slowly;  and  then  as  the  latter  increase  in  size  and  demand  more 
room,  the  former,  having  served  their  temporary  purpose,  can  be 
removed.  Increased  stateliness,  impressiveness,  and  charm  is 
secured  if  the  trees,  at  least  the  permanent  ones,  on  any  one  thor- 
oughfare are  of  one  variety.  Different  streets  can  have  different 
kinds  of  trees,  since  in  nearly  all  cities  there  are  a  large  number  of 
suitable  varieties  available. 

492.  In  most  states  there  are  one  or  more  cities  that  have 
obtained — either  officially  or  by  volunteer  civic-improvement 
societies — valuable  experience  as  to  the  varieties  best  suited  to  the 
environment,  from  whom  data  can  doubtless  be  obtained  by  those 
desiring  information  concerning  the  kind  of  trees  to  plant  in  the 
streets  of  any  particular  city. 

493.  The  following  are  the  requirements  for  a  street  tree 
adopted  by  a  commission  of  experts  for  Washington  City.*  "1. 
A  somewhat  compact  stateliness  and  symmetry  of  growth,  as 
distinguished  from  a  low  spreading  or  pendant  form,  so  that  the 
stem  may  reach  a  sufficient  height  to  allow  free  circulation  of  air 
below  the  branches.  2.  An  ample  supply  of  expansive  foliage  of 
bright  early  spring  verdure,  and  rich  in  the  variety  of  colors  and 

*  Proc.  Amer.  Soc.  Municipal  Improvements,  Vol.  5,  p.  97. 


334  STREET   DESIGN.  [CHAP.  IX. 

tints  assumed  during  autumn.  3.  Healthiness,  so  far  as  being 
exempt  from  constitutional  diseases,  as  well  as  by  maladies  fre- 
quently engendered  by  peculiarities  of  soil  and  atmosphere  im- 
purities. 4.  Cleanliness,  characterized  by  a  persistency  of  foliage 
during  the  summer,  freedom  from  fading  flowers,  and  exemption 
from  the  attacks  of  noxious  insects.  5.  It  should  be  easily  trans- 
planted, of  moderately  vigorous  growth,  and  not  inclined  to  throw 
up  shoots  from  the  root  or  lower  portion  of  the  stem.  A  tree  cf 
extremely  rapid  growth  is  generally  short-lived.  6.  The  branches 
should  be  elastic  rather  than  brittle,  that  they  may  withstand 
heavy  storms;  and  lastly,  there  should  be  no  offensive  odor  from 
foliage  or  flowers." 

Of  course,  no  tree  planted  amid  the  artificial  conditions  found 
in  a  large  city  will  fully  meet  such  rigid  requirements.  In  1872, 
at  the  commencement  of  systematic  tree  planting,  the  above  com- 
mission recommended  the  following  list  of  trees.  The  Silver  Maple 
(Acer  dasycarpum),  the  American  Linden  (Tilia  americana),  the 
European  Sycamore  Maple  (Acer  pseudo-platanus)  and  the  Amer- 
ican Elm  (Ulmus  americana)  are  thought  to  fill  all  the  above 
requirements  when  not  subjected  to  the  attacks  of  insects.  The 
Tulip  Tree  (Liriodendron  tulipifera),  Sugar  Maple  (Acer  saccha- 
rinum),  Sweet  Gum  (Liquidamber  styraciflua),  and  the  Red  Maple 
(Acer  rubrum)  are  the  most  beautiful  of  trees,  their  only  drawback 
being  that  of  not  growing  freely  after  transplanting.  The  Nor- 
way Maple  (Acer  platanoides),  the  Negundo  (Acer  negundo), 
and  the  American  Ash  (Fraximus  americana)  are  recommended 
for  certain  places.  The  Button-woods  or  Planes  (Platanus  occi- 
dentalis  and  Platanus  orientalis)  are  rapid  growing,  and  for  wide 
avenues  are  effective  trees. 

As  a  result  of  twenty-five  years'  experience,  the  trees  are  ranked 
as  follows :  *  "  Silver  Maple,  Norway  Maple,  and  Eastern  Plane  side 
by  side  in  the  first  rank;  then  the  Ginkgo,  and  Western  Plane; 
and  last  American  linden,  Oak,  and  Sugar  Maple." 

*  Proc  Amer.  Soc.  Municipal  Improvements,  Vol.  5,  p.  98. 


CHAPTER  X. 
STREET  DRAINAGE, 

495.  The  thorough  drainage  of  a  street  involves  four  elements: 
(1)  the  surface  drainage,  (2)  the  gutters,  (3)  the  catch  basins,  and 
(4)  the  underdrainage.     They  will  be  considered  in  the  reverse  order. 

406.  SUBDRAINAGE.  The  underdrainage  of  a  street  is  the 
first  step  toward  paving  it.  Without  thorough  subdrainage  a  pave- 
ment is  likely  to  settle  here  and  there,  forming  unsightly  depres- 
sions on  the  surface,  and  possibly  breaking  through.  The  subsoil 
may  be  drained  by  one  or  more  lines  of  porous  tile  as  described  in 
§  98-109;  but  as  a  rule  the  surface  and  underground  waters  are 
both  collected  in  the  same  drain,  and  therefore  it  is  advisable  to  lay 
a  line  of  tile  at  each  side  of  the  street  or  to  construct  a  larger  con- 
duit under  the  center  of  the  street.  Since  the  pavement  is  prac- 
tically impervious  to  water,  a  third  line  of  tile  under  the  middle 
of  the  pavement  is  unnecessary,  however  wet  and  retentive  the  soil 
originally. 

If  there  is  a  grass  plat  between  the  pavement  and  sidewalk, 
as  is  usual  on  residence  streets,  the  tile  should  be  laid  under  the 
outer  edge  of  the  parking  or  grass  plat;  and  if  there  is  no  parking, 
the  tile  should  be  laid  under  the  gutter.  The  deeper  the  tile  the 
better  the  drainage  and  the  less  the  liability  of  its  becoming  choked 
with  tree  roots.  The  tile  should  not  be  too  small  since  it  is  to  carry 
both  underground  and  surface  water — the  latter  from  a  smooth 
and  impervious  pavement. 

The  formula  for  size  of  tile  for  the  drainage  of  earth  roads 
(§  103)  is  worthless  for  pavements,  since  in  cities  a  large  pro- 
portion of  the  rain  falls  upon  impervious  roofs,  pavements,  side- 
walks, etc.,  and  nearly  all  speedily  reaches  the  storm-water  sewers. 
This  subject  has  been  very  carefully  studied  in  connection  with  the 


336  STREET   DRAINAGE.  [CHAP.   X. 

design  of  sewers,  and  the  reader  is  referred  to  treatises  on  that 
subject,  for  further  information  concerning  the  size  of  drains  or 
storm-water  sewers  required.* 

497.  CATCH  BASINS.  The  catch  basin  is  a  pit  to  receive  the 
drainage  from  the  surface  of  the  street,  in  which  is  deposited  the 
sand  and  other  solid  matter,  and  from  which  the  water  is  discharged 
into  the  sewer  or  storm-water  drain.  A  catch  basin  should  fulfill 
the  following  conditions:  (1)  The  inlet  should  offer  the  least  possi- 
ble obstruction  to  traffic,  should  have  sufficient  capacity  to  pass 
speedily  all  the  water  reaching  it,  and  should  not  easily  be  choked 
by  leaves,  paper,  straw,  etc.  (2)  The  capacity  below  the  outlet 
should  be  sufficient  to  retain  all  sand  and  road  detritus  and  thus 
prevent  it  from  reaching  the  sewer,  and  will  depend  upon  the  area 
drained  and  the  intervals  between  cleanings.  (3)  The  water  level 
should  be  low  enough  to  prevent  freezing.  (4)  The  construction 
should  be  such  that  the  pit  may  be  easily  cleaned  out.  (5)  The 
pipe  connecting  the  basin  with  the  sewer  should  have  sufficient 
capacity,  and  should  be  so  constructed  as  to  be  easily  freed  of  any 
obstruction.  (6)  It  is  desirable  that  the  outlet  should  be  trapped 
so  as  to  prevent  floating  debris  from  reaching  the  sewer.  (7)  If 
the  catch  basin  discharges  into  a  sewer  which  also  carries  house 
sewage,  the  end  of  the  outlet  pipe  should  be  trapped  to  prevent 
the  escape  of  air  from  the  sewer  to  the  street  through  the  catch 
basin. 

498.  The  Construction.  Catch  basins  are  usually  built  of 
brick  masonry,  and  plastered  on  the  inside,  at  least  up  to  the 
water  line.  Fig.  97,  page  337,  the  standard  of  Champaign,  Ill.,f  is 
a  good  form.  The  opening  of  the  inlet  is  protected  by  six  half -inch 
iron  rods.  The  several  parts  of  the  cast-iron  top  are  f  and  \  inch 
thick;  and  the  total  weight  of  the  castings  is  162  pounds.  The 
pit  requires  1,000  brick.  The  total  cost  of  the  catch  basin  when 
laid  in  1  to  2  natural  cement  mortar  is  $17.00  to  $19.00,  including 
castings,  excavation,  and  the  vitrified  elbow. 

Fig.  98,  page  338,  shows  the  standard  catch  basin  of  Prov- 


*  For  example,  see  Folwell's  Sewerage,  p.  M-73.  3rd  edition.    John  Wiley  &  Sons, 
New  York  City,  1900. 

f  By  courtesy  of  W.  H.  Tarrant,  City  Engineer. 


CATCH    BASINS. 


33? 


idence,  R.  I.*    This  form  differs  from  that  shown  in  Fig  97  in  the 
form  of  the  inlet  and  of  the  trap  for  the  outlet.     The  latter  is  made 


i 


( 


36 


/  Cement  Mortar  P/ajter 

sssssssssssssbssssssssm 
Cro55  5ectior? 


r 
1 


Plar?of  Casting 

Fig.  97  —Champaign  Catch  Bastn. 

of  iron  cast  in  a  single  piece,  and  is  somewhat  complicated  in 
form,  but  a  careful  study  of  the  two  views  shown  in  Fig.  98  wall 
make  the  construction  reasonably  clear.  The  seal  in  Fig.  98  is 
better  than  that  in  Fig.  97;  but  the  latter  is  used  only  writh  storm- 
wrater  sewers  and  for  such  use  the  trap  is  sufficient.  Not  infre- 
quently, however  the  outlet  of  the  catch  basin  is  left  untrapped; 
and  sometimes  an  inlet  is  connected  to  a  sewer  without  the  inter- 


*By  courtesy  of  Otis  F.  Clapp,  City  Engineer. 


338 


STREET    DRAINAGE. 


[CHAP.   Xo 


vention  of  either  a  catch  basin  or  a  trap.    This  practice  is  likely 
to  clog  the  sewer. 

! 


Plan  without  Manhole  Frame 
Ftg.  98. — Providence  Catch  Basin. 

Fig.  99,  page  339,  is  the  standard  for  Milwaukee,  Wis.*  This 
diagram  is  presented  to  show  (1)  the  form  of  the  inlet,  (2)  the 
method  of  preventing  floating  debris  from  entering  the  outlet,  and 
(3)  the  method  of  ventilating  the  sewer. 

Fig.  100,  page  339,  shows  the  standard  form  in  St.  Pancras 
Vestry,  London,  England. f 

In  England  many  earthenware  catch  basins  or  "gully  pits"  are 
used.     Some    of   these    forms    are    quite    complicated.     American 


*By  courtesy  of  C.  J.  Poetsch,  City  Engineer. 

t  From  a  special  report  by  William  Nisbet  Blair,  Vestry  Engineer. 


CATCH    BASINS. 


339 


engineers  object  to  earthenware  pits  on  account  of  (1)  their  limited 
size,  (2)  their  great  cost,  and  (3)  their  liability  to  be  broken  by  the 
weight  and  jar  of  the  street  traffic. 


Fig.  99. — Milwaukee  Catch  Basin. 


499.  Location.  The  catch  basin  is  usually  placed  near  the  curb 
with  the  cover  in  the  sidewalk  or  the  parking.  It  is  objectionable 
to  have  the  cover  in  the  sidewalk,  since  (1)  the  cover  itself  is  some- 


Section 


Plan 


Fig.  100. — St.  Pancras  Catch  Basin. 


thing  of  an  obstruction  to  travel  and  is  dangerous  when  it  wears 
smooth  or  is  covered  with  snow,  (2)  the  clearing  of  the  pit  seriously 
interferes  with  the  convenient  use  of  the  footway,  and  (3)  in  empty- 
ing the  pit  the  sludge  is  likely  to  be  spilled  on  the  footway,  and  at 
best  the  odor  is  offensive.  In  some  cities  these  objections  are  elim- 
inated by  placing  the  inlet  at  the  curb  line  and  conducting  the  drain- 
age to  a  catch  basin  near  the  center  of  the  street,  one  basin  serving 
for  two  or  more  inlets.  Notice  that  the  catch  basin  shown  in  Fig. 
100  cleans  out  in  the  gutter. 


340  STREET   DRAINAGE.  [CHAP.   X. 

It  is  customary  to  place  a  catch  basin  at  the  corner  of  the  curb. 
For  additional  objections  to  this  location,  see  §  506. 

The  number  and  capacity  of  catch  basins  will  depend  upon  the 
area  drained,  the  amount  of  rain,  the  grade  of  the  gutter,  etc.  On 
streets  having  light  or  level  longitudinal  grades  catch  basins  may 
be  constructed  at  intervals  along  the  gutter  as  the  circumstances 
require. 

500.  Form  of  Cover.  When  a  catch  basin  or  sewer  manhole 
is  located  in  a  pavement,  the  shape  and  the  surface  of  the  cover 
require  attention.  The  upper  surface  of  the  cover  and  also  of  its 
frame  should  be  covered  with  projections  to  afford  a  good  foothold 
and  to  prevent  it  from  wearing  slippery.  The  best  form  for  the 
frame  depends  upon  the  material  of  the  pavement.  For  macadam 
and  asphalt  the  round  frame  is  best,  since  it  offers  least  obstruction 
to  traffic;  the  next  best  form  is  a  square  frame  set  diagonally  to  the 
line  of  travel.  For  a  pavement  made  of  bricks  or  stone  blocks,  the 
frame  set  with  its  sides  parallel  to  the  length  of  the  street  is  best, 
because  the  bricks  or  blocks  can  be  most  closely  fitted  against  this 
form.  In  Europe  and  in  many  American  cities,  it  is  customary  to 
use  only  a  square  form,  and  to  set  it  diagonally  in  macadam  and 
asphalt  pavements,  and  square  in  stone  block  and  brick. 

Often  water-gate  or  stop-box  covers  are  round  in  plan  and  have 
a  convex  surface,  although  the  convex  surface  is  very  objectionable. 
The  better  form  is  a  cover  round  in  plan  with  a  flat  recessed  top 
set  flush  with  the  pavement.  Preferably  the  portion  below  the 
ground  should  be  provided  with  a  cast  screw  for  adjusting  the 
height.    This  form  may  be  had  of  dealers  in  street-drainage  goods. 

501.  The  Inlet.  In  a  general  way,  there  are  stone  and  cast-iron 
inlets.  The  former  consist  either  of  an  opening  between  a  stone 
cover  and  a  stone  floor,  or  a  slot  through  the  stone  curb  (see  Fig.  98, 
page  338).  This  form  is  usually  entirely  open,  but  it  is  sometimes 
barred  with  one  or  two  horizontal  iron  rods. 

There  are  a  great  variety  of  cast-iron  inlets  on  the  market,  which 
may  be  classified  as  being  straight  or  curved,  and  also  as  having  a 
vertical  or  a  horizontal  opening.  Fig.  101,  page  341,  shows  an  un- 
protected straight  vertical  inlet.  Sometimes  the  opening  is  pro- 
tected by  one  or  more  horizontal  or  vertical  rods.  The  latter  arc 
the  better,  as  they  offer  greater  protection  against  the  entrance  cf 


CATCH    BASINS. 


341 


debris — particularly  sticks  and  boards.  Fig.  102  shows  a  vertical 
front  curved  for  a  corner,  having  vertical  bars.  Fig.  103  and  104 
are  two  styles  of  a  form  having  both  a  vertical  and  a  horizontal 
opening.     Notice  that  Fig.  100,  page  339,  has  only  a  horizontal  open- 


Fig.   101. 


Fig.  102. 


ing.  A  horizontal  opening  is  not  so  good  as  a  vertical  one,  since  the 
former  is  easily  stopped  by  a  few  leaves,  and  the  accumulation  of 
water  makes  the  stoppage  more  complete;  while  the  barred  vertical 
opening  is  less  easily  obstructed,  and  as  the  water  rises  it  can  pour 
over  the  obstruction  already  formed. 


Fig.  103. 


Fig.  104. 


502.  Inlet  without  Catch  Basin.  It  is  sometimes  desirable  to 
connect  two  or  more  inlets  to  one  catch  basin — for  example,  see 
§  507.  There  are  various  forms  of  such  inlets  on  the  market 
and  many  cities  have  their  own  special  designs.  Fig.  '105,-  page 
342,  shows  the  form  of  inlet  used  in  such  a  case  at  Omaha, 
Nebraska.*  The  entrance  A  is  reduced  by  cast  ribs  to  three  open- 
ings 6"  X  9"  at  the  top  and  4}"  X  2"  openings  at  the  bottom. 
The  section  B  is  rectangular  in  plan  at  both  top  and  bottom.  The 
section  C  is  rectangular  at  the  top  and  circular  at  the  bottom,  and 
fits  into  the  hub  of  a  vitrified  elbow.  Fig.  106,  page  342,  shows  a 
commercial  form  of  inlet,  which  has  an  adjustable  curb.  It  is  made 
to  fit  various  sizes  of  outlet  pipe. 


*By  courtesy  of  Andrew  Kosewater,  City  Engineer. 


342 


STREET    DRAINAGE. 


[CHAP.   X. 


503.  GUTTERS.  The  Material.  Ordinarily  the  surface  of  the 
pavement  adjacent  to  the  curb  serves  as  a  channel  to  convey  the 
drainage  to  the  nearest  inlet,  i.  e.,  the  gutter  is  formed  of  the  same 
material  as  the  pavement.  With  an  asphalt  or  macadam  pave- 
ment, it  is  customary  to  lay  brick  or  stone  blocks  in  the  gutters — 
with  asphalt  to  prevent  its  deterioration  from  being  continually 
covered  with  mud  and  water,  and  with  macadam  to  prevent  flow- 
ing water  from  disintegrating  it. 

A  combined  concrete  curb  and  gutter  (§  522)  is  frequently  used, 
particularly  with  asphalt,  brick,  or  macadam  on  residence  streets. 


5/de/ra/H 

■UMtMMWr 


5and 


Fig.  105 — Omaha  Inlet  without 
Catch  Basin. 


Fig.  106. — Commercial  Inlet  without 
Catch  Basin. 


A  concrete  gutter  is  objectionable  on  a  macadamized  street,  on 
account  of  the  crushed  stone's  wearing  below  the  edge  of  the  gutter, 
a  condition  which  interferes  with  the  drainage;  but  if  the  macadam 
surface  is  reasonably  well  cared  for,  this  objection  is  not  serious.  A 
concrete  gutter  has  been  objected  to  for  any  pavement  owing  to 
the  liability  of  a  rut  to  form  along  its  outer  edge.  In  practice  neither 
of  these  objections  has  proved  to  be  serious.  A  concrete  gutter  is 
more  efficient  and  looks  better  than  any  other  material  except 
asphalt. 

Usually  the  gutter  is  formed  by  continuing  the   ordinary  slope 
of  the  pavement  until  it  intersects  the  curb;   but  occasionally  the 


GUTTERS.  343 


outer  edge  of  the  pavement  is  given  an  upward  inclination,  thus  form- 
ing a  flat  V-shaped  channel  a  little  way  from  the  curb.  This  con- 
struction makes  an  excellent  channel  for  the  water,  but  prevents 
the  driving  of  a  carriage  close  enough  to  the  curb  to  allow  people 
to  step  in  or  out  easily. 

In  some  cases  the  curb  is  set  and  the  gutter  formed  before  the 
pavement  is  laid,  in  which  case  the  curb  and  gutter  are  constructed 
as  they  would  have  been  if  the  street  were  to  be  paved, — the  gutter 
being  composed  of  stone  blocks,  brick,  or  concrete  (§  520).  Some- 
times a  street  is  macadamized  or  graveled  when  it  is  not  desired  to 
incur  the  expense  of  setting  a  curb,  in  which  case  the  gutter  is  built 
of  cobble  stones,  or  stone  blocks,  or  brick,  in  the  form  of  a  very  flat 
V  with  the  side  next  the  property  much  the  steeper. 

504.  Depth.  Where  a  curb  is  used,  the  gutter  should  not  be  so 
deep  as  to  present  a  high  step  for  pedestrians,  nor  so  shallow  as  to 
be  in  danger  of  being  overflowed.  Not  infrequently  gutters  are  made 
needlessly  deep.  It  is  easier  to  keep  a  curb  in  line  with  a  shallow  gut- 
ter than  a  deep  one.  On  streets  having  a  considerable  longitudinal 
grade  the  gutter  can  have  a  uniform  depth,  inlets  being  inserted 
to  drawT  off  the  surplus  wrater;  but  on  streets  having  nearly  level 
grades,  the  gutter  must  increase  in  depth  as  the  inlet  is  approached. 
This  can  be  done  with  a  stone  curb,  but  not  with  a  combination  con- 
crete curb  and  gutter  (§  522),  since  the  latter  is  made  in  moulds  and 
hence  must  have  a  uniform  cross  section ;  and  therefore  with  a  con- 
crete curb  and  gutter,  it  may  be  necessary  to  put  a  summit  in  the 
pavement  to  secure  proper  drainage  of  the  gutters.  Except  in 
extreme  cases,  the  gutter  should  not  be  deeper  than  9  inches  nor 
shallower  than  3  inches ;  and  ordinarily  it  should  not  be  more  than 
8  nor  less  than  4  inches — usually  it  is  5  or  6  inches. 

It  may  be  necessary  to  modify  the  preceding  rules  when  one 
side  of  the  street  is  higher  than  the  other  (see  §  488).  In  localities 
where  there  is  a  good  deal  of  snow,  the  gutter  must  be  deeper  than 
stated  above,  for  shallow  gutters  readily  become  clogged  with 
snow  and  slush.  In  some  northern  cities,  the  snow  is  habitually 
allowed  to  pack  upon  the  surface  of  the  street  to  a  depth  of  6  or  more 
inches,  in  which  places  the  depth  of  the  curb  must  be  extremely 
deep  to  prevent  the  melting  snow  and  water  from  filling  the  gutter 
and  flowing  over  the  sidewalk  into  the  basements. 


344  STREET   DRAINAGE.  [CHAP.  X. 

505.  Grade.  For  most  materials  with  which  gutters  are  paved, 
it  is  improbable  that  the  grade  will  be  so  steep  as  to  do  serious  harm. 
Crushed  stone  and  gravel  are  exceptions  to  this  rule,  however,  and 
these  materials  must  not  be  laid  on  too  steep  a  grade.  They  may  be 
used  on  a  2  per  cent  grade  provided  the  volume  of  water  is  not  too 
great. 

The  minimum  grade  permissible  in  the  gutter  will  depend  chiefly 
upon  the  material  with  which  it  is  paved,  but  somewhat  upon  the 
cost  of  catch  basins.  Almost  any  grade  can  be  obtained  by  estab- 
lishing catch  basins  close  together  and  raising  the  gutter  half  wray 
between  them.  In  a  number  of  cities  the  minimum  grade  of  gutters 
paved  with  granite  blocks,  brick,  rectangular  wrood  blocks,  or  mac- 
adam is  1  in  300  or  400  .  Except  under  very  favorable  circumstances, 
a  slope  of  1  in  200,  J  of  1  per  cent,  should  be  regarded  as  the  minimum. 

Asphalt  decays  if  continually  wet,  and  therefore  the  condition 
governing  the  minimum  permissible  grade  is  different  for  that  than 
that  for  other  materials.  With  a  slope  of  less  than  1  per  cent,  the 
gutter  will  not  keep  itself  clean,  consequently  the  asphalt  will  decay 
owing  to  the  action  of  mud  and  water;  and  hence  asphalt  should  not 
be  laid  in  a  gutter  having  a  fall  of  less  than  1  in  100.  If  this  fall  can 
not  be  obtained,  a  concrete  gutter  should  be  used,  or  the  gutter 
should  be  paved  with  vitrified  brick  or  carefully  dressed  granite 
blocks. 

506.  DRAINAGE  AT  STREET  INTERSECTION.  In  most  cities  it 
:.s  customary  to  construct  catch  basins  at  the  corner  of  the  curb? 
using  an  inlet  with  a  curved  face.  This  practice  is  very  objec- 
tionable. 

If  the  walk  across  the  street  is  elevated  above  the  pavement,  it 
is  necessary  either  to  carry  the  water  under  the  walk  in  a  pipe,  or  to 
stop  the  cross  walk  within  a  short  distance  of  the  curb  to  leave  a 
channel  for  the  water.  The  latter  method  is  necessary  where  there 
is  much  water.  Frequently  this  channel  is  left  open  at  the  top,  and 
sometimes  it  is  covered  with  a  cast-iron  plate  with  one  edge  resting 
in  a  rabbet  in  the  curb  and  the  opposite  one  in  a  head  stone  or  false 
curb  set  at  the  end  of  the  cross  walk.  The  covered  gutter  is  much 
better  than  the  open  one,  although  the  cast  plates  are  frequently 
struck  by  wheels  and  broken.  This  solution  of  the  problem  is  fur- 
ther objectionable  since  a  wheel  in  turning  the  corner  must  sur- 


DRAINAGE   AT   STREET   INTERSECTION. 


345 


Cvrb 


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Cotc/?Ba3/r? 


fir 


Jr         forA/hg 


/ 


Wa//r 


'/ 


1 


mount  the  first  raised  cross  walk,  then  descend  to  the  bottom  of  the 
gutter,  and  finally  climb  over  the  second  cross  walk.  The  face  of 
the  inlet  usually  has  a  depth  of  8  to  12  inches  below  the  top 
of  the  curb;  and  hence  if  the  sidewalks  are  wide  or  the  parking  is 
narrow,  the  shock  to  a  vehicle  going  around  such  a  corner  is  con- 
siderable. 

If  the  cross  walk  is  not  elevated,  the  step  from  the  curb  to  the 
bottom  of  the  gutter  is  uncomfortably  high,  and  besides  pedestrians 
are  compelled  to  cross  the  gutter  where  there  is  the  most  water. 

507.  A  much  better  arrangement  than  either  of  the  above  is 
to  place  an  inlet  at  each  side  of  the  corner.  Each  inlet  may  have 
its  own  catch  basin,  or  the  two  may  connect  with  a  single  pit  by 
means  of  tile  or  vitrified  pipe  underground.  Fig.  107  shows  such 
an  arrangement.  Instead  of  this 
plan,  the  two  inlets  at  each  of  the 
four  corners  of  the  street  intersec- 
tion may  be  connected  with  a 
single  catch  basin  placed  in  the 
middle  of  the  intersection  or  in 
other  suitable  location.  The  inlet 
not  connected  directly  with  a  catch 
basin  can  be  made  by  inserting  the 
hub  of  a  curved  vitrified  pipe  in  the 
bottom  of  a  cast  inlet  box  (see 
Fig.  105  and  106,  page  342). 

The  advantage  of  the  method  shown  in  Fig.  107  is  that  it  allows 
the  intersection  to  be  paved  almost  level  with  the  top  of  the  curb, 
and  hence  there  is  no  obstruction  to  either  pedestrian  or  vehicular 
traffic.  The  only  objection  to  it  is  the  expense  for  either  the  extra 
catch  basin  or  the  extra  inlet  and  the  connecting  pipe,  but  the  advan- 
tage is  well  worth  this  comparatively  small  expense. 

508.  Where  there  are  no  storm-water  sewers,  the  gutter  is 
sometimes  carried  across  the  street  intersection.  This  is  objection- 
able at  any  season,  and  particularly  so  when  the  gutter  is  filled  with 
snow  or  ice.  If  the  gutter  is  deep  or  the  grade  is  steep,  the  water 
may  be  carried  under  the  intersection  by  a  shallow  culvert  with 
cast-iron  top,  or  better  in  a  cast-iron  pipe;  but  if  the  gutter  is  shal- 
low or  the  grade  nearly  level,  the  road  surface  should  be  raised  a 


Fig.  107. — Inlets  at  Street  Corner. 


346  STREET   DRAINAGE.  [CHAP.   X. 

little  to  give  room  for  a  cast-iron  storm-water  drain  under  the  road- 
way. The  elevated  intersection  may  be  a  slight  obstruction  to 
travel,  but  it  is  preferable  to  two  open  gutters. 

509.  SURFACE  DRAINAGE.  The  drainage  of  the  surface  of  the 
pavement  is  provided  for  by  making  the  center  of  the  pavement 
higher  than  the  sides.  The  principle  governing  the  amount  of  crown 
for  pavements  is  somewhat  different  from  that  of  earth,  gravel,  or 
macadam  roads.  First,  a  hard,  smooth  and  practically  impervi- 
ous pavement  needs  no  crown  for  the  drainage  of  the  surface;  and 
on  such  a  pavement,  the  only  advantage  of  a  transverse  slope  is  to 
drain  shallow  depressions  due  to  faulty  construction,  wear,  or  a  set- 
tlement of  the  foundation,  and  to  aid  the  rains  in  washing  the  pave- 
ments. Second,  the  surface  of  the  pavement  has  no  tendency  to 
wash;  and  hence  the  crown  need  not  be  increased  on  a  grade  as  in 
the  case  of  earth  roads.  The  less  the  crown  the  better  for  the  traffic, 
and  the  more  uniformly  will  the  travel  be  distributed  over  the  pave- 
ment, although  a  slight  crown  is  inappreciable  in  either  of  these 
respects.  Therefore  pavements  require  only  crown  enough  to  drain 
depressions  of  the  surface  due  to  faulty  construction,  to  wear,  or 
to  settlement  of  the  foundation;  and  the  crown  may  decrease  as 
the  grade  increases. 

510.  Crown.  There  has  been  much  discussion  as  to  the  best  form 
of  the  surface  of  a  pavement.  Some  claim  that  it  should  be  a  con- 
tinuous curve, while  others  contend  that  it  should  consist  of  two  planes 
meeting  in  the  center.  The  curved  profile  is  defective  in  that  it  gives 
too  little  inclination  near  the  middle,  the  result  being  that  the  pave- 
ment wears  hollow  in  the  center  and  permits  water  to  stand  there. 
To  overcome  this  objection  some  engineers  raise  the  center  of  the 
pavement  J  or  f  of  an  inch  above  the  curved  cross  section.  The 
objection  to  the  two  planes  is  that  the  sides  wear  hollow  and  hold 
water.  An  advantage  of  the  curved  profile  is  that  the  center  of  the 
street,  which  is  the  part  especially  devoted  to  travel,  is  nearly  flat; 
while  the  sides,  which  have  the  greater  inclination,  are  occupied  by 
teams  standing  at  the  curb.  Another  advantage  of  the  curved 
profile  is  that  it  gives  a  deeper  gutter,  which  confines  the  storm 
water  to  a  smaller  portion  of  the  street  and  reduces  the  interfer- 
ence with  pedestrian  traffic. 

It  is  sometimes  claimed  that  the  curved  form  will  support  the 


SURFACE   DRAINAGE.  347 


greater  load,  because  of  its  arch  action;  but  the  arch  action  of  a 
pavement  is  entirely  inappreciable,  owing  to  the  flatness  of  the  arch, 
to  the  imperfect  fit  of  the  so-called  arch  stones,  and  to  the  insta- 
bility of  the  abutments  or  curbs. 

The  surface  is  usually  a  continuous  curve — generally  a  parabola. 
For  the  methods  of  staking  out  each,  see  §  310  and  §  312,  pages 
200  and  201. 

511.  The  early  pavements  in  this  country  and  at  present  those 
in  some  cities  in  Europe  and  South  America,  slope  from  both  sides 
towards  the  center.  In  this  form  the  most  valuable  part  of  the 
street  is  devoted  to  drainage  purposes,  and  it  is  difficult  to  carry 
the  water  to  an  intersecting  street.  The  pavements  of  alleys  usu- 
ally slope  to  the  center.  This  form  is  better  for  alleys  than  a  gutter 
at  each  side,  since  it  keeps  the  storm  water  from  flowing  along  the 
side  of  buildings  and  possibly  interfering  with  light  areas,  cellar 
stairways,  etc.,  and  it  also  carries  the  water  over  the  sidewalk  with 
less  annoyance  to  pedestrian  traffic. 

512.  When  construction  begins,  it  is  wise  to  give  the  one  in 
charge  of  the  work  a  drawing  somewhat   like  Fig.  108,  showing 


o 

4 

a. 

it    . 

•« 

a 

• 

* 

o 

I 

,T 

._T 

T 

1 

1 

,1 

1 

.T 
I 

J 

J 

5vb-grad» 

Fig.  108. — Method  of  Showing  Crown  of  Pavement. 

the  relation  between  the  top  of  the  curbs  and  the  grade  of  the 
foundation,  the  top  of  the  concrete,  and  the  top  of  the  finished 
pavement.  Such  a  drawing  prevents  misunderstandings  and  dis- 
putes. Notice  that  the  curves  in  Fig.  108  are  not  exact  parabolas, 
the  ordinates  at  4  and  12  being  J  inch  too  long;  but  this  is  suffi- 
ciently exact,  since  it  is  not  possible  to  secure  mathematical  pre- 
cision in  this  class  of  work. 


348  STREET   DRAINAGE.  [CHAP.  X. 

513.  Crown  in  Various  Cities.  The  following  is  the  practice  in 
different  cities.  All  use  the  curved  profile,  and  it  is  immaterial 
whether  it  be  called  a  circular  or  a  parabolic  arc. 

Boston.  In  Boston*  the  crown  per  foot  of  half  width  of  the 
pavement  is  as  follows:  macadam,  -|  inch;  granite  block,  -f  inch; 
sheet  asphalt,  asphalt  block,  or  brick,  T5^  inch.  On  side-hill  streets 
the  maximum  difference  in  elevation  between  the  crown  and  the 
pavement  next  to  the  curb  is  as  follows:  for  macadam,  J  inch  per 
foot  of  the  half  width  of  the  pavement;  for  granite  block,  }  inch 
per  foot;  and  for  sheet  asphalt,  asphalt  block,  or  brick,  -^  inch. 
If  there  are  one  or  more  street-car  tracks  on  the  street,  the  above 
crown  is  obtained  at  the  rail  nearest  the  curb. 

New  York.  In  New  York  city  |  the  crown  for  asphalt  streets 
is  T-J^  of  the  distance  between  curbs,  or  say  J  inch  per  foot  of  the 
half  width ;  %  and  for  brick  or  granite  is  -fT  of  the  half  width  or  £  inch 
per  foot. 

Chicago.  In  Chicago  §  the  standard  crown  for  asphalt,  brick, 
or  granite  block,  is  a  minimum  of  2  per  cent  and  a  maximum  of  5 
per  cent  of  the  half  width;  for  macadam,  a  minimum  of  4  per  cent 
and  a  maximum  of  8  per  cent. 

Omaha.  In  Omaha  the  crown  is  decreased  as  the  steepness  of 
the  grade  increases,  a  method  which  is  commendable.  The  crown 
for  asphalt  is:  |  C=w  (100— 4p)-^  5,000,  in  which  C  =  the  crown 
of  the  pavement  in  feet,  w  =  the  distance  between  the  curbs  in  feet, 
and  p  =  the  per  cent  of  the  longitudinal  grade.  For  brick,  stone 
block,  or  wood  block,  the  crown  is  five  sixths  of  that  for  asphalt. 
A  formula  for  crown  formerly  used  in  Omaha  gave  a  less  crown 
than  the  above  rule  for  brick,  stone  block,  and  wood  block,  and 
as  much  less  crown  for  asphalt.     The  former  formula  is : 

for  brick,  stone  block,  and  wood  block,  C  =  w  (20  —  p)-~  1,600 
for  sheet  asphalt  C  =  w  (9  -  p)  -5-  600. 

Notice  that  in  the  cities  mentioned  above  asphalt  has  the 
smallest  crown  of  any  form  of  pavement,  except  in  Omaha,  where 

*By  authority  of  William  Jackson,  City  Engineer. 

t  By  authority  of  E.  P.  North,  Water  Purveyor,  in  charge  of  pavements. 
%  This  is  the  same  crown  as  that  used  on  the  celebrated  Alexander  Bridge  in 
Paris,  France,  built  in  1899. 

§By  authority  of  J.  B.  Hittle,  Chief  Engineer  of  Streets. 
|!  By  authority  of  Andrew  Rosewater,  City  Engineer. 


crown.  349 


it  has  the  largest.  Considering  only  the  smoothness  of  the  surface, 
it  appears  that  asphalt  should  have  the  least  crown;  but  consid- 
ering only  the  fact  that  asphalt  rots  when  continually  wet,  it  appears 
that  asphalt  should  have  a  large  crown. 

514.  The  above  rules  for  crown  must  be  modified  somewhat 
when  the  two  sides  of  the  street  are  not  at  the  same  elevation — 
see  §  488,  page  328. 


CHAPTER  XI. 
CURBS   AND   GUTTERS. 

516.  CURB.  A  curb  is  a  plank  or  slab  of  stone  set  at  the  edge 
of  the  roadway  to  protect  the  sidewalk  or  tree  space  and  to  form 
the  side  of  the  gutter.  Curbs  are  not  usually  set  except  where  the 
street  is  paved,  but  they  greatly  improve  the  appearance  of  an 
unpaved  street  and  protect  the  grass  plats  at  the  side  of  the  street, 
particularly  during  the  muddy  season. 

Curbs  are  usually  formed  of  natural  stone,  although  concrete 
curb,  usually  combined  concrete  curb  and  gutter,  are  increasing  very 
rapidly  in  recent  years — partly  because  of  the  decrease  in  the  price 
of  Portland  cement.  Granite  is  the  best  natural  stone,  but  Or  is 
usually  very  expensive.  Limestone  and  sandstone  are  frequently 
used,  but  they  are  generally  too  easily  chipped  or  broken.  Con- 
crete, unless  made  with  unusual  care  or  protected  by  steel  on  the 
edge,  is  too  friable  for  a  business  street  where  heavy  loads  fre- 
quently back  up  against  the  curb. 

517.  Stone  Curb.  Granite  curb  are  obtained  in  large  quan- 
tities in  the  localities  mentioned  in  §  813.  Hudson  River  blue- 
stone,  a  variety  of  sandstone  commercially  known  as  bluestone, 
is  much  used  for  curbs,  on  account  of  its  hardness,  durability,  and 
great  transverse  strength.  It  is  evenly  bedded,  and  splits  with  a 
smooth  surface,  and  is  found  in  large  quantities  in  the  counties  of 
the  state  of  New  York  adjoining  the  Hudson  River  from  Albany 
to  New  York  city.  A  sandstone  much  used  for  curbs  is  quarried 
in  great  quantities  at  Berea,  Ohio,  near  Cleveland.  It  is  generally 
a  uniform  gray,  but  is  sometimes  spotted  with  iron  stains.  It  is 
easily  quarried,  but  is  too  soft  and  friable  for  curbs  except  on 
residence  streets.  Sandstone  curbs  are  also  obtained  in  consider- 
able quantities  in  the  localities  mentioned  in  §  815-20. 

350 


CURB.  351 


518.  The  thickness  should  be  sufficient  to  give  strength  to 
resist  the  blows  of  wheels  and  to  prevent  the  frost  in  the  earth 
back  of  the  curb  from  breaking  it  off  at  the  top  of  the  gutter. 
They  are  4  to  8  inches  thick,  usually  4  to  6  inches,  depending  upon 
the  quality  of  the  stone  and  the  locality.  The  depth  must  be 
sufficient  to  prevent  the  thrust  of  the  earth  behind  the  curb  from 
overturning  it,  and  is  usually  18  to  24  inches.  If  the  sections  are 
too  short,  it  is  difficult  to  keep  them  in  place  and  the  general 
appearance  is  not  good;  and  if  they  are  too  long,  it  is  difficult  to 
handle  and  set  them,  and  nearly  impossible  to  get  a  firm  bearing  on 
the  bottom.     They  usually  vary  from  3  to  8  feet. 

The  exposed  face  of  the  curb  should  be  bush-hammered  or 
axed;  and  where  the  sidewalk  extends  to  the  curb,  the  back  also 
should  be  smoothly  dressed  so  the  sidewalk  may  fit  closely  against 
the  curb.  The  upper  face  should  be  cut  to  a  slight  bevel  with  the 
front  face,  say  %  inch  to  the  foot,  so  that  when  the  face  of  the  curb 
is  set  with  a  little  inclination  backward,  the  top  face  will  be. level 
or  slope  downward  and  to  the  front  a  trifle.  The  pavement  slopes 
toward  the  gutter,  and  therefore  a  wagon  wheel  inclines  toward  the 
curb;  hence  the  curb  is  set  leaning  back  a  little  to  prevent  a  wheel 
from  striking  the  face  when  running  at  the  inner  edge  of  the  gutter 
and  also  to  secure  increased  stability.  The  curb  is  usually  cut 
with  a  square  corner  at  the  outer  upper  edge;  but  it  would  be  better 
if  this  corner  were  rounded  off  slightly,  say  to  a  radius  equal  to  one 
third  of  the  thickness  of  the  curb,  to  decrease  the  tendency  to  chip. 
The  ends  of  the  sections  should  be  smoothly  dressed  to  the  ex- 
posed depth,  and  the  part  not  exposed  should  be  knocked  off  so  as 
to  permit  the  dressed  ends  to  come  into  close  contact.  The  ends 
should  fit  closely  for  appearance  and  to  prevent  the  earth,  partic- 
ularly if  sand,  from  running  from  behind  the  curb  between  the  sec- 
tions into  the  gutter,  or  to  prevent  the  sand  cushion  of  a  brick 
pavement  from  running  from  under  the  bricks  into  these  cracks 
and  possibly  through  them  into  holes  behind  the  curb.  In  a 
number  of  European  cities,  notably  Brussels,  the  curb  is  cut  with 
a  tongue  in  one  piece  which  fits  into  a  groove  in  the  next  piece,  to 
aid  in  keeping  the  curb  to  line. 

The  curb  should  be  set  with  a  uniform  batter,  in  a  straight  line, 
and  on  a  regular  grade.     To  fulfill  these  conditions  requires  careful 


352  CURBS   AND    GUTTERS.  [CHAP.  XI. 

work  in  the  first  place,  and  to  prevent  the  curb  from  subsequently 
getting  displaced  requires  proper  design  and  thorough  workman- 
ship. The  trench  in  which  the  curb  is  to  be  set  should  be  dug  4  to 
6  inches  below  the  base  of  the  curb  .to  allow  for  a  layer  of  gravel  on 
which  to  set  the  stone;  and  the  width  of  the  trench  should  be  at 
least  three  times  the  thickness  of  the  curb  to  allow  room  for  ram- 
ming the  earth  around  the  stone.  The  bottom  of  the  trench  should 
be.  made  smooth  and  be  thoroughly  consolidated  by  ramming,  and 
the  gravel  also  should  be  compacted.  Where  gravel  is  expensive, 
it  is  dispensed  with,  the  curb  being  set  upon  brick  or  stone.  In 
filling  the  trench,  the  earth  should  be  thoroughly  rammed  in  layers 
not  more  than  4  inches  thick.  Where  gravel  is  plentiful,  it  is 
sometimes  specified  that  the  trench  shall  be  filled  with  gravel  to 
8  or  10  inches  from  the  top. 

In  the  past  there  has  been  so  much  trouble  in  keeping  Curbs  in 
line,  that  within  recent  years  there  has  been  a  general  tendency  to 
set  the  curb  in  a  bed  of  concrete — particularly  when  concrete  is 
used  for  the  foundation  of  the  pavement.  A  6-inch  layer  of  con- 
crete is  deposited  in  the  trench  and  the  curb  set  upon  it,  after  which 
the  trench  is  filled  with  concrete  on  the  street  side  up  to  the  base  of 
the  proposed  pavement  and  on  the  back  side  nearly  up  to  the  top  of 
the  curb.  When  set  in  concrete,  the  curb  does  not  need  to  be  as 
deep  as  otherwise,  since  the  concrete  then  practically  becomes  a 
part  of  the  curb. 

519.  Cost.  In  most  localities,  split  sandstone  or  limestone 
curbing  4  to  5  inches  thick  can  be  had  for  20  to  25  cents  per  square 
foot  f.  o.  b.  cars  at  the  destination ;  and  often  sawed  stone  can  be 
had  at  about  the  same  price.  The  additional  cost  of  a  bush-ham- 
mered or  axed  surface  will  vary  with  the  hardness  of  the  stone  and 
the  degree  of  the  finish,  and  curves  will  cost  30  to  50  per  cent  more 
than  straight  pieces.  Hudson  River  bluestone  (sandstone)  curbing 
costs  from  20  to  40  cents  per  square  foot. 

Granite  curb  costs  from  25  to  50  cents  per  square  foot,  de- 
pending upon  locality  and  thickness. 

520.  Concrete  Curb.  In  some  sections  where  suitable  stone 
for  curbing  is  not  readily  available,  curbs  have  been  made  of  Port- 
land-cement concrete.  Owing  to  the  decreasing  price  of  cement, 
this  form  of  curb  will  doubtless  come  into  more  common  use.     It 


COMBINED  CONCRETE  CURB  AND  GUTTER. 


353 


is  usually  made  about  6  inches  thick  and  18  or  20  inches  deep.  If 
well  made,  it  does  excellently  for  residence  streets. 

For  suggestions  concerning  the  construction  of  concrete  curb, 
see  §  523-27. 

521.  GUTTERS.  Incidentally  the  construction  of  the  gutter 
has  already  been  considered  in  §  503-05,  which  see. 

Fig.  109  shows  a  concrete  gutter  used  in  St.  Louis,  Mo. 


Fig.  109.— St.  Louis  Concrete  Gutter. 

522.  COMBINED  CONCRETE  CURB  AND  GUTTER.  In  recent 
years  the  construction  of  combined  concrete  curb  and  gutter  built 
in  place  has  become  very  general  in  the  smaller  cities,  and  in  resi- 
dence districts  of  larger  cities.  Such  construction  is  cheap,  dur- 
able, efficient,  and  good  in  appearance.  It  is  very  popular  with 
brick  pavement,  and  with  asphalt  where  the  grades  are  very  flat, 
and  is   often  used    with  a   crushed-stone   pavement.      Fig.    110 


2'rvJ.J^  ^ 


mmmm^^ 


Fig.  110. -Standard  Concrete  Curb  and  Gutter. 

shows  the  cross  section  of  the  usual  form.  Fig.  Ill,  page  354, 
shows  the  form  of  combined  concrete  curb  and  gutter  employed 
in  St.  Louis,  Mo. 

523.  Foundation.  A  trench  is  excavated  4  to  6  inches  wider 
than  the  base  of  the  concrete,  and  a  layer  of  cinders  or  gravel  4  to 
8  inches  thick  (usually  6  inches)  is  laid,  flooded  with  water,  and 


354  CUKBS    AND    GUTTERS.  [CHAP.   XI. 

then  thoroughly  tamped.     Upon  this  foundation  is  erected  the 
forms  in  which  the  concrete  is  to  be  laid. 

524.  The  Forms.  There  are  two  general  methods  of  construct- 
ing these  forms:  1.  Some  contractors  lay  alternate  sections  in 
boxes  about  6  feet  long,  and  subsequently  place  boards  against 
the  sections  first  laid  and  construct  the  remaining  sections.  This 
plan  is  more  expensive  and  does  not  secure  as  good  alignment  as 


RBBBBBs 

Fig.  111.— St.  Louis  Concrete  Curb  and  Gutter. 

the  method  described  below.  2.  A  continuous  line  of  plank  is 
set  for  the  back  of  the  curb  and  another  for  the  front  of  the  gutter. 
These  plank  are  kept  in  place  by  stakes  on  both  sides.  Partitions 
are  inserted  so  as  to  divide  the  mass  into  sections  6  or  8  feet  long. 

Two  forms  of  partitions  are  in  common  use.  Sometimes  these 
partitions  are  plank  1  \  or  2  inches  thick,  in  which  case  the  sections 
are  laid  alternately,  the  partitions  being  removed  before  the  second 
series  of  blocks  are  formed.  In  other  cases,  the  partitions  are  made 
of  steel  \  or  -fa  inch  thick,  and  are  left  in  position  until  the  blocks 
are  practically  finished.  There  is  but  little  choice  between  the 
two  forms  of  partitions,  except  that  it  is  difficult  to  withdraw  the 
steel  partitions  without  chipping  the  surface  coat. 

525.  The  form  for  the  front  of  the  curb  is  made  by  setting  a 
plank  \\  or  2  inches  thick  against  the  front  of  the  upper  part  of  the 
partitions  and  clamping  it  to  the  plank  at  the  back  of  the  curb  with 
steel  screw-clamps.  Of  course,  the  lower  edge  of  this  plank  is 
rounded  to  make  the  curve  between  the  face  of  the  curb  and  the 
top  of  the  gutter. 

The  concrete  for  the  base  of  the  gutter  is  deposited  and  tamped, 
and  then  the  mortar  for  the  face  of  the  gutter  is  applied — all  before 
the  form  for  the  front  of  the  curb  is  clamped  into  place.  After 
the  plank  for  the  front  of  the  curb  is  in  place,  a  1-inch  plank  is 


COMBINED    CONCRETE    CURB   AND    GUTTER.  355 

placed  immediately  behind  it,  and  the  concrete  for  the  body  of  the 
curb  is  deposited  and  tamped.  The  1-inch  plank  is  then  carefully 
removed,  and  the  mortar  for  the  face  of  the  curb  is  put  into  the 
vacant  space.  Just  as  the  mortar  begins  to  take  its  initial  set, 
the  board  in  front  of  the  curb  is  removed,  and  the  curb  and  the 
gutter  are  troweled  smooth. 

526.  Mixing  and  Laying.  The  mortar  is  usually  one  part  of 
Portland  cement  to  H  or  2  parts  of  clean  sharp  sand. 

The  concrete  may  be  made  of  either  gravel  or  broken  stone,  the 
usual  proportions  being  either  1  part  Portland  cement,  2  parts 
sand,  and  4  parts  of  unscreened  crushed  stone,  or  1  part  cement 
and  5  or  6  parts  of  gravel.* 

To  secure  durability  it  is  necessary  that  the  surface  layer  of 
mortar  should  be  made  with  Portland  cement;  and  to  secure  a 
good  union  between  the  layer  of  mortar  and  the  concrete,  it  is 
necessary  that  the  mortar  and  the  concrete  should  be  made  with 
the  same  brand  of  cement.  Many  attempts  have  been  made  to 
lay  a  coat  of  Portland  cement  mortar  upon  a  natural  cement  con- 
crete; but  nearly  always  the  two  have  separated.  It  is  also  neces- 
sary that  the  mortar  coat  should  be  applied  as  soon  as  possible 
after  the  concrete  is  laid,  so  that  the  cement  may  set  throughout 
the  entire  mass  at  the  same  time;  otherwise  there  is  danger  of  the 
two  separating.  The  concrete  should  be  mixed  so  dry  that  little 
or  no  free  water  flushes  to  the  surface  while  it  is  being  tamped. 
If  the  water  flushes  to  the  top,  there  will  come  with  it  more  or  less 
earthy  matter  which  will  prevent  a  firm  union  of  the  mortar  and 
the  concrete. 

The  mortar  coat  should  be  mixed  rather  dry;  and  should  be 
troweled  firmly  to  give  a  dense  surface,  but  not  so  persistently 
as  to  disturb  the  initial  set. 

527.  Finishing  the  Surface.  There  is  a  difference  of  opinion 
as  to  whether  the  surface  should  be  considered  finished  when  it 
has  been  troweled,  or  whether  it  should  be  afterwards  brushed 


*  For  a  full  discussion  of  the  method  of  testing  the  cement  and  proportioning 
the  concrete,  and  of  the  relative  merits  of  gravel  and  broken-stone  concrete,  to- 
gether with  tables  of  quantities,  strength,  cost,  etc  ,  see  A  Treatise  on  Masonry 
Construction,  by  Ira  O.  Baker,  pp.  556,  6x9  inches.  John  Wiley  &  Sons,  New  York 
City.     9th  edition,  1899. 


356  CURBS   AND    GUTTERS.  [CHAP.    XI. 

with  a  slightly  wet  brush.  An  ordinary  flat  paint  brush,  with 
extra  heavy  bristles,  cut  off  about  one  inch  below  the  wood  portion, 
may  be  used  for  this  purpose.  The  objections  to  the  trowel-finished 
surface  are  that  the  trowel  marks  show  more  or  less,  and  that  the 
surface  has  a  glaze  or  shine  clearly  indicating  that  the  stone  is 
artificial;  while  the  brush  finish  has  a  uniform  dull  surface  similar 
to  a  smoothly  dressed  natural  stone.  The  objections  to  the  brush- 
finished  surface  are  that  the  brush  leaves  a  porous  surface  that  is 
not  so  durable  as  a  trowel-finished  one,  which  objection  has  con- 
siderable force  if  the  surface  is  not  first  thoroughly  troweled  and 
if  the  brush  is  not  used  lightly.  The  less  the  troweling  and  the 
more  the  brushing,  the  morj  rapidly  the  surface  can  be  finished; 
and  hence  it  is  difficult  when  brushing  is  permitted  to  prevent 
the  slighting  of  the  work.  Both  methods  of  finishing  are  employed 
by  competent  engineers. 

Recently  a  method  of  finishing  by  drawing  a  template  over 
the  curb  and  gutter  has  been  introduced.  The  few  trials  madG 
seem  to  show  that  this  method  is  r,  little  less  expensive  than  fin- 
ishing with  a  trowel,  and  that  it  gives  a  better  general  appear- 
ance and  a  better  alignment,  particularly  ct  the  joints. 

528.  Cost.  The  cost  will  depend  somewhat  upon  the  price  and 
the  quantity  of  the  labor  and  materials,  but  chiefly  upon  the  pro- 
portions of  the  mortar  and  the  concrete.  The  amount  of  cement 
required  will  vary  a  little  with  the  per  cent  of  voids  in  the  sand 
and  gravel  or  broken  stone,  but  will  depend  chiefly  upon  the  pro- 
portions of  the  mortar  and  the  concrete.  On  three  contracts  for  a 
total  length  of  about  2J  miles  of  the  form  of  combined  curb  and 
gutter  shown  in  Fig.  110,  page  353,  using  gravel  in  the  concrete, 
laid  by  two  separate  contractors,  the  length  laid  for  each  barrel 
of  Portland  cement  was  13.4,  13.44,  and  14  feet  respectively.  A 
barrel  of  cement  made  enough  1  to  1J  mortar  for  the  surface  coat 
on  33  linear  feet. 

A  yard  of  gravel  was  required  for  each  33  lineal  feet. 

The  amount  of  labor  will  vary  a  little  with  the  amount  of  exca- 
vation required  and  with  the  kind  of  forms  employed.  On  two  of 
the  contracts  referred  to  above,  one  contractor  averaged  2.25  feet 
of  completed  curb  and  gutter  per  man  per  hour,  while  the  other 
contractor  averaged  2.56  feet  per  man  per  hour.     The  latter  exca- 


COMBINED    CONCRETE    CURB   AND    GUTTER. 


357 


vated  the  trench  by  hand  before  the  roadway  was  excavated,  while 
the  former  excavated  the  roadway  and  the  gutter  with  scrapers 
before  commencing  the  construction  of  the  curb  and  gutter.  The 
curb  was  straight  and  practically  continuous.  The  working  force 
was  usually  divided  about  as  follows : 

1  foreman, 

11  men  wheeling  and  tamping  cinders, 
5  men  setting  forms, 
24  men  mixing  and  laying  concrete, 

2  men  finishing, 

3  assistant  finishers. 

The  contract  price  for  the  curb  and  gutter  referred  to  above 
was  48  cents  per  lineal  foot,  including  the  excavation  and  the  back 
filling. 

529.  Double  Curb  and  Gutter.  Fig.  112  *  shows  the  form  of 
the  concrete  double  curb  and  gutter  referred  to  in  paragraph  2 
of  §  488,  page  328. 

i*4 


Curb  \  Mtft. 


1  "'Crusted    V 


,.,'Grarel 'or Crashed /?oc/r  ... 
Fig.  112.— Double  Curb  and  Gutter. 

530.  Curb  and  Gutter  at  Private  Driveway.  Fig.  113,  page 
358,  shows  the  arrangement  of  the  combined  concrete  curb  and 
gutter  at  a  driveway  to  a  gate  or  a  building.  The  radius  of  the 
curve  at  the  corner  of  the  curb  is  too  small,  as  a  radius  of  4  or  5  feet 
would  be  better. 

531.  Merits  of  Concrete  Curb  and  Gutter.  The  advantages 
of  the  combined  concrete  curb  and  gutter  are:  1.  It  is  usually 
cheaper,  particularly  if  account  be  taken  of  the  fact  that  the  gutter 


*  Trans.  Amer.  Soc.  of  Civil  Engineers,  Vol.  42,  p.  7. 


358 


CURBS   AND    GUTTERS. 


[CHAP.  XI. 


occupies  space  that  otherwise  would  be  paved.  2.  The  alignment 
of  the  curb  is  better  and  more  permanent.  3.  The  appearance 
is  better.  4.  Usually  the  concrete  is  more  durable  than  a  natural 
stone  of  equal  cost.     5.  The  gutter  is  smooth,  and  easily  cleaned. 

A  concrete  curb  is  suitable  only  for  residence  streets,  but  is 
more  durable  for  a  business  street  than  soft  sandstone  or  lime- 
stone. 


PLAN 


Section  A-B 


Section  C-D. 

Fig.  113.— Concrete  Curb  and  Gutter  at  Private  Driveway. 


432.  OTHER  FORMS  OF  CURB.  About  1889  there  was  con- 
structed on  two  streets  at  Washington,  D.  C,  a  concrete  curb 
and  gutter  having  at  the  inner  lower  edge  of  the  curb  a  4X4  inch 
conduit  for  telegraph  and  telephone  wires,  with  hand  holes  about 


RADIUS    OF    CURB    AT    CORNER.  359 

50  feet  apart.*  The  experiment  was  not  considered  successful, 
and  the  conduit  was  never  used  for  wires. 

From  time  to  time  advertisements  appear  of  burned  clay  curbs, 
but  none  have  been  seen  which  are  not  so  thin  as  to  be  easily  broken 
and  so  constructed  by  sections  fitted  together  to  be  unstable. 

533.  Radius  of  Curb  at  Street  Corner.  As  far  as  ve- 
hicular traffic  is  concerned,  the  larger  the  radius  of  the  curb  the 
better;  but  when  the  gutter  is  carried  to  a  corner  inlet  (§  499),  it 
is  inconvenient  to  construct  or  cover  the  gutter  if  the  curved  curb 
intersects  the  sidewalk,  i.  e.,  if  the  radius  of  the  curved  curb  is  too 
great.  If  the  pavement  has  the  minimum  width,  say  18  or  20 
feet,  the  curves  of  the  corner  curbs  should  be  made  large  so  that 
a  vehicle  may  be  turned  around  at  the  street  intersection.  If  the 
curb  is  stone,  the  curved  sections  cost  considerably  more  than 
straight  ones;  and  consequently  the  less  the  amount  of  curved 
work,  i.  e.,  the  shorter  the  radius,  the  less  the  job  will  cost.  With 
concrete  curb  the  curves  cost  but  little  more  than  straight  work. 

The  radius  generally  varies  from  2  to  12  feet,  usually  from  6  to 
8.  The  corner  with  a  2-foot  radius  can  usually  be  obtained  in  one 
piece,  and  should  be  used  only  at  driveways  to  private  grounds,  at 
alleys,  and  on  unfrequented  streets  when  the  cost  of  curved  work 
is  great  and  the  amount  of  money  available  is  small.  A  radius  of 
8  or  10  feet  is  very  satisfactory.  Where  the  angle  is  more  than  90°, 
as,  for  example,  at  a  bend  in  the  street,  a  still  larger  radius  can  be 
employed. 

*  For  detailed  plans,  see  The  Technograph— the  annual  published  by  the  Associa= 
tion  of  Engineering  Societies  of  the  University  of  Illinois,— No.  5,  p.  32. 


CHAFTER  XiL 
PAVEMENT  FOUNDATIONS. 

534.  The  term  foundation  is  sometimes  applied  to  the  natural  soil 
upon  which  an  artificial  structure  rests,  and  sometimes  to  the  lower 
portion  of  the  structure  itself.  The  te'Tn  will  be  employed  here 
in  the  latter  sense,  and  the  soil  under  the  foundation  of  the  pave- 
ment will  be  referred  to  as  the  subgrade.  The  foundation  of  a 
pavement,  as  of  all  other  structures,  is  an  important  element, 
although  it  is  more  frequently  neglected  in  pavements  than  in 
other  structures. 

Art.  1.    Preparation  of  the  Subgrade. 

535.  Whatever  the  form  of  the  pavement  or  of  its  foundation,  it 
must  rest  upon  the  soil;  and  since  the  chief  office  of  the  pavement 
and  of  its  foundation  is  to  distribute  the  concentrated  load  of  the 
wheel  over  an  area  so  great  that  the  natural  soil  will  be  able  to 
support  it,  it  is  important  to  increase,  as  much  as  practicable, 
the  bearing  power  of  the  soil  by  drainage  and  by  rolling,  and 
thereby  to  decrease  the  thickness  of  pavement  required. 

536.  DRAINAGE.  The  method  of  draining  the  subgrade  of  a 
pavement  is  substantially  the  same  as  that  of  underdraining  an 
earth  road — see  §  98.  The  subgrade  of  a  pavement  requires  under- 
drainage  fully  as  much  as  does  an  earth  road,  notwithstanding 
the  fact  that  the  former  has  an  impervious  roof.  The  purpose 
of  the  underdrainage  is  to  prevent  the  surface  of  saturation  from 
rising  so  high  as  to  soften  the  subgrade.  Unless  the  subsoil  is 
very  open  and  porous,  it  is  economical  to  lay  a  tile  under  each 
edge  of  the  pavement,  2  or  3  feet  below  the  surface  of  the  sub- 
grade.  This  tile  may  empty  into  the  surface-water  catch  basins 
(§  497). 


ART.  1.]        PREPARATION  OF  THE  SUBGRADE.  361 

537.  EARTHWORK.  The  machinery  employed  in  making  exca- 
vations and  embankments  for  pavements  is  practically  the  same 
as  that  used  in  constructing  earth  roads — see  §  135-44. 

In  making  embankments  great  care  should  be  taken  to  com- 
pact them,  solid — see  Shrinkage  of  Earthwork  (§  127),  Settlement 
of  Embankments  (§  128),  Rolling  Embankments  (§  130),  and 
Stability  of  Embankment  (§  133).  For  data  on  the  Cost  of  Earth- 
work, see  §  154-76. 

The  excavation  for  pavements  is  made  by  plowing  and  then 
removing  the  earth  either  with  a  drag  or  a  wheel  scraper  (§  141), 
or  by  loading  it  into  wagons  or  carts  with  shovels.  It  is  usual 
to  specify  that  no  plowing  shall  be  allowed  within  2  inches  of 
the  subgrade,  to  prevent  the  soil  below  the  subgrade  from  being 
loosened.  If  the  subgrade  is  thoroughly  rolled,  as  described 
later,  plowing  a  little  below  the  finished  surface  is  not  a  serious 
matter;  but  if  the  subgrade  is  not  subsequently  well  rolled,  the 
loosening  of  the  soil  below  the  finished  surface  is  very  objection- 
able, since  the  foundation  will  then  have  an  uneven  hardness. 

The  subgrade  is  often  finished 
with  pick  and  shovel,  but  the 
work  can  be  done  much  more 
economically  with  the  scraping 
grader  (§  142)  or  with  the  sur- 
face grader,  Fig.  114.  The  former 
makes  a  more  uniform  surface, 
and  is  usually  more  economical; 
although  the  latter  is  an  effective 

t  T         .,-,  x1  Fig.  114.— Surface  Grader. 

implement.      In   either   case   the 

loosened  earth  must  be  hauled  away  with  scrapers  or  wagons. 

538  A  considerable  part  of  the  excavation  is  often  done  before 
the  curb  is  set,  but  the  curb  is  always  set  before  the  subgrade  is 
finished.  The  exact  position  of  the  subgrade  Is  determined  by 
stretching  a  string  transversely  across  the  street  from  curb  to  curb 
and  measuring  ordinates  similar  to  those  shown  in  the  upper  dia- 
gram of  Fig.  108,  page  347.  Some  contractors  pick  narrow  trenches 
down  to  the  subgrade  at  short  intervals  transversely  across  the 
street;  while  others  drive  stakes  with  their  tops  a  specified  dis- 
tance, say  4  or  6  inches,  above  subgrade,  and  provide  the  work- 


362  PAVEMENT  FOUNDATIONS.         [CHAP.  XII. 

men  with  a  stick  of  this  length  with  which  to  measure  down  from 
the  top  of  the  stake  to  the  subgrade.  The  former  method  must 
be  employed  when  the  scraping  grader  is  used.  The  passage  of 
the  grader  fills  the  trench  with  loose  earth,  but  it  is  easy  to  see 
the  relative  position  of  the  surface  and  the  bottom  of  the 
trench. 

539.  ROLLING  THE  SUBGRADE.  The  finished  subgrade  should 
be  thoroughly  rolled  to  consolidate  the  surface  and  also  to  discover 
any  soft  places — particularly  over  trenches  that  have  not  been 
solidly  filled.  If  the  roller  reveals  a  low  place,  it  should  be  filled 
with  earth  and  be  rolled  again.  The  roller,  whatever  its  weight, 
should  be  passed  over  the  subgrade  more  than  once,  since  the 
successive  passages  have  something  of  a  kneading  action  and  add 
to  the  solidity  of  the  soil.  Several  passes  with  a  light  roller  give 
better  results  than  a  few  passes  with  a  heavy  one.  It  is  well  to 
specify  both  the  weight  of  the  roller  and  the  number  of  times  it  is 
to  pass  over  the  road-bed.  For  some  hints  applicable  in  rolling 
the  subgrade,  see  §  326. 

It  is  customary  to  use  a  horse  roller  (§  337)  for  this  purpose, 
but  a  steam  roller  (§  338)  is  much  better  because  it  is  heavier,  and, 
still  more  important,  because  with  it  the  street  can  be  rolled  trans- 
versely. The  street  is  full  of  trenches  made  often  just  before  the 
pavement  is  laid,  in  connecting  the  houses  with  the  sewer,  the 
water,  and  the  gas;  and  as  these  trenches  run  both  longitudinally 
and  transversely,  it  is  necessary  to  run  the  roller  in  both  direc- 
tions if  the  trenches  are  certain  to  be  solidly  filled.  With  a 
horse  roller,  it  is  practically  impossible  to  roll  the  street  trans- 
versely, but  with  a  steam  roller  this  is  comparatively  easy. 

Unless  the  back-filling  of  a  trench  has  been  unusually  well 
tamped,  a  roller  run  transversely  over  a  trench  will  leave  a  de- 
pression. In  most  soils,  the  back-filling  will  not  of  itself  settle 
into  its  former  solidity,  however  long  it  is  left  to  the  action  of 
traffic  and  to  the  forces  of  nature;  and  whatever  the  foundation 
of  the  pavement,  the  heavier  traffic  is  nearly  certain  to  cause  a 
settlement  over  these  same  trenches,  unless  the  subgrade  is  well 
rolled.  Traffic  consolidates  only  a  thin  layer  near  the  surface, 
which  is  usually  removed  when  the  pavement  is  constructed. 
Ordinarily,  if  the  subgrade  is  rolled  both  longitudinally  and  trans- 


ART.   1.]  PREPARATION    OF   THE   SUBGRADE.  363 

versely  with  a  steam  roller  weighing  10  or  12  tons,  there  will  be 
no  settlement  of  the  pavement. 

In  rolling,  if  a  depression  is  produced  over  a  trench,  it  should 
be  filled  and  then  again  rolled.  If  the  depression  is  of  considerable 
depth,  it  shows  that  the  trench  was  badly  filled  or  was  very  deep, 
or  both;  and  therefore  it  is  wise  to  re-consolidate  the  trench.  One 
way  of  doing  this  is  to  make  numerous  openings  through  the  crust 
and  keep  the  depression  filled  with  water  until  the  earth  in  the 
bottom  of  the  trench  has  become  thoroughly  soaked;  and  then 
after  the  ground  has  dried  out  below,  the  roller  should  again  be 
passed  over  the  surface.  The  surest  way  to  prevent  settlement 
over  trenches  is  to  pack  the  soil  solidly  when  the  trench  is  first 
filled.  For  a  discussion  of  various  methods  of  back-filling,  see 
§540. 

Insufficient  tamping  in  filling  trenches  or  inefficient  rolling 
of  trenches  is  a  very  common  defect  in  pavement  construction, 
nearly  every  block  presenting  one  or  more  such  depressions.  One 
of  the  purposes  of  a  guarantee  of  the  pavement  (§  450)  is  to  secure 
a  thorough  consolidation  of  the  soil  in  the  trenches. 

540,  FILLING  TRENCHES.  The  back-filling  of  trenches  opened 
to  lay  water  and  gas  pipes,  to  make  house  connection  to  sewers, 
etc.,  so  that  the  road  surface  shall  be  restored  to  its  former  level 
and  remain  so,  is  a  matter  of  importance  on  both  paved  and  un- 
paved  roads — particularly  the  former.  The  failure  to  re-fill  the 
trenches  properly  is  a  source  of  annoyance  to  those  who  use  the 
road  and  of  damage  to  the  pavement  itself.  It  is  frequently 
asserted  by  those  having  opportunity  for  knowing,  that  the  dam- 
age to  pavements  through  lack  of  care  in  re-filling  trenches  and 
re-placing  the  pavements  is  greater  than  the  wear  due  to  traffic. 
No  kind  of  municipal  work  should  be  more  rigorously  inspected 
than  the  filling  of  a  trench  over  which  a  pavement  is  to  be  laid. 
The  nearly  universal  result  of  a  neglect  in  this  respect  is  thct  a 
pavement  built  at  great  expense  is  disfigured  or  damaged  by 
settlement,  the  repair  of  which  will  cost  many  times  as  much  as  it 
would  have  cost  properly  to  fill  the  trench  originally. 

The  principal  cause  of  failure  is  lack  of  care,  but  sometimes  it 
is  due  to  a  mistake  as  to  the  proper  method  to  be  employed.  A 
discriminating    judgment    is    required    to    determine    the    proper 


364  PAVEMENT   FOUNDATIONS.  [CHAP.  XIL 

method,  and  intelligence  and  faithfulness  are  necessary  in  carrying 
it  out.  There  are  several  distinct  methods  used  in  consolidating 
the  back-filling  of  trenches. 

541.  Natural  Settlement.  A  common  practice  of  those  hav- 
ing occasion  to  make  excavations  in  un paved  streets  is  to  cast 
back  loosely  the  material  taken  out,  heaping  it  into  an  unsightly 
and  annoying  ridge  over  the  trench  and  trusting  to  travel  and 
the  elements  to  restore  the  surface  to  its  original  level.  In  nearly 
pure  sand  such  a  ridge  may  in  time  settle  to  the  original  level, 
although  the  damage  due  to  the  temporary  ridge  will  generally 
be  much  more  than  the  cost  of  properly  filling  the  trench  in  the 
beginning;  but  as  a  rule  earth  loosely  put  back  will  not  attain  a 
sufficient  degree  of  compactness  to  make  it  a  safe  support  for  a 
macadam  or  other  form  of  pavement.  The  surface  may  become 
very  compact  and  hard;  and  yet  after  the  removal  of  the  foot  or 
more  of  soil,  ordinarily  necessitated  by  the  construction  of  the 
pavement,  it  will  be  found  that  the  earth  in  the  trench  will  settle 
considerably  under  a  roller  run  transversely  over  the  trench. 
$ven  though  the  surface  may  support  the  roller,  it  is  highly  prob- 
able that  ultimately  a  trench  which  has  been  loosely  filled  will 
settle  and  cause  a  depression  in  the  pavement.  This  is  proved 
by  tta  numerous  depressions  in  pavements,  and  also  by  the  fact 
that  when  trenches  loosely  filled  are  opened  years  afterwards,  it 
is  verjr  common  to  find  open  cavities.  The  promptness  with 
which  natural  settlement  takes  place  depends  upon  the  climatic 
conditions  and  the  underdrainage.  It  is  never  safe  to  depend 
upon  natural  settlement  to  secure  the  proper  compacting  of  the 
soil  in  trenches  over  which  a  pavement  is  to  be  laid,  however  long 
the  time  allowed  for  the  settlement,  and  much  less  the  few  weeks 
often  specified. 

542.  Flooding.  Where  the  water  can  be  had  cheaply,  it  is  a 
common  practice  to  attempt  to  consolidate  the  earth  in  the  trench 
by  flooding  or  puddling  it.  If  the  soil  is  sand  or  gravel  and  is  so 
pervious  that  the  trench  will  drain  out  rapidly,  thorough  flushing 
will  compact  the  material  so  that  no  trouble  will  be  experienced 
with  settlement;  but  the  flushing  must  be  done  thoroughly.  It 
is  not  sufficient  to  fill  the  trench  nearly  full  of  loose  material,  and 
then  turn  on  a  gentle  stream  of  water  until  the  trench  is  full;  for 


ART.  1.]        PREPARATION-  OF  THE  SUBGRADE.  365 

trenches  thus  filled  are  certain  to  settle  later.  The  sand  or  gravel 
should  be  added  in  layers  not  more  than  8  or  10  inches  thick,  and 
each  layer  should  be  flushed  with  a  stream  of  water  having  force 
enough  to  wash  the  finer  particles  into  the  voids  between  the 
larger  ones.  Substantially  the.  same  result  may  be  accomplished 
by  shoveling  the  sand  or  gravel  into  water  8  or  10  inches  deep;  but 
this  method  will  not  be  effective,  if  the  trench  is  filled  with  a  scraper 
cr  a  scraping  grader. 

However,  wherever  flushing  is  effective,  tamping  would  be 
equally  as  good  and  would  probably  be  less  expensive,  if  the  cost 
of  the  water  be  considered.  As  a  rule  attempting  to  consolidate 
trenches  by  flooding  is  bad  practice. 

Neither  of  the  preceding  methods  of  using  water  should  be  em- 
ployed with  clay  or  clayey  soils,  since  flushing  prevents  rather 
than  assists  the  consolidation  of  such  soils.  In  other  words, 
flushing  or  puddling  is  useful  only  with  soils  which  water  readily 
breaks  down.  If  clay  is  flooded  or  is  deposited  in  water,  the  trench 
is  filled  with  a  watery  mud  that  will  shrink  very  much  as  it  dries 
out  and  will  always  be  loose  and  porous.  It  is  well  known  that 
a  stiff-mud  brick  which  has  been  moulded  under  exceedingly 
heavy  pressure  will  shrink  in  drying  5  per  cent,  and  with  some  clays 
10  per  cent;  and  of  course  the  thin  clay  mud  in  a  flooded  trench 
will  shrink  very  much  more  than  this. 

543.  Tamping.  Except  in  the  case  of  comparatively  clean 
sand  and  gravel,  back-filling  can  be  thoroughly  done  only  by 
tamping;  and  to  make  this  method  successful  it  is  necessary  (1) 
that  the  material  shall  be  moist  enough  to  be  plastic,  but  neither 
too  wet  nor  too  dry,  (2)  that  it  shall  be  deposited  in  layers  not 
more  than  3  or  4  inches  thick,  and  (3)  that  each  layer  shall  be 
thoroughly  rolled  or  tamped.  To  secure  thorough  tamping,  the 
relative  numbers  of  tampers  and  shovelers  is  sometimes  specified; 
but  this  alone  is  ineffectual  since  there  is  a  natural  tendency  for 
the  tampers  to  work  less  energetically  than  the  shovelers,  and 
besides  more  labor  is  required  to  tamp  the  soil  around  a  pipe  than 
higher  up. 

The  amount  of  ramming  required  will  vary  with  the  character 
and  condition  of  the  soil.  Clay  and  hard  pan  should  be  moistened 
before  being  tamped,  while  clean  sand  or  clean  gravel  may  be  tamped 


366  PAVEMENT   FOUNDATIONS.  [CHAP.   XII. 

dry.  The  tamping  can  be  most  effectively  done  with  a  compara- 
tively small  light  rammer  or  tamper,  since  the  effect  of  the  blow 
is  transmitted  to  a  greater  depth,  while  a  broad  heavy  rammer 
consolidates  the  surface  only.  A  tamper  weighing  5  01  6  pounds 
is  better  than  one  weighing  20  or  25  pounds,  the  lighter  one  being 
lifted  higher  and  giving  less  fatigue  than  the  heavy  one.  It  is 
important  to  remember  that  any  amount  of  ramming  will  affect 
only  a  comparatively  thin  layer. 

Obviously  back-filling  should  not  be  attempted  when  the  ma- 
terial is  frozen,  since  subsequent  settlement  is  then  sure  to  take 
place. 

544.  To  prevent  disturbing  the  surface  of  a  pavement  plumb- 
ers, gas  fitters,  etc.,  are  sometimes  given  permission  to  tunnel 
under  the  pavement  to  make  their  connections.  This  practice 
is  never  justifiable  on  account  both  of  the  excessive  cost  and  of 
the  impossibility  of  effectively  filling  the  tunnel,  owing  to  the 
limited  space  in  which  the  work  must  be  done.  In  nearly  even- 
case  a  depression  occurs  sooner  or  later  over  the  tunnel 

545.  Replacing  All  the  Material.  The  result  to  be  obtained 
in  filling  a  trench  is  that  the  material  in  the  trench  shall  have,  the 
same  compactness  as  the  soil  around  it;  and  therefore  some  con- 
tend that  the  only  proper  way  is  to  put  back  all  the  material  taken 
out.  In  a  majority  of  cases,  this  procedure  will  secure  reason- 
ably good  results;  but  under  certain  conditions  it  will  fail.  For 
example,  the  water  pipe  or  sewer  may  occupy  a  large  proportion 
of  the  volume  of  the  trench,  and  consequently  of  necessity  there 
will  be  a  considerable  excess  of  earth.  Again,  putting  back  all 
the  earth  does  not  insure  the  restoration  of  the  original  surface 
nor  certainly  prevent  subsequent  settlement.  It  has  been  shewn 
that  soil  when  taken  from  its  natural  place  and  compacted  in 
an  embankment  will  shrink  from  8  to  15  per  cent  (see  §  127) .  and 
will  probably  subsequently  settle  2  or  3  per  cent  and  possibly  10  to 
25  per  cent  (see  §  128).  Consequently  with  a  deep  tiench  con- 
taining a  small  pipe,  it  is  possible  to  tamp  the  earth  back  so  solidly 
as  not  to  have  enough  to  restore  the  surface;  or  it  is  possible  to 
put  all  "the  soil  back  by  tamping  the  lower  portion  of  the  trench 
solidly  and  the  upper  portion  loosely,  and  still  considerable  set- 
tlement take  place.     Therefore    the    specification  to  re-place  all 


ART.   2.]  CONCRETE    FOUNDATION.  367 

of  the  material,  must  have  a  careful  and  intelligent  supervision  to 
insure  good  results. 

In  the  past  it  has  not  been  the  custom  to  fill  trenches  in  such 
a  manner  as  to  prevent  settlement;  and  therefore  if  the  best  re- 
sults are  to-be  insisted  upon,  the  specifications  should  clearly  reveal 
that  fact,  for  contractors  in  bidding  on  work  do  so  on  the  under- 
standing that  the  work  is  to  be  done  in  at  least  approximately 
the  usual  manner,  and  any  attempt  to  have  it  done  in  any  better 
way,  which  was  not  clearly  understood  from  the  beginning,  is 
likely  to.  cause  friction  and  irritation,  and  possibly  finally  to  re- 
sult in  failure. 

546.  Re-filling  with  Sand  or  Concrete.  On  account  of  the 
difficulty  of  getting  trenches  in  clay  or  loam  filled  so  that  there 
will  be  no  settlement,  it  has  been  proposed  to  require  the  trench 
to  be  filled  with  clean  sand  or  gravel.  It  is  not  known  that  this 
method  has  ever  been  tried.  It  would  probably  be  effective,  but 
usually  its  cost  would  be  prohibitive. 

In  at  least  a  few  cases  trenches  have  been  filled  with  a  fair  qual- 
ity of  natural  cement  concrete.  The  expense  for  the  concrete 
was  not  justifiable,  since  it  was  much  greater  than  that  required 
thoroughly  to  tamp  the  back-filling. 

Sometimes  municipal  authorities  are  lax  in  inspecting  the  filling 
of  trenches,  owing  to  the  belief  that  the  concrete  foundation  will 
hold  up  the  pavement  even  though  the  material  in  the  trench  may 
settle;  but  this  is  bad  practice,  since  the  ordinary  thickness  of  con- 
crete is  not  designed  to  act  as  a  bridge,  and  besides  if  it  is  thick 
enough  to  bear  up  over  trenches  it  is  needlessly  thick  elsewhere. 
With  the  usual  thickness  of  concrete  foundations,  a  depression  is 
almost  certain  to  occur  if  the  material  in  the  trench  settles;  and 
hence  the  only  safe  rule  is  to  have  the  trenches  completely  and 
compactly  filled. 

Art.  2.     Concrete  Foundation. 

547.  This  form  of  foundation  consists  of  a  layer  of  hydraulic 
cement  concrete;  it  is  absolutely  necessary  for  a  sheet  asphalt 
pavement,  and  is  frequently  used  with  wood,  brick,  and  stone- 
block  pavements.     Concrete  foundations  are  much  more  common 


368  PAVEMENT    FOUNDATIONS.  [CHAP.   XII. 

now  than  a  few  years  ago,  doubtless  partly  because  of  the  less  cost 
of  hydraulic  cement. 

The  author's  Treatise  on  Masonry  Construction*  devotes  110 
pages  to  cement,  sand,  gravel,  broken  stone,  and  concrete;  and 
therefore  the  materials  will  not  be  discussed  here,  and  the  methods 
of  mixing  and  placing  the  concrete  will  be  considered  only  as  far 
as  they  are  dependent  upon  the  particular  use  to  which  the  con- 
crete is  put.  The  above  volume  contains  detailed  explanations 
of  the  methods  to  be  used  in  testing  the  materials  of  concrete, 
discusses  the  theory  of  proportioning,  and  also  presents  numerous 
tables  showing  the  strength  and  cost  of  various  grades  of  concrete. 

548.  Advantages  of  Concrete  foundation.  The  advan- 
tages of  concrete  for  a  pavement  foundation  are:  1.  It  gives  a 
smooth  uniform  surface  upon  which  to  lay  the  pavement.  2.  It 
prevents  the  surface  water  from  percolating  to  the  subgrade.  3. 
By  its  thickness  and  resistance  to  flexure,  it  distributes  the  con- 
centrated load  over  a  considerable  area  of  the  subgrade.  4.  Con- 
crete acts  as  a  bridge  to  support  the  pavement  in  case  of  a  settle- 
ment of  the  subgrade.  5.  Being  impervious  to  water  and  a  non- 
conductor of  heat,  concrete  protects  water  and  gas  pipes  from 
freezing. 

549.  THEORY  OF  CONCRETE.  To  secure  the  greatest  strength 
at  the  least  cost,  the  proportions  of  the  concrete  should  be  so 
adjusted  that  the  voids  in  the  sand  will  be  filled  with  cement  paste, 
and  the  voids  in  the  gravel  or  broken  stone  will  be  filled  with  ce- 
ment mortar.  The  cement  is  the  most  expensive  ingredient;  and 
if  more  cement  or  more  mortar  is  used  than  is  required  to  fill  the 
voids,  the  cost  is  needlessly  great.  Again,  the  cement  is  usually 
the  weakest  ingredient;  and  hence  if  more  of  it  is  used  than  is 
necessary,  the  strength  of  the  concrete  is  thereby  decreased.  Table 
34  and  35,  pages  370-71,  from  the  author's  Treatise  on  Masonry 
Construction,  give  the  amount  of  voids  in  sand,  gravel,  and  broken 
stone. 

In  a  perfect  concrete,  every  sand  grain  will  be  coated  with 
cement  paste,  and  every  point  of  each  fragment  of  broken  stone 
will   be   covered   with   cement  mortar.     The   coating   of   cement 

*  A  Treatise  on  Masonry  Construction,  by  Ira  O.  Baker.    556  pages,  6X9  inches. 
John  Wiley  &  Sons,  New  York  City.    Ninth  Edition,  J  899. 


ART.  2.]  CONCRETE   FOUNDATION.  369 


paste  on  the  sand  grains  and  of  mortar  on  the  fragments  of  stone 
holds  the  several  pieces  apart,  and  increases  the  voids;  and  con- 
sequently it  is  not  possible  to  determine  by  computation  the  amount 
of  cement  paste  or  cement  mortar  required  to  fill  the  voids  of  any 
grade  of  broken  stone.  The  exact  proportions  required  in  any 
particular  case  can  be  determined  only  by  trial.  The  data  in 
Table  36  and  37,  pages  372-73,  from  the  author's  Treatise  on  Ma- 
sonry Construction,  were  derived  from  experiments,  and  are  suffi- 
ciently exact  for  practial  use.  These  tables  give  proportion  in 
which  the  voids  are  just  filled  when  the  mortar  or  concrete  is  com- 
pacted; and  are  very  useful  in  making  estimates. 

In  the  method  of  proportioning  implied  in  Table  36  and  37, 
the  amount  of  cement  or  mortar  will  be  stated  in  per  cent  of  the 
volume  of  the  sand  or  the  stone  depending  upon  the  proportion  of 
the  voids;  but  not  infrequently  the  proportions  of  the  concrete 
are  stated  by  volumes  independently  of  the  proportion  of  the 
voids  in  either  the  sand  or  the  broken  stone,  in  which  case  Table 
38,  page  374,  will  be  useful  in  making  estimates.  For  a  discussion 
of  the  disadvantages  of  the  latter  method  of  proportioning,  see 
pages  112^-112/  of  the  author's  Treatise  on  Masonry  Construction. 

550.  Data  for  Estimates.  Table  37  and  38,  pages  373  and  374, 
give  the  quantities  of  cement,  sand,  and  broken  stone  required  to 
make  a  cubic  yard  of  concrete,  the  first  when  the  proportions  of 
the  ingredients  are  fixed  with  reference  to  the  voids  in  the  sand 
and  stone,  and  the  second  v/hen  they  are  fixed  arbitrarily.  Each 
table  gives  the  quantities  for  unscreened  and  also  for  screened 
broken  stone;  and  Table  37  gives  also  the  quantities  of  cement 
and  gravel  required  for  a  cubic  yard  of  gravel  concrete.  The 
barrel  of  cement  in  both  tables  is  the  commercial  barrel  of  packed 
cement. 

Table  37  is  recommended  for  general  use,  since  the  proportions* 
are  more  scientific  and  more  economical.  The  first  line  gives  a 
concrete  of  the  maximum  density  and  maximum  strength,  i.  e., 
the  quantity  of  mortar  io  sufficient  to  fill  the  voids;  and  the  suc- 
cessive lines  give  concretes  of  decreasing  density  and  strength. 
The  third  and  subsequent  lines  give  concretes  containing  mortar 
equal  to  the  voids,  the  mortar  in  the  third  line  being  1  to  3,  in  the 
fourth  1  to  4,  etc. 


370 


PAVEMENT    FOUNDATIONS. 


[CHAP.   XII. 


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PAVEMENT   FOUNDATIONS. 


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ART.   2. J  CONCRETE   FOUNDATION.  375 


The  proportions  of  the  concretes  can  be  determined  by  remem- 
bering that  a  barrel  of  cement  is  equal  to  0.13  cu.yd.  For  example, 
in  the  first  line  of  Table  34  for  unscreened  broken  stone  and  Port- 
land cement,  the  0.94  bbl.  of  cement  is  equal  to  0.12  cu.  yd.;  and 
the  proportions  are:  1  volume  of  packed  cement,  2.5  volumes  of 
loose  sand,  and  7.5  volumes  of  loose  unscreened  broken  stone.  If 
it  be  assumed  that  a  barrel  of  packed  cement  will  make  1.25  barrels 
when  measured  loose,  the  above  proportions  become:  1  volume 
loose  cement,  2.0  volumes  loose  sand,  and  6.0  volumes  loose  un- 
screened broken  stone. 

551.  Screened  vs.  Unscreened  Stone.  It  is  sometimes  specified 
that  the  broken  stone  to  be  used  in  making  concrete  shall  be 
screened  to  practically  a  uniform  size;  but  this  method  is  unwise 
for  three  reasons:  1.  With  graded  sizes  the  smaller  pieces  fit  into 
the  spaces  between  the  larger,  and  consequently  less  mortar  is 
required  to  fill  the  spaces  between  the  fragments.  Therefore  the 
unscreened  stone  is  more  economical  than  the  screened.  2.  A 
concrete  containing  the  smaller  fragments  of  stone  is  stronger  than 
though  they  were  replaced  with  cement  and  sand.*  3.  A  single 
size  of  broken  stone  has  a  greater  tendency  to  form  arches  while 
being  rammed  into  place,  than  the  stone  of  graded  sizes.  In 
short,  screening  the  stone  to  nearly  one  size  is  not  only  a  needless 
expense,  but  is  also  a  positive  detriment. 

The  dust  should  be  removed,  since  it  has  no  strength  of  itself 
and  adds  greatly  to  the  surface  to  be  coated,  and  also  prevents 
the  contact  of  the  cement  and  the  body  of  the  broken  stone.  Par- 
ticles of  the  size  of  sand  grains  may  be  allowed  to  remain  if  not  too 
fine  nor  in  excess. 

552.  Portland  vs.  Natural  Cement.  It  is  sometimes  a  question 
whether  Portland  or  natural  cement  should  be  used.  As  a  rule 
this  question  should  be  decided  upon  economical  grounds,  which 
makes  it  a  question  of  relative  strength  and  relative  price.  For- 
merly prices  were  such  that  natural  cement  was  a  trifle  the  cheaper 
per  unit  of  strength;  f  but  at  present  prices  Portland  is  usually 
the  cheaper. 

♦Annual  Report  of  Chief  of  Engineers,  U.  S.  A.,  1893.  Part  3,  p  3,015:  do.  1894. 
Part  4,  p.  2,321 ;  do.  1895,  Part  4,  p.  2,953 ;  Jour,  West.  Soc.  of  Engrs,  Vol.  II.  p.  394 
Hud  400. 

f  Baker's  Masonry  Construction.  9th  edition,  p.  96-99. 


376  PAVEMENT  FOUNDATIONS.         [CHAP.  XII. 

553.  Gravel  vs.  Broken-Stone  Concrete.  There  has  been 
much  debate  as  to  the  relative  merits  of  gravel  and  broken  stone 
as  the  aggregate  for  concrete;  but  at  the  same  price  per  unit  of 
volume,  broken  stone  is  the  better.  The  reasons  for  this  are :  1 . 
The  cement  adheres  more  closely  to  the  rough  surfaces  of  the  angu- 
lar fragments  of  broken  stone  than  to  the  smooth  surface  of  the 
rounded  pebbles.  2.  The  resistance  of  concrete  to  crushing  is  due 
partly  to  the  frictional  resistance  of  one  piece  of  aggregate  to  mov- 
ing on  another;  and  consequently  broken  stone  makes  a  stronger 
concrete  than  gravel.  Experiments  show  that  concrete  made 
with  gravel  is  only  70  to  90  per  cent  as  strong  as  that  made  of 
broken  stone.* 

554.  Wet  vs.  Dry  Concrete.  There  is  considerable  diversity 
of  opinion  among  engineers  as  to  the  amount  of  water  to  be  used  in 
making  concrete.  According  to  one  extreme,  the  amount  of 
water  should  be  such  that  the  concrete  will  quake  when  tamped; 
or  in  other  words,  it  should  have  the  consistency  of  liver  or  jelly. 
According  to  the  other  extreme,  the  concrete  should  be  mixed  so 
dry  that  when  thoroughly  tamped  moisture  just  flushes  to  the 
surface.  The  advocates  of  a  wet  mixture  claim  that  it  makes  the 
stronger  and  more  dense  concrete;  while  the  advocates  of  a  dry 
mixture  claim  the  opposite.  The  difference  in  practice  is  not  as 
great  as  in  theory,  the  apparent  conflict  being  chiefly  due  to  differ- 
ences in  condition. 

It  is  unquestionably  true  that  dry  mixtures  of  neat  cement, 
and  also  of  cement  and  sand,  are  stronger  than  wet  mixtures,  pro- 
vided the  amount  of  water  is  sufficient  for  the  crystallization  of 
the  cement.  It  is  also  certainly  true  that  in  even  a  dry  mortar  or 
concrete,  the  water  is  considerably  in  excess  of  that  necessary  for 
the  crystallization  of  the  cement,  this  excess  increasing  with  the 
amount  of  sand  and  aggregate.  Of  course  an  excess  of  water  is 
an  element  of  weakness.  But  the  amount  of  water  to  be  used  in 
making  concrete  is  usually  a  question  of  expediency  and  cost,  and 
not  a  question  of  the  greatest  attainable  strength,  regard  J  ess  of 
expense. 

In  using  concrete  for  pavement  foundations  the  following  items 

*  Baker's  Masonry  Construction,  9th  edition,  p.  109. 


ART.   2. J  CONCRETE   FOUNDATION".  377 

are  worthy  of  consideration:  1.  Wet  concrete  contains  a  gieat 
number  of  invisible  pores,  while  dry  concrete  is  likely  to  contain  a 
considerable  number  of  visible  voids;  and  for  this  reason  there  is 
liability  that  wet  concrete  will  be  pronounced  the  more  dense,  even 
though  both  have  the  same  density.  2.  Wet  concrete  is  more 
easily  mixed;  and  therefore  if  the  concrete  is  mixed  by  hand  and 
the  supervision  is  insufficient  or  the  labor  is  careless,  or  if  the  ma- 
chine by  which  it  is  mixed  is  inefficient,  wet  mixtures  are  to  be 
preferred.  3.  Wet  mixtures  can  be  compacted  into  place  with 
less  effort  than  dry;  but  on  the  other  hand  the  excess  of  water 
makes  the  mass  more  porous  than  though  the  concrete  had  been 
mixed  dry  and  thoroughly  compacted  by  ramming.  Dry  con- 
crete must  be  compacted  by  ramming,  or  it  will  be  weak  and  por- 
ous; but  if  the  concrete  is  mixed  wet  the  stones  by  their  weight 
will  bury  themselves  in  the  mortar,  and  the  mortar  by  its  fluidity 
will  flow  into  the  voids.  4.  A  rich  concrete  can  be  compacted 
much  easier  than  a  lean  one,  owing  to  the  lubricating  effect  of  the 
mortar,  and  hence  a  rich  concrete  can  be  mixed  dryer  than  lean 
ones.  The  quaking  of  concrete  frequently  is  due  more  to  an 
excess  of  mortar  than  to  an  excess  of  water.  5.  Lean  concretes 
should  be  mixed  dry,  since  if  wet  the  cement  will  find  its  way  to  the 
bottom  of  the  layer  and  destroy  the  uniformity  of  the  mixture. 
6.  Machine-made  concrete  may  be  mixed  dryer  than  hand-made, 
owing  to  the  more  thorough  incorporation  of  the  ingredients.  7. 
Gravel  concrete  can  be  more  easily  compacted  than  broken  stone, 
and  hence  may  be  mixed  dryer.  8.  In  mixing  dry  by  hand  there 
is  a  tendency  for  the  cement  to  ball  up,  or  to  form  nodules  of  neat 
cement,  while  in  mixing  wet  this  does  not  occur. 

The  conclusion  is  that  sometimes  wet  concrete  must  be  used 
regardless  of  any  question  of  strength  and  cost;  while  with  thor- 
ough mixing  and  vigorous  ramming,  dry  concrete  is  strongest  but 
also  most  expensive  to  mix  and  lay. 

555.  Proportions.  The  usual  proportions  of  concrete  em- 
ployed for  foundations  of  pavements  are:  with  natural  cement, 
1  part  cement,  2  parts  sand,  and  3  to  5,  usually  4,  parts  broken 
stone  or  gravel;  and  for  Portland  cement,  1  part  cement,  2  or  3 
parts  sand,  and  5  to  8  parts,  usually  5  or  6,  of  broken  stone. 

The  proportions  of  the  concrete  in  a  measure  depend  upon  the 


378  PAVEMEXT  FOUNDATIONS.         [CHAP.  XII. 


thickness  of  the  foundation.  The  purpose  of  the  foundation  is  to 
distribute  the  concentrated  pressure  of  the  wheel  over  an  area  of 
the  subgrade  so  great  that  the  soil  can  support  the  load;  and  this 
distribution  can  be  obtained  by  varying  either  the  strength  or  the 
thickness  of  the  concrete.  Therefore  the  engineer  may  use  a  thin 
bed  of  rich  concrete  or  a  thick  bed  of  lean  concrete.  The  combina- 
tion to  be  used  in  any  particular  case  will  depend  upon  the  relative 
strength  of  the  different  grades  of  concrete  and  upon  the  prices 
of  the  several  ingredients.  In  some  cases  it  may  be  economical 
to  use  a  thicker  layer  of  broken  stone  without  any  cement  at  all 
(see  §  562).  However,  if  a  layer  of  broken  stone  is  employed  for  a 
pavement  foundation,  it  should  be  compacted  by  rolling  until  the 
fragments  do  not  move  under  the  foot  in  walking  over  it. 

556.  THICKNESS.  The  thickness  of  the  concrete  foundation 
for  light  traffic  is  nearly  always  6  inches,  and  for  very  heavy 
traffic  8  inches. 

557.  MIXING  THE  CONCRETE.  The  value  of  the  concrete  de- 
pends greatly  upon  the  thoroughness  of  the  mixing.  Every  grain 
of  sand  and  every  fragment  of  aggregate  should  have  cement  adher- 
ing to  every  point  of  its  surface.  Thorough  mixing  should  cause 
the  cement  not  only  to  adhere  to  all  the  surfaces,  but  should  force 
it  into  intimate  contact  at  every  point.  It  is  possible  to  increase 
the  strength  of  really  good  concrete  100  per  cent  by  prolonged 
trituration  and  rubbing  together  of  its  constituents.  The  longer 
and  the  more  thorough  the  mixing  the  better,  provided  the  time 
of  mixing  does  not  trench  upon  the  time  of  set,  or  the  working 
does  not  break  and  pulverize  the  angles  of  the  stone.  *  Further, 
uniformity  of  mixture  is  as  important  as  intimacy  of  contact  be- 
tween the  ingredients.  Of  course  thoroughness  of  mixing  adds  to 
the  cost,  and  it  may  be  wiser  to  use  more  cement  or  more  con- 
crete, and  less  labor. 

Concrete  may  be  mixed  by  hand  or  by  machinery  The  latter 
is  usually  the  better  method;  since  the  work  is  more  thoroughly 
and  more  quickly  done,  and  since  ordinarily  the  ingredients  are 
brought  into  more  intimate  contact  But  the  concrete  employed 
for  pavement  foundations  is  usually  mixed  by  hand,  apparently 
because  either  of  the  expense  of  transporting  the  concrete  con- 
siderable distances,  or  of  the  difficulty  of  continually  moving  the 


ART.  2.]  CONCRETE    FOUNDATION.  372 

mixing  machine.  However,  several  machines  have  been  intro- 
duced very  recently  which  give  promise  of  success  in  mixing  con- 
crete for  pavement  foundations. 

The  concrete  is  usually  mixed  on  a  board  platform  8  or  10  feet 
square,  although  a  metal  plate,  T3g-  to  f  inch  thick,  possesses  some 
decided  advantages.  It  lasts  longer,  is  easier  to  shovel  from  and 
to  wheel  upon.  The  ingredients  of  the  concrete  are  stored  on 
the  parking  or  in  the  space  to  be  paved.  If  the  materials  are  hauled 
upon  the  subgrade  after  it  is  finished,  it  will  usually  be  necessary 
to  cover  the  trackway  with  plank  to  prevent  cutting  up  the  sub- 
grade.  The  materials  of  the  concrete  are  wheeled  upon  the  mixing 
board,  mixed,  and  cast  with  shovels  directly  into  place. 

The  mixing  is  usually  done  about  as  follows:  The  sand  to  be 
mixed  in  a  batch  of  mortar  is  spread  evenly  over  the  middle  of  the 
mixing  board,  and  the  dry  cement  is  spread  evenly  over  the  sand, 
then  the  two  are  thoroughly  mixed  with  hoes  or  shovels.  As  the 
mixing  proceeds  the  necessary  water  is  added,  preferably  with  a 
spray  to  secure  greater  uniformity  and  to  prevent  the  washing 
away  of  the  cement.  The  mass  should  be  worked  until  it  is  of  a 
uniform  consistency.  The  broken  stone,  having  previously  been 
sprinkled  but  having  no  free  water  in  the  heap,  is  next  added.  The 
whole  is  then  turned  until  every  fragment  is  covered  with  cement. 

Some  contractors  use  shovels  instead  of  hoes,  claiming  that  the 
former  are  more  economical.  The  effectiveness  of  the  shovel 
varies  greatly  with  the  manner  of  using  it.  It  is  not  sufficient 
simply  to  turn  the  mass;  but  the  sand  and  cement  should  be 
allowed  to  run  off  from  the  blade  in  such  a  manner  as  thoroughly 
to  mix  them.  It  is  difficult  to  get  laborers  to  do  this  with  the 
shovel,  which  is  one  reason  why  many  contractors  prefer  hoes. 
When  it  is  supposed  the  mixing  will  be  done  with  shovels,  the  num- 
ber of  times  the  material  shall  be  turned  is  specified;  but  the  speci- 
fication is  not  definite,  since  so  much  depends  upon  the  manner  of 
doing  the  work.  Often  it  is  specified  that  the  sand  and  cement  shall 
be  turned  twice,  and  that  the  mortar  and  stone  shall  be  turned  four 
times  exclusive  of  casting  into  place.  The  concrete  appears  wetter 
each  time  it  is  turned,  and  should  appear  too  dry  until  the  very  last. 

558.  LAYING  THE  CONCRETE.  After  being  mixed  the  concrete 
is  shoveled  from  the  boards  into  place.     The  proper  thickness  of  the 


380  PAVEMENT  FOUNDATIONS.         [CHAP.  XII. 

layer  is  indicated  either  (1)  by  the  tops  of  small  stakes  driven  at 
intervals  of  4  or  5  feet  each  way,  whose  position  is  determined  by 
measuring  down  from  a  string  stretched  from  curb  to  curb  (see 
Fig.  108,  page  347),  or  (2)  by  a  curved  template  having  one  end 
upon  the  curb  and  the  other  end  upon  the  opposite  curb  or  upon  a 
scantling  near  the  middle  of  the  street.  The  concrete  is  brought 
to  the  proper  elevation  with  a  shovel  or  a  rake,  and  then  tamped. 

The  rammer  usually  employed  consists  of  a  block  of  iron  or  a 
stick  of  wood  6  to  8  inches  square,  weighing  from  20  to  40  pounds. 
The  concrete  should  be  tamped  until  mortar  flushes  to  the  top, 
which  secures  a  smooth  surface  and  guarantees  that  the  mass  has 
been  thoroughly  consolidated.  There  are  two  tricks  sometimes 
employed  to  make  it  appear  that  this  condition  has  been  fulfilled. 
One  is  to  scrape  off  the  mortar  left  adhering  to  the  mixing  board 
and  throw  it  on  top  of  the  concrete  already  in  place.  The  other 
is  to  shovel  the  concrete  up  higher  than  the  finished  surface  and 
then  bring  it  down  with  a  rake,  the  stones  being  pulled  out  and  the 
mortar  left  on  top.  Of  course  neither  of  these  tricks  should  be 
accepted  a»  a  substitute  for  the  proper  amount  of  tamping. 

Not  infrequently  loose  fragments  of  stone  are  left  upon  the  top 
of  the  foundation.  If  the  concrete  is  well  mixed  and  well  tamped, 
there  will  be  no  pieces  left  on  its  surface ;  and  if  they  are  left  there, 
they  should  be  carefully  picked  off,  since  otherwise  the  paving- 
blocks  will  not  have  a  firm  even  bearing  on  the  concrete.  In  Eng- 
land the  top  of  the  concrete  is  floated  with  a  thin  film  of  either  neat 
cement  or  rich  mortar  to  secure  a  perfectly  smooth  surface  upon 
which  to  place  the  wood  paving-blocks. 

When  finally  completed  the  concrete  should  be  covered  with 
sand,  say  an  inch  deep,  to  keep  it  from  drying  out.  If  the  water  is 
evaporated  instead  of  uniting  with  the  cement,  the  concrete  will  be 
materially  weakened;  concrete  stored  in  a  steam-heated  room  will 
attain  to  only  about  half  the  strength  of  cubes  stored  in  water. 
Therefore  if  the  weather  is  warm  and  dry,  the  sand  covering  the 
concrete  should  be  sprinkled  at  intervals  to  keep  it  damp.  No 
teaming  or  walking  on  the  concrete  should  be  permitted  until  it  has 
firmly  set — which  is  usually  assumed  to  require  from  4  to  10  days, 
depending  on  the  activity  of  the  hydraulic  cement  used.  With 
reasonable  care  and  ordinary  cement,  the  pavement  may  be  laid 


ART.  2.]  CONCRETE   FOUNDATION.  381 

four  or  five  days  after  the  concrete  is  placed,  although  many  en- 
gineers to  be  on  the  safe  side  wait  8  or  10  days.  The  fact  that  the 
street  is  closed  for  a  considerable  time  to  allow  the  concrete  to  set, 
is  the  only  objection,  except  possibly  the  cost,  to  this  form  of  foun- 
dation. 

559.  Cost  of  Concrete.  The  cost  of  the  materials  varies 
with  the  locality  and  the  conditions  of  the  markets;  and  hence  it 
is  unwise  to  cite  examples  or  to  attempt  any  generalizations.  When 
the  prices  are  known  estimates  may  be  easily  prepared  by  the  use 
of  Tables  36  and  37  or  38.  pages  372,  373,  374. 

560.  For  detailed  data  on  the  cost  of  mixing  and  laying  concrete 
in  miscellaneous  engineering  construction,  see  the  author's  Treatise 
on  Masonry  Construction,  pages  112?;-112z.  The  following  relate 
to  the  cost  of  mixing  and  laying  concrete  for  pavement  foundations, 

In  a  small  western  city  the  average  cost  to  the  contractor  of 
mixing  and  laying  a  thickness  of  6  inches  of  concrete  during  two 
years  was  about  7  cents  per  square  yard,  for  1  part  cement,  2  parts 
sand,  and  4  parts  broken  stone,  turned  six  times  exclusive  of 
casting  into  place.  With  gravel  instead  of  broken  stone,  the  cost 
was  about  6  cents  per  square  yard;  and  with  four  turnings  instead 
of  six,  the  cost  was  about  half  a  cent  less  than  the  prices  above. 
All  the  mixing  was  done  with  shovels.  The  wages  of  common 
laborers  was  $1.50  for  10  hours. 

In  a  large  western  city  the  average  cost  to  various  contractors 
of  mixing  and  laying  a  thickness  of  6  inches  of  concrete  was  5^ 
cents  per  square  yard.  The  mixing  was  done  with  hoes,  the  specifi- 
cations requiring  that  the  concrete  should  be  mixed  until  each 
particle  of  the  stone  was  completely  covered  with  mortar.  The 
wages  of  common  laborers  was  $1.50  for  10  hours. 

The  following  example*  gives  the   distribution  of  the  labor 

of  laying   a  6 -inch   concrete   pavement  foundation,  in  hours  per 

square  yard. 

4  men  filling  barrows  with  sand  and  stone 0.15 

10  men  wheeling,  mixing,  and  shoveling  to  place  (3  or  4  steps) 0.37 

2  men  ramming 0 .  07 

1  water  boy,  equivalent  in  common  labor 0 . 01 

1  foreman,  equivalent  in  common  labor 0 .  06 

Total  hours  per  sq.  yd 0 .  67 

*  Engineering  News,  Vol.  46,  p.  424— Dec.  5,  1901-j 


382  PAVEMENT  FOUNDATIONS.         [CHAP.  XII. 

The  sand  and  stone  were  dumped  in  the  street  upon  boards,  and 
were  hauled  in  wheel-barrows  about  40  feet  to  the  mixing  boards. 
The  mortar  was  turned  three,  and  the  stone  three  or  four  times. 
Two  gangs  under  separate  foremen  worked  side  by  side  in  the 
same  street. 

The  same  correspondent  gives  another  example  which  required 
0.58  hours  per  sq.  yd.,  in  which  case  the  mortar  was  turned  only 
once  and  the  stone  twice,  water  being  used  in  abundance. 

The  cost  of  labor  in  mixing  and  laying  concrete  is  often  8  or  9 
cents  a  square  yard.  For  the  most  economical  work  the  sand  and 
stone  should  be  deposited  in  ridges  on  the  subgrade  near  the  middle 
of  the  street;  and  if  they  are  piled  on  the  parking,  the  cost  will  be 
considerably  greater  than  above. 

561.  Portable  concrete-mixing  machines  have  been  tried  for 
pavement  foundations,  but  have  not  been  very  successful.  Appar- 
ently the  hand  labor  required  with  the  machine  is  about  equivalent 
to  that  required  to  mix  the  concrete  by  hand  directly;  in  other 
words,  the  cost  of  shoveling  the  ingredients  from  the  ground  up  and 
into  the  machine  is  about  equivalent  to  the  cost  of  mixing  by  hand. 
Of  course,  with  a  machine,  interest  and  depreciation  will  amount 
to  considerable  particularly  as  the  machine  will  probably  be  in  use 
only  a  comparatively  few  days  during  the  year.  However,  two 
or  three  concrete-mixing  machines  have  recently  been  introduced 
which  give  promise  of  success  for  pavement  work. 

Art.  3.     Miscellaneous  Foundations. 

562.  MACADAM.  Where  crushed  stone  is  especially  plentiful 
or  cement  is  unusually  expensive,  a  thick  course  of  macadam  may 
be  more  economical  than  a  thin  layer  of  concrete  Concrete  dis- 
tributes the  concentrated  load  of  the  wheel  over  a  considerable  area 
of  the  subgrade  by  virtue  of  both  its  thickness  and  its  transverse 
strength;  while  macadam  distributes  the  pressure  only  by  virtue 
of  its  thickness.  Therefore  if  the  cement  is  omitted  the  thickness 
of  the  broken  stone  should  be  increased.  The  efficiency  of  a  layer 
of  broken  stone  in  distributing  the  concentrated  "oad  on  a  wheel  is 
proved  by  the  fact  that  under  very  favorable  circumstances  4  inches 
of  macadam  has  successfully  carried  a  considerable  traffic  (§  321), 


ART.   3.]  MISCELLANEOUS   FOUNDATIONS.  383 

while  6  inches  of  macadam  are  quite  common  (§  320).  If  4  or  6 
inches  of  macadam  without  any  other  pavement  will  carry  the 
traffic,  the  same  thickness  will  certainly  make  a  good  foundation 
for  a  pavement  of  brick,  or  wood,  or  stone  blocks. 

A  macadam  foundation  should  be  laid  substantially  as  the  lower 
course  of  a  macadam  road  (§  339).  The  rolling  should  be  continued 
until  the  stones  are  firm  under  foot  as  one  walks  over  the  layer.  If 
the  stone  is  soft  (there  is  no  objection  to  a  moderately  soft  stone 
for  this  purpose) ,  the  rolling  will  crush  the  top  of  the  layer  to  such 
an  extent  that  the  surface  will  be  nearly  impervious.  If  the  wear- 
ing surface  of  the  pavement  is  not  too  impervious,  or  if  the  drainage 
of  the  subsoil  is  not  good,  or  if  for  any  other  reason  it  is  desired  to 
make  the  foundation  impervious,  it  may  be  done  by  spreading  stone 
dust  upon  the  rolled  macadam  and  continuing  the  rolling  with  or 
without  sprinkling. 

563.  BITUMINOUS  CONCRETE.  In  England  a  mixture  of 
broken  stone  and  tar,  often  called  bituminous  concrete,  is  some- 
times used  as  a  foundation  The  only  advantage  claimed  for  it  is 
that  the  pavement  may  be  laid  as  soon  as  the  foundation  is  com- 
pleted and  therefore  it  is  more  suitable  for  busy  thoroughfares  than 
hydraulic  cement  concrete.  The  bituminous  concrete  is  sometimes 
laid  as  described  in  §  709,  and  sometimes  by  spreading  and  rolling 
the  broken  stone,  and  pouring  tar  *  over  the  surface  and  then  cover- 
ing that  with  a  thin  layer  of  small  stones  and  finally  rolling.  This 
foundation  is  more  expensive  and  less  reliable  than  hydraulic 
cement  concrete 

Asphalt  may  be  used  instead  of  coal  or  gas  tar,  but  it  will  not 
adhere  to  the  stone  unless  both  are  at  a  higher  temperature  than 
that  of  the  ordinary  atmosphere.  For  a  method  of  heating  and 
mixing  stone  and  asphalt,  see  §  600.  On  account  of  the  expense 
asphaltic  concrete  is  seldom  used  for  a  pavement  foundation. 

564.  GRAVEL.  Sandy  gravel  is  sometimes  used  as  a  foundation 
for  pavements — particularly  brick  and  wood  block.  The  proper 
thickness  of  the  layer  depends  upon  the  nature  of  the  soil  and  the 
thoroughness  of  the  underdrainage ;  but  it  is  usually  6  or  8  inches. 
It  is  customary  to  dump  the  gravel  upon  the  subgrade  directly  from 


*  Often  referred  to  in  British  engineering  literature  as  a  mixture  of  pitch,  tar, 
ani  creosote  oiL;  and  often,  but  improperly,  called  asphalt  or  asphaltic  cement. 


384  PAVEMENT   FOUNDATIONS.  [CHAP.  XII. 

wagons,  and  then  to  level  off  between  the  piles  with  shovels.  By 
this  process  the  bottom  of  the  original  piles  is  much  more  compact 
than  the  space  between  the  piles ;  and  rolling  does  not  materially 
lessen  the  inequalities,  since  the  roller,  being  usually  a  single  cylinder 
of  considerable  length  (§  336),  riaes  upon  the  top  of  the  piles  and 
does  not  compress  the  gravel  between  them.  The  result  is  that 
soon  after  the  pavement  is  completed,  the  natural  settlement  of 
the  gravel  foundation  causes  the  surface  to  be  full  of  depressions. 

The  better  and  cheaper  method  is  to  level  off  the  piles  with  a 
scraping  road  grader  (§  142),  and  then  thoroughly  harrow  the 
gravel  with  a  long-tooth  harrow,  after  which  the  foundation  should 
be  rolled.  For  the  best  results,  the  gravel  should  be  spread  in 
layers  not  more  than  2  or  3  inches  thick.  Brick  pavements  upon 
gravel  foundation  laid  by  this  method  have  shown  no  depressions 
after  many  years,  while  those  constructed  with  the  utmost'  care  by 
the  preceding  method  with  the  same  gravel  on  the  same  soil  have 
been  full  of  holes. 

565.  SAND.  A  stone-block  and  also  a  wood-block  pavement  is 
sometimes  laid  on  a  bed  of  sand.  With  stone  blocks  the  sand  is 
used  more  as  a  material  in  which  to  bed  the  blocks  so  as  to  make 
the  upper  surface  of  the  pavement  even,  than  as  a  foundation 
proper,  the  sand  being  simply  a  loose  bed  in  which  holes  may  be 
easily  dug  to  receive  the  deeper  blocks  and  from  which  material 
may  be  obtained  to  fill  up  under  the  shorter  blocks. 

566.  PLANK.  A  wood-block  pavement  is  sometimes  laid  on  a 
coarse  of  plank  upon  a  bed  of  sand  or  gravel.  The  gravel  or  sand 
should  be  laid  substantially  as  described  in  §  564.  The  conditions 
that  should  be  fulfilled  by  the  plank  will  be  considered  in  Chapter 
XVII— Wood-Block  Pavements. 


CHAPTER  XIII. 
ASPHALT  PAVEMENTS. 

Art.  1.    The  Asphalt. 

568.  NOMENCLATURE.  Asphalt  exists  in  various  forms  over 
widely  distributed  parts  of  the  earth,  and  has  been  in  somewhat- 
common  use  for  different  purposes  since  the  dawn  of  history;  con- 
sequently the  terms  employed  to  designate  it  have  been  varied,  and 
recently  there  has  been  no  little  confusion  in  the  nomenclature,  due 
in  no  small  part  to  conflicting  commercial  interests.  The  following 
definitions  are  believed  to  be  generally  accepted,  and  are  suffi- 
ciently exact  for  present  purposes. 

569.  Bitumen.  A  natural  hydro-carbon  mixture  of  mineral 
occurrence,  widely  diffused  in  a  variety  of  forms  which  grade  by 
imperceptible  degrees  from  a  light  gas  to  a  solid,  sometimes  found 
in  a  pure  state  but  usually  intermixed  with  organic  and  inorganic 
matter.  The  bitumen  series  includes  the  following,  in  order  of  their 
density:  natural  gas,  natural  naptha,  petroleum,  maltha  (at  ordi- 
nary temperatures  soft  and  sticky),  asphalt  (at  ordinary  tempera- 
tures stiff  and  non -sticky),  glance  pitch  (dry  and  brittle). 

570.  Asphalt.  A  general  name  for  the  solid  forms  of  natural 
mineral  bitumen.  Asphalt  is  distinguished  from  coal  in  being 
soluble  in  bisulphide  of  carbon  and  in  benzole.  Coal,  peat,  etc.,  are 
ruled  pyro-bitumens  because  they  yield  an  artificial  bitumen  by 
distillation.  Asphalt  is  usually  found  associated  with  various 
mineral  and  organic  substances.  Asphalt  is  sometimes  popu- 
larly called  mineral  pitch  and  mineral  tar :  and  different  varieties  of 
asphalt  are  called  grahamite,  albertite,  gilsonite,  wurtzelite,  uinta- 
tite,  turrellite,  etc. 

The  term  asphalt  is  the  English  equivalent  of  asphaltum.  the 
Latin  fonn.     Asphalt  and  bitumen  are  frequently  used  synony- 

385 


386  ASPHALT    PAVEMENTS.  [CHAP.   XIII. 

mously,  but  usually  in  paving  literature  bitumen  is  employed  to 
designate  the  valuable  hydro-carbon  compounds  in  the  native 
asphalt.* 

571.  Crude  Asphalt.  The  native  mixture  of  bitumen,  sand, 
clay,  water,  organic  matter,  etc. 

572.  Refined  Asphalt.  The  native  mixture  after  it  has  been 
freed  wholly  or  in  part  from  water  and  organic  and  inorganic  matter 
by  being  heated.  Commercial  refined  asphalt  contains  considerable 
earthy  matter;  in  fact  commercial  refining  consists  virtually  in 
driving  off  the  water  and  volatile  oils,  and  incidentally  in  removing 
a  little  earthy  matter. 

]  573.  Rock  Asphalt.  A  limestone  or  sandstone  naturally  im- 
pregnated with  asphalt.  Rock  asphalt  is  the  principal  form  of 
asphalt  used  in  Europe  for  paving  purposes,  and  is  usually  there 
designated  as  asphalt.  Some  European  commercial  interests  insist 
that  only  rock  asphalt  is  entitled  to  be  called  asphalt. 

574.  Asphaltic  or  Bituminous  Limestone.  A  limestone  natu- 
rally impregnated  with  asphalt. 

575.  Asphaltic  or  Bituminous  Sandstone.  A  sandstone  natu- 
rally impregnated  with  asphalt. 

576.  Compressed  Asphalt.  In  Europe,  particularly  in  France, 
a  rock-asphalt  pavement  is  frequently  referred  to  as  being  made  of 
compressed  asphalt,  or,  in  French,  asphalte  comprime. 

577.  Asphalt  Mastic.  A  term  frequently  applied  to  refined 
asphalt,  particularly  to  that  obtained  from  bituminous  rocks,  and 
is  usually  in  the  form  of  cakes,  which  are  melted  and  mixed  with 
sand  and  used  for  making  pavements  and  sidewalks,  chiefly  the 
latter  (see  §  919). 

578.  Asphaltic  Cement.  Refined  asphalt  which  has  been  mixed 
with  some  solvent  to  increase  its  plasticity,  adhesiveness,  and 
tenacity. 

579.  Asphalt  Pavement.  A  pavement  composed  of  sand  or 
pulverized  stone  held  together  by  asphalt.  In  America  an  asphalt 
pavement  is  ordinarily  understood  to  be  a  comparatively  thin  layer 
of  sand  held  together  by  asphalt  laid  upon  a  bed  of  hydraulic 


*  For  a  scientific  classification  of  hydro-carbons  and  allied  substances  and  also 
for  a  classification  of  bituminous  compounds  which  employs  neither  asphalt  nor 
bitumen,  see  Annual  Report  U.  S.  Geological  Survey,  1900-01,  Part  I,  p.  220. 


ART.   1.]  THE   ASPHALT.  387 

cement  concrete;  but  in  Europe  the  term  asphalt  pavement  is 
understood  to  be  a  comparatively  thick  layer  of  asphaltic  lime- 
stone or  asphaltic  sandstone;  with  or  without  a  hydraulic  concrete 
base. 

580.  Asphaltic  Concrete.  Broken  stone  bound  together  with 
asphaltic  cement. 

581.  Asphalte  Comprime.  The  French  equivalent  of  com- 
pressed asphalt — see  §  576.  This  term  is  employed  to  indicate  that 
the  material  is  compressed  in  place;  in  contradistinction  to  being 
simply  applied  with  a  trowel. 

582.  Asphalte  Coute:  The  French  equivalent  of  asphaltic 
mastic — see  §  577.  It  is  applied  with  a  trowel  without  other  com- 
pression. 

583.  General  Characteristics.  As  usually  found  asphalt 
is  of  a  dark  brown  or  glistening  black  color.  It  varies  in  hardness 
from  a  viscous  liquid  to  about  3J  on  the  Dana  scale.  The  streak 
is  almost  uniformly  brown,  sometimes  brownish-black;  and  the 
fracture  is  dull  and  conchoidal.  When  rubbed  or  freshly  broken,  it 
emits  a  peculiar  bituminous  odor,  which  is  not  disagreeable  although 
a  little  sour  smelling.  Before  the  blow-pipe,  the  solid  varieties  are 
quickly  melted;  and  all  are  readily  evaporated  and  burned,  and 
leave  as  ash,  the  organic  and  inorganic  impurities,  which  are  usually 
found  in  it  in  smaller  or  larger  quantities.  Its  specific  gravity  in 
the  natural  state  varies  from  0.96  to  1.68  according  to  its  porosity 
and  the  amount  and  the  character  of  the  impurities  present.  It  is 
insoluble  in  water,  but  is  more  or  less  soluble  in  carbon  bisulphide, 
alcohol,  turpentine,  ether,  naptha,  and  petroleum. 

Coal-tar,  or  gas-tar,  has  an  appearance  somewhat  like  asphalt, 
and  is  sometimes  used  as  a  substitute  for  it  or  as  an  adulterant.  Tar 
is  not  so  valuable  for  paving  purposes  as  asphalt,  since  it  more  easily 
loses  its  cementing  qualities  by  vaporization  and  oxidation.  The 
principal  method  of  distinguishing  asphalt  and  coal-tar,  available 
to  the  layman,  is  the  odor.  The  tar  emits  a  sharp,  acrid  odor;  while 
both  the  crude  and  the  refined  asphalt  when  cold  give  a  weak  clay 
like  odor,  and  must  be  rubbed  to  obtain  the  distinctive  bituminous 
odor.  If  tar  is  mixed  with  asphalt,  the  presence  of  25  per  cent  will  be 
revealed  by  the  odor.  This  is  the  proportion  of  tar  in  the  vulcanite 
or  coal-tar  pavements  laid  in  Washington  from  1877  to  1887.  When 


388  ASPHALT    PAVEMENTS.  [CHAP.  XIII. 

being  laid,  tar  gives  off  a  bluish  vapor,  while  asphalt  emits  a  white 
vapor.  Expert  analysis  is  necessary  to  detect  the  presence  of  tar 
when  mixed  with  asphalt  in  small  quantities.  The  following 
method  will  certainly  detect  5  to  7  per  cent  of  tar.  "Extract  the 
bitumen  with  carbon  disulphide,  filter,  evaporate  to  dryness,  and 
heat  the  residue  till  it  can  be  ground  to  a  dry  powder;  0.1  gram  is 
treated  with  5  c.c.  of  fuming  sulphuric  acid  for  24  hours  and  is  then 
mixed  by  continuous  stirring  with  10  c.c.  of  water.  If  coal-tar  be 
present,  the  solution  will  be  of  a  dark  brown  or  blackish  tint;  if  not. 
the  solution  will  be  of  a  light  yellowish  color.' ' 

584.  Asphalt  limestone  varies  in  color  from  chocolate  brown  to 
black  when  freshly  broken,  the  color  being  darker  as  the  proportion 
of  asphalt  is  greater.  The  percentage  of  asphalt  permeating  the 
limestone  varies  in  different  deposits  and  in  different  parts  of  the 
same  mine,  usually  ranging  from  1  to  20  per  cent.  The  fracture  of 
asphaltic  limestone  is  irregular,  and  the  grain  is  very  fine.  Under 
the  microscope  the  smallest  particle  is  coated  with  asphalt.  If  cut 
by  a  sharp  blow  of  an  axe,  it  appears  grayish  white  along  the  cut, 
due  to  the  forcing  out  of  the  asphalt  and  the  leaving  of  the  particles 
of  limestone  exposed.  If  a  piece  contains  about  10  per  cent  of 
asphalt,  it  can  be  warmed  and  broken  in  the  hands,  and  a  piece 
heated  over  the  fire  falls  apart;  and  if  heated  in  a  pan  and  held  for  an 
hour  at  a  high  temperature,  the  asphalt  is  driven  off,  and  a  gray, 
powdered  limestone  remains.  If  a  sample  contains  more  than 
about  4  per  cent  of  asphalt,  a  bituminous  odor  is  perceptible  when 
the  piece  is  freshly  broken. 

585.  Asphaltic  sandstone  contains  from  1  to  70  per  cent  of 
asphalt.  The  grain  is  sometimes  dense  and  sometimes  porous, 
sometimes  very  fine  and  sometimes  coarse.  Small  particles  of  clay , 
little  shells,  and  various  other  substances  are  often  present.  The 
color  is  almost  invariably  black.  A  piece  heated  upon  a  stove 
quickly  falls  in  pieces,  if  it  contains  more  than  6  per  cent  of  asphalt. 
Asphaltic  sandstone  often  contains  considerable  quantities  of  maltha 
and  petroleum  which  injure  it  for  paving  purposes. 

586.  Chemical  Composition.  Asphalt  is  not  a  mineral  of 
definite  chemical  composition.  Generally,  it  is  a  compound  con- 
sisting of  various  hydro-carbpns,  which  can  be  separated  from  each 
other  only  with  great  difficulty.     Its  chemical  composition  when 


ART.  1.]  THE   ASPHALT.  389 

pure  is:  carbon,  80  to  88  per  cent;  oxygen,  0.5  to  10  per  cent; 
hydrogen,  9  to  11  per  cent;  nitrogen,  0  to  1  per  cent.  Asphalt  is 
often  found  mixed  with  other  minerals,  which  may  be  called  im- 
purities, the  most  common  of  these  being  sulphur,  which  sometimes 
constitutes  from  1  to  10  per  cent  of  the  whole.  Varieties  of  asphalt 
from  different  localities  seldom,  if  ever,  agree  with  each  other  in 
chemical  composition. 

Asphalt  may  be  separated,  with  more  or  less  readiness,  into 
several  different  substances  which  differ  somewhat  in  chemical 
composition  and  widely  in  physical  properties,  the  presence  or  ab- 
sence of  which  has  an  important  influence  on  the  value  of  the 
asphalt  for  paving  purposes.  The  principal  of  these  substances  are 
asphaltine,  petroline,  and  retine.  Under  the  head  of  asphaltine  has 
been  classed  that  part  of  the  asphalt  which  is  soluble  in  chloroform 
and  bisulphide  of  carbon,  and  not  in  ether  or  naphtha;  under  the 
head  of  petroline  has  been  classed  that  part  which  is  soluble  in  ether 
and  naphtha;  and  under  retine  has  been  classed  that  part  which  is 
soluble  in  alcohol.  Asphaltine  is  hard  and  brittle,  requires  a  high 
heat  to  melt  it,  or  burns  without  becoming  melted,  and  has  very 
little,  if  any,  of  the  adhesive  qualities  which  make  asphalt  useful  as  a 
cement.  Petroline  is  softer  than  asphaltine,  becomes  fluid  at  a 
lower  temperature,  has  great  adhesive  or  cementitious  qualities, 
and  is  the  valuable  part  of  asphalt  for  most  industrial  work.  Retine 
possesses  the  character  of  vegetable  resin,  and  is  not  considered  as 
adding  anything  to  the  value  of  asphalt  for  paving  purposes. 

It  is  very  questionable,  however,  whether  this  division  is  well 
founded.  Chemists  differ  widely  as  to  the  quantities  of  each  of 
these  so-called  elements  found  in  samples  from  the  same  locality, 
the  results  varying  with  the  details  of  the  methods  of  making  the 
determinations,  and  with  slight  variations  in  the  solvents  employed. 

Recently  investigators  are  inclined  to  class  all  the  components  of 
asphalt  under  two  heads  only,  the  active  and  the  inert.  The  active 
element  is  that  part  which  is  easily  melted  by  heat,  is  readily  solu- 
ble in  ether  or  naphtha,  and  is  highly  adhesive  and  cementitious; 
while  the  inert  material  is  the  hard  and  brittle  part  which  is  not 
readily  melted  by  heat,  and  which  adds  nothing  to  the  cementitious 
properties  of  the  asphalt.  The  ratio  in  which  the  active  and  the 
inert  constituents  are  combined  is  the  true  index  of  the  value  of  the 


390  ASPHALT   PAVEMENTS.  [CHAP.  XIII. 


asphalt  for  use  as  a  cement;  but  for  other  industrial  purposes,  such 
as  insulating  electric  wires,  etc.,  it  has  no  practical  value,  for  the 
active  and  the  inert  constituents  appear  to  be  equally  good  as  non- 
conductors. 

Asphalts  from  different  sources  should  not  be  compared  by  their 
chemical  analyses  unless  exactly  the  same  methods  and  solvents 
have  been  used  in  each  case.  Further,  it  has  been  found  that  the 
chemical  analysis  of  asphalt  is  not  a  reliable  indication  of  its  value 
as  a  cement,  since  asphalts  having  practically  the  same  composition 
differ  comparatively  widely  as  to  their  physical  properties. 

587.  PHYSICAL  PROPERTIES.  Crude  and  also  refined  asphalts 
from  different  localities  differ  widely  in  consistency,  in  susceptibility 
to  changes  of  temperature  and  to  changes  by  age,  in  stability  at  high 
temperatures,  cohesiveness,  adhesiveness,  elasticity,  etc.  Not  in- 
frequently data  are  given  to  prove  the  alleged  superiority  of  an 
asphalt  in  one  or  more  of  these  particulars;  but  there  is  no  recog- 
nized standard  for  testing  the  physical  properties  of  asphalt,  and 
the  results  of  such  tests  are  usually  stated  in  terms  so  general  as  to 
be  of  no  scientific  value.  For  example,  the  viscosity  at  different 
temperatures  is  stated  in  such  terms  as  "  compressible, "  "  easily 
bent,"  "malleable,"  "softens,"  "melts,"  "flows,"  etc.  The  results 
depend  upon  the  details  of  the  method  of  making  the  tests  and  upon 
the  degree  to  which  the  asphalt  has  been  refined;  and  as  a  rule 
such  tests  are  useless  except  perhaps  in  comparing  two  asphalts 
tested  at  the  same  time  under  the  same  conditions. 

Some  natural  asphalts  are  so  hard  and  brittle  that  before  being 
used  for  paving  purposes  they  must  be  softened  by  adding  some 
fluxing  material  or  solvent,  as  a  fluid  bitumen  or  residuum  of  petro- 
leum; and  the  physical  properties  of  the  mixture,  called  asphaltic 
cement,  are  usually  examined  very  carefully  to  determine  the  prob- 
able quality  of  the  resulting  pavement,  for  which  purpose  standard 
tests  have  been  devised.  For  the  method  of  making  such  tests  see 
§610. 

588.  ORIGIN  OF  ASPHALT.  Although  it  is  generally  conceded 
that  asphalt  is  the  oxidized  residue  of  petroleum,  and  that  petro- 
leum is  derived  from  vegetable  or  animal  substances,  there  is  a  con- 
siderable difference  of  opinion  as  to  its  ultimate  origin  and  as  to  the 
manner  in  which  its  production  has  gone  forward.     For  a  careful 


ART.   1  ] 


THE   ASPHALT. 


391 


consideration  of  the  several  theories,  see  the  Origin  and  Accumula- 
tion of  Petroleum  and  Natural  Gas.  by  Prof.  Edward  Orton,  in  Vol. 
VI,  Report  of  Geological  Survey  of  Ohio,  p.  60-100. 

589.  LOCATION  OF  MINES.  Asphalt  is  found  mixed  with  more 
or  less  earthy  and  vegetable  matter,  or  impregnating  limestone  or 
sandstone.  The  localities  where  it  is  found  are  shown  in  Table  39. 
"One  or  more  mines  are  worked  in  each  of  these  countries,  except, 
perhaps,  Columbia,  Indian  Territory,  Montana,  New  Mexico,  Mich- 
igan, Washington,  and  Dalmatia."  The  principal  sources  of  supply 
will  be  considered  separately. 

TABLE  39. 
Location  of  Asphalt  Deposits* 


Ref. 
No. 

Mixed  with  Earthy 
Matter. 

Impregnating  Limestone. 

Impregnating  Sandstone. 

1 

Bagdad 

Austria 

California 

2 

California 

California 

Colorado 

3 

Colorado 

Dalmatia 

Cuba 

4 

Columbia 

France 

France 

5 

Indian  Territory 

Germany 

Germany 

6 

Mexico 

Hungary 

Indian  Territory 

7 

Montana 

Indian  Territory 

Kentucky 

8 

Palestine 

New  Mexico 

New  Mexico 

9 

Peru 

Michigan 

Russia 

10 

Texas 

Italy 

Texas 

11 

Trinidad 

Russia 

Utah 

12 

Utah 

Sicily 
Spain 

13 

Venezuela 

14 

Switzerland 
Texas 
Utah 
Washington 

15 

16 

17 

590.  Trinidad  Asphalt.  The  Island  of  Trinidad  near  the  north- 
east coast  of  Venezuela,  South  America,  supplied  something  like 
90  per  cent  of  all  the  asphalt  used  in  the  world  from  about  1875 
to  1900.  At  present  the  Island  of  Trinidad  is  the  main  source  of 
supply  of  the  asphalt  used  in  the  United  States. 

The  island  contains  about  1,750  square  miles. f     Near  the  south- 

*  Natural  Asphaltum  and  its  Compounds,  by  J.  W.  Howard.  A  pamphlet  pub- 
lished by  Rensselaer  Society  of  Engineers,  Troy,  N.  Y..  1894. 

fFor  an  elaborate  description  of  the  island  and  of  the  asphaltic  products,  see 
the  Report  of  the  Inspector  of  Asphalt  and  Cements  of  Washington,  D.  C,  for  the 
year  1891-92,  pages  464-98  of  the  Report  of  the  Engineer  Commissioner  of  the  Dis- 
trict of  Columbia  for  1891-92. 


392  ASPHALT   PAVEMENTS.  [CHAP.   XIII. 

west  corner  is  the  so-called  pitch-lake,  which  has  an  area  of  about 
115  acres.  The  surface  of  the  lake  has  an  elevation  of  138  feet  above 
the  sea-level,  and  the  asphalt  has  a  depth  of  78  feet  near  the  center. 
The  surface  of  the  lake  has  a  slight  fall  from  the  center  toward  the 
sides,  and  a  general  inclination  toward  one  side,  and  is  covered  with 
irregular  flattened  domes,  separated  by  channels  of  flowing  water  a 
few  feet  wide  and  a  few  inches  deep.  There  are  several  islands  50 
to  60  feet  in  diameter  scattered  over  the  surface  of  the  lake,  which 
have  sufficient  depth  of  soil  to  support  the  growth  of  large  trees. 
The  surface  of  the  asphalt  is  sufficiently  hard  that  teams  may  be 
driven  over  it;  but  the  whole  mass  is  in  constant  motion  around 
several  vortices,  as  shown  by  trunks  of  trees  which  rise  and  after  a 
time  disappear  again.  Excavations  made  during  the  day  close  up 
during  the  night.  At  a  place  in  the  center,  called  the  boiling  spring, 
soft  pitch  wells  up,  but  soon  becomes  hard.  The  appearance  of 
boiling  is  due  to  the  escape  of  large  volumes  of  sulphuretted  hydro- 
gen. 

The  asphalt  is  excavated  with  picks  and  shovels,  conveyed  to 
the  shore  in  carts,  and  lightered  to  vessels  off-shore.  On  the  voyage 
it  becomes  compacted  into  a  solid  mass  and  must  be  again  broken 
up  with  picks.  The  crude  asphalt  is  mixed  with  much  earthy  and 
a  little  vegetable  matter  and  water  and  is  dark  brown,  brittle,  and 
as  dense  as  dry  peat. 

The  crude  material  is  refined  by  placing  it  in  kettles  or  open 
tanks  and  heating  it  for  three  or  four  days,  during  which  time  the 
water  is  evaporated,  the  vegetable  matter  rises  to  the  surface  and 
is  skimmed  off,  and  the  earthy  material  settles  to  the  bottom. 
Although  this  is  called  refining,  it  is  really  little  more  than  a  drying 
process,  since  but  little  mineral  matter  subsides,  and  only  the  water 
and  the  volatile  oils  are  driven  off.  The  mineral  matter,  if  inert 
and  insoluble  in  water,  is  not  detrimental  to  an  asphalt  for  paving 
purposes;  but  the  non-bituminous  organic  matter  and  the  soluble 
mineral  matter  are  prejudicial.  Great  care  is  required  in  the  refin- 
ing process  not  to  heat  the  asphalt  to  a  point  where  chemical  changes 
take  place.  The  refined  asphalt  must  be  Softened  by  the  addition 
of  some  fluxing  material  before  it  is  ready  for  use  in  the  pavement 
—see  §  604. 

591.  The  above  refers  to  asphalt  obtained  from  the  so-called 


ART.  1.] 


THE   ASPHALT. 


393 


lake ;  but  asphalt  is  also  mined  from  the  slopes  between  the  lake  and 
the  sea.  The  former  is  called  lake  asphalt,  and  the  latter  land  or 
overflow  asphalt,  or  less  frequently  iron  pitch.  Both  have  the 
same  origin,  the  land  asphalt  simply  being  asphalt  from  the  lake 
which  has  overflowed  the  surrounding  land.  The  land  asphalt, 
having  been  exposed  to  the  elements  for  a  longer  time  than  the  lake 
asphalt,  and  having  lost  part  of  its  volatile  oils  and  having  been 
partially  oxidized,  is  less  plastic  than  that  from  the  lake.  For  a 
number  of  years  there  was  a  sharp  commercial  controversy  as  to 
the  alleged  superiority  of  the  lake  asphalt;  but  at  present  the 
controversy  has  practically  subsided.  The  composition  of  neither 
is  uniform,  and  therefore  the  above  difference  is  not  of  much  im- 
portance, particularly  as  only  about  10  or  12  per  cent  of  the  asphalt 
mixture  in  the  pavement  is  asphalt.  The  average  composition  of 
the  three  grades  is  shown  in  Table  40. 

TABLE  40. 

Composition  of  Trinidad  Asphalt.* 


Ref.    I 

No.     I 


Components. 


Lake. 


Soft. 


Hard. 


Land, 


Crude  Material: 
Bitumen  soluble  in  carbon  bi 

sulphide 

Earthy  matter 

Vegetable  matter 

Water.. 

Total 

Refined  Material: 

Bitumen  soluble  in  carbon  bi- 
sulphide   

Earthy  matter 

Vegetable  matter 

Total 


34.50% 

25.05% 

6.35% 

34 .  10% 


38.14% 

26.38%, 
7.63% 

27.85% 


37.76% 

27.57% 

8.05% 

26.62%, 


100.00%      100.00%,      100.00%, 


52.36% 

38.00% 

9.64% 


100.00%, 


52.87% 
36.56%, 
10.57% 


51.58% 

37.74% 
10.68% 


100.00%      100.00% 


*  Compiled  from  Report  of  Engineer  Commissioner  of  District  of  Columbia  for 
1891-92,  pages  47G-77. 


592.  Bermudez  Asphalt.  This  is  the  name  given  to  the  asphalt 
obtained  from  a  lake  or  deposit  situated  in  the  state  of  Bermudez, 
Venezuela.     This  deposit  is  said  to  have  an  area  of  over  1,000  acres. 


394  ASPHALT   PAVEMENTS.  [CHAP.   X7  X 

It  is  situated  about  60  miles  from  the  coast,  up  the  San  Juan  river, 
and  about  51  miles  distant  from  it.  A  narrow-gage  steam  railroad 
connects  the  deposit  with  the  shipping  point,  so  that  vessels  draw- 
ing 18  feet  of  water  can  be  loaded  directly  from  the  cars. 

The  crude  asphalt  is  of  the  same  Variety  as  the  Trinidad, 
namely,  bitumen  mixed  with  sand,  clay,  and  vegetable  matter. 
The  average  composition  of  the  crude  material  is  about  as 
follows: 

Bitumen  soluble  in  carbon  bisulphide 93 .  54  per  cent 

Earthy  matter 2.16  " 

Vegetable  matter 1 .  15  " 

Water 3.15  "       " 

Total 100.00     M       " 

The  refining  process  is  similar  to  that  described  for  Trinidad  asphalt 
(§  590) ;  but  it  is  much  more  rapid,  owing  to  the  smaller  amount  of 
water  and  mineral  matter  present.  In  manufacturing  asphaltic 
cement,  the  Bermudez  asphalt  requires  much  less  of  the  fluxing 
agent  than  does  the  Trinidad  on  account  of  the  large  amount  of  oil 
contained  in  the  former. 

593.  California  Asphalt.  The  aborigines  of  California  used 
asphalt  for  making  their  canoes  water-tight  and  for  cementing  their 
utensils  and  weapons;  and  the  Spanish  Mission  fathers  who  first 
civilized  the  country  used  it  for  making  floors,  walks,  reservoirs, 
and  water  conduits.  The  Mexicans  who  settled  the  country  after 
the  establishment  of  the  missions  also  found  many  uses  for  the 
asphalt,  and  there  are  still  to  be  seen  numerous  examples  of  their 
cisterns,  pavements,  walks,  etc.,  in  a  good  state  of  preservation. 
These  uses  were  entirely  local;  and  no  steps  were  taken  to  extend 
the  applications  of  asphalt  until  in  1884  some  bituminous  sandstone 
was  shipped  from  Santa  Cruz.  In  recent  years  the  asphalt  industry 
of  the  state  has  reached  a  considerable  development;  and  at  present 
California  is  the  principal  producer  of  asphalt  in  the  United  States. 
Probably  this  state  not  only  has  larger  quantities  of  asphalt  than 
any  other  equal  area  in  the  world,  but  has  a  greater  variety  of  forms 
— solid  and  liquid  asphalt,  and  asphaltic  limestones  and  sandstones, 
— and  in  more  localities.  It  is  found  in  the  immediate  region  of 
the  Coast   Range,  from  Point  Arena   on  the  north  coast  to   Los 


ART.   1.]  THE   ASPHALT.  395 

Angeles  in  the  south,  but  chiefly  in  that  part  of  the  range  lying 
south  of  San  Francisco. 

Maltha  ("  fluid  bitumen  or  liquid  asphalt w)  is  found  in  small 
quantities  in  a  number  of  places  in  the  state,  but  the  deposit  of 
most  commercial  value  is  the  Las  Conchas  mine,  situated  at 
Carpinteria  in  Santa  Barbara  county,  about  13  miles  east  of  the 
city  of  Santa  Barbara,  on  the  shore  of  the  Pacific  Ocean.  The 
deposit  consists  of  a  large  body  of  bituminous  sand  covering  an 
area  of  about  75  acres  to  a  depth  of  25  feet.  The  maltha  is 
supposed  to  be  supplied  from  a  stratum  of  bituminous  shale  upon 
which  the  sand  rests.  The  sand  is  covered  with  from  6  to  8  feet  of 
surface  loam  which  is  washed  off  into  the  sea  by  a  12-inch  stream 
of  water  under  pressure  supplied  by  steam  pumps.  A  thin  layer  of 
clay  resting  directly  upon  the  sand  is  next  removed  with  spades. 
The  sand  is  then  loaded  into  cars  with  hot  spades,  and  is  drawn 
by  a  cable  up  an  inclined  way  to  the  refinery,  where  it  is  dumped 
into  a  mixer  consisting  of  a  steam-jacketed  cylinder  in  which  re- 
volving arms  break  up  the  lumps.  The  material  then  falls  into 
vats  of  boiling  water,  the  maltha  floats,  and  the  sand,  sinking  to  the 
bottom,  is  carried  away  by  mechanical  means.  The  maltha  flows 
from  the  surface  of  the  water  through  a  spout  to  a  tank  whence  it  is 
pumped  into  a  storage  tank  at  a  higher  elevation.  From  there  it 
runs  into  refining  kettles,  where  it  is  subjected  for  twenty-four 
hours  to  a  heat  which  beginning  at  100°  F.  is  gradually  raised  to 
240°  F.  This  process  removes  all  aqueous  vapors  and  volatile  oils, 
and  then  the  material  is  ready  for  use.  The  refined  product  con- 
tains an  average  of  98.26  per  cent  of  pure  bitumen,  and  1.74  per 
cent  of  mineral  matter.  This  mine  is  the  most  extensive  producer 
of  natural  fluid  bitumen,  or  " liquid  asphalt,"  in  the  world.  This 
liquid  is  much  used  for  fluxing  the  harder  asphalts. 

The  most  extensive  deposit  of  solid  asphalt  in  California  is  at 
La  Patera,  Santa  Barbara  county,  10  miles  west  of  Santa  Barbara 
immediately  on  the  sea-shore.  There  are  facilities  for  both  rail  and 
water  transportation.  The  deposit  covers  an  area  of  several  hun- 
dred acres,  and  the  material  is  mined  much  as  coal  is.  The  supply, 
as  in  the  case  of  the  maltha,  comes  up  from  below,  slowly  but  .con- 
tinuously. It  is  not  soft,  but  is  friable,  and  breaks  readily  under 
the  pick.     The  average  composition  of  the  asphalt  is  as  follows : 


396  ASPHALT    PAVEMENTS.  [CHAP.   XIII. 

Bitumen  soluble  in  bisulphide 59 .  15  per  cent. 

Earthy  material 39 .  75    "     " 

Vegetable  matter 1.10    "     " 

Total 100.00    "     " 

Asphaltic  limestone  and  sandstone  are  found  at  a  number  of 
places  in  California,  in  all  degrees  of  richness  and  consistency.  The 
principal  deposits  are  at  Santa  Cruz,  in  Santa  Cruz  county,  at  San 
Luis  Obispo,  in  the  county  of  the  same  name,  and  at  Kings  City,  in 
Monterey  county.  The  asphalt  is  extracted  from  the  stone  by 
heating  the  mass  in  a  tank  and  drawing  off  the  liquid  asphalt,  which 
is  shipped  to  various  parts  of  this  country  to  be  used  for  paving  pur- 
poses. 

The  base  of  the  Calif  ornia  petroleums  is  asphaltic,  as  distinguished 
from  the  paraffin  base  of  the  eastern  oils,  and  the  process  of  refining 
petroleum  leaves  the  asphalt  or  maltha  as  a  residue,  and  at  several 
places  asphalt  is  produced  from  the  crude  petroleum. 

594.  Other  American  Asphalts.  Asphalt  is  found  in  quantities 
of  considerable  commercial  importance  in  Utah,  Colorado,  Indian 
Territory,  Texas,  and  Kentucky.  For  a  detailed  account  of  the 
geological  occurrence  of  asphalt  in  these  states,  see  an  article  by 
George  H.  Eldridge  on  Asphalt  and  Bituminous  Rock  Deposits  in 
the  United  States,  in  Annual  Report  of  U.  S.  Geological  Survey  for 
1900-01,  pages  219-464. 

595.  European  Asphalts.  Asphalts  from  which  pavements  are 
made  are  found  in  Val  de  Travers,  Canton  of  Neuchatel,  Switzer- 
land; Seyssel,  Department  of  Ain,  France;  Vorwohle  and  Limmer, 
Germany;  and  Ragusa,  Sicily.  The  first  two  are  the  most  im- 
portant sources  of  supply.  Although  widely  distributed,  these 
asphalts  are  practically  of  the  same  nature,  as  shown  by  Table  41, 
page  397,  and  occur  in  strata  varying  in  thickness  from  6  to  23  feet. 
The  rock  is  quarried,  and  then  the  blocks  are  crushed  to  the  size  of  an 
egg  by  rollers  provided  with  teeth  and  revolving  at  different  speeds. 
These  pieces  are  next  reduced  to  a  powder  in  a  Carre  disintegrator, 
and  the  powder  is  sifted  to  uniform  fineness.  It  is  then  ready  for 
use  in  making  pavements.  Large  quantities  of  Trinidad  asphalt 
(§  590)  are  shipped  to  Europe  and  added  to  native  asphaltic  lime- 
stones deficient  in  asphalt.  On  the  other  hand,  asphalt  is  extracted 
from  European  asphalt  rocks  and  shipped,  usually  in  the  form  of 


ART.   2] 


SHEET    ASPHALT    PAVEMENTS. 


397 


cakes  weighing  50  to  60  pounds,  to  this  country  to  be  used  in  mak- 
ing artificial  paving  compounds. 

TABLE  41. 
Chemical  Composition  of  European  Asphaltic  Limestones. 


Pef. 

No. 

Components. 

Valde 
Travers.* 

Seyssel.* 

Limmer.     Vorwohle.f 

Sicilian.^ 

1 

o 

3 

4 

Bitumen  soluble  in  car- 
bon bisulphide 

Carbonate  of  lime 

Volatile  at  100°  C 

Miscellaneous 

10.10 

87.95 
0.50 
1.45 

8.00 

89.55 

1.90 

0.55 

1 

14.30           5.37 

67.00         90.80 

1.18           0.34 

17.52           3.49 

8.85 

87.50 
0.80 
2  85 

Total 

100.00 

100.00 

100.00        100.00 

1 

100  00 

*  Analysis  by  Laboratoire  de  l'Ecole  des  Pouts  et  Chaussees. 
f  Analysis  of  Sicilian  Paving  Co.,  New  York  City. 

Art.  2.     Sheet  Asphalt  Pavements. 

596.  A  sheet  or  monolithic  asphalt  pavement  consists  primarily 
of  (1)  a  wearing  coat  H  to  2  inches  thick  composed  of  asphaltic 
paving  cement  mixed  with  sand;  (2)  a  binder  course  composed  of 
broken  stone  and  asphalt  cement;  and  (3)  a  foundation  of  hydraulic 
cement  concrete  or  an  old  pavement  of  cobble  stones,  granite  blocks, 
bricks,  or  the  like.  Tn  this  country  when  the  term  asphalt  pavement 
is  used  the  above  form  is  usually  intended.  The  term  sheet  or  mono- 
lithic pavement  is  not  distinctive,  since  rock  asphalt  also  is  laid  as  a 
continuous  sheet;  but  no  confusion  is  likely  to  result,  since  in  this 
country  the  term  sheet  is  commonly  used  to  distinguish  the  mono- 
lithic form  from  the  asphalt  block  pavement,  and  since  in  Europe 
only  one  form  of  asphalt  pavement  is  used,  monolithic  natural 
rock.  In  contra-distinction  to  a  pavement  made  cf  natural  as- 
phaltic limestone  or  sandstone,  the  above  pavement  could  with 
some  propriety  be  called  an  artificial  asphalt  pavement,  or  the  wear- 
ing coat  could  with  still  more  propriety  be  called  an  artificial  asphal- 
tic paving  compound;  but  the  distinction  is  not  important  since 
the  sheet  asphalt  pavement  is  laid  almost  exclusively  in  this  country 
and  the  rock  asphalt  almost  exclusively  in  Europe. 

597.  HISTORICAL.  The  first  artificial  sheet  asphalt  pavement 
in  this  country  was  laid  in  Newark,  N.  J.,  in  front  of  the  city  hall  in 


398  ASPHALT    PAVEMENTS.  [CHAP.   XII  t. 

1870.  In  1873  a  small  piece  was  laid  on  Fifth  Avenue,  New  Yoik 
City,  opposite  the  Worth  Monument.  A  few  other  experimental 
sections  were  laid;  but  the  first  test  on  a  large  scale  was  in  1876  on 
Pennsylvania  Avenue  in  Washington,  D.  C.  Preceding  1882,  out- 
side of  Washington,  D.  C,  there  were  not  more  than  half  a  dozen 
streets  in  this  country  paved  with  any  form  of  asphalt;  but  since 
that  date,  asphalt  pavements  have  increased  rapidly,  and  now  hun- 
dreds of  miles  of  it  are  in  use  on  the  streets  of  American  cities.  The 
following  statistics  show  the  rapid  growth  of  this  industry:  In  this 
country  in  1880  there  were  300,000  square  yards  of  sheet  asphalt 
pavements;  in  1885,  1,800,000;  in  1890,  8,100,000;  in  1895, 
21,500,000;  in  1900,  38,000,000.*  In  Europe  in  1900  there  were 
only  about  3,000,000  square  yards  of  asphalt  pavements  of  all 
kinds. 

598.  THE  FOUNDATION.  Since  the  sheet-asphalt  wearing 
surface  has  no  power  in  itself  to  act  as  a  bridge,  it  is  essential  that 
it  be  placed  upon  a  firm  unyielding  foundation;  and  consequently 
it  is  nearly  always  placed  upon  a  bed  of  hydraulic  cement  concrete, 
prepared  as  described  in  Art.  2.  Chapter  IX,  page  367.  For  heavy 
city  traffic,  the  concrete  is  usually  six  inches  thick;  and  for  light 
traffic,  it  is  sometimes  only  4  inches  thick.  The  proper  thickness 
will  depend  upon  the  weight  of  the  traffic,  the  strength  of  the  con- 
crete, and  the  bearing  power  of  the  soil. 

Occasionally  the  asphalt  is  laid  upon  a  bituminous-cement  con- 
crete (§563).  The  chief  advantage  claimed  for  the  bituminous  con- 
crete is  that  the  asphalt  wearing-surface  adheres  more  firmly  to  it 
than  to  the  hydraulic  concrete,  and  thus  prevents  weather  cracks 
(§  654)  and  waves  (§  655).  An  additional  advantage  of  bituminous 
over  hydraulic  concrete  is  that  less  time  is  required  for  the  former  to 
set.  On  the  other  hand,  the  bituminous  concrete  is  weaker  and  less 
reliable,  and  usually  is  more  expensive.  Further,  in  repairing  the 
wearing  surface,  it  is  difficult  to  separate  the  top  coat  from  the 
bituminous  base  so  as  to  secure  a  uniform  smooth  surface.  Bitu- 
minous concrete  never  was  so  common  as  hydraulic-cement  con- 
crete for  a  foundation,  and  has  now  practically  been  abandoned. 
It  is  necessary  that  the  concrete  be  thoroughly  dry  before  the 

*  P.  W\  Henry,  Vice-President  and  General  Manager  of  Barber  Asphalt  Paving 
Co.,  in  Engineering  News,  Vol.  45,  p.  183. 


ART.  2.]  SHEET   ASPHALT   PAVEMENTS.  399 

asphalt  mixture  is  laid  upon  it,  as  the  generation  of  steam  caused 
by  placing  the  hot  material  upon  a  damp  foundation  will  produce 
blistering  and  possibly  disintegration  of  the  wearing  coat.  This  is  a 
matter  that  needs  close  attention  in  laying  an  asphalt  pavement. 
To  dry  the  foundation  after  a  rain  or  during  damp  weather,  fine  hot 
sand  is  sometimes  spread  over  the  concrete  and  then  swept  off;  but 
this  method  is  expensive  and  not  very  effective,  and  besides  there 
is  liability  that  enough  sand  will  be  left  upon  the  foundation  to 
interfere  with  the  adhesion  of  the  asphalt. 

599.  Often  an  old  pavement  of  broken  stone,  cobble  stones, 
granite  blocks,  or  brick  is  used  for  a  foundation  for  an  asphalt  pave- 
ment. All  of  these  give  fairly  good  results,  but  it  is  important  that 
the  surface  of  each  shall  be  perfectly  clean  and  dry  when  the  asphalt 
wearing  coat  is  laid. 

600.  BINDER  COURSE.  This  is  a  layer  about  1£  inches  thick 
of  broken  stone  cemented  together  with  asphaltic  paving  cement 
(§  603),  and  rolled  in  place  while  hot.  The  purpose  of  this  course 
is  to  bind  the  wearing  coat  and  the  foundation  or  base  together,  and 
to  prevent  the  wearing  coat  from  lifting  from  the  foundation  or 
from  being  pushed  along  in  a  wave. 

The  broken  stone  is  screened  to  pass  a  1-inch  or  a  lj-inch  mesh, 
and  after  being  heated  not  more  than  5  or  10  per  cent  should  pass 
a  No.  10  screen.  An  excess  of  fine  stone  is  undesirable,  since  more 
asphalt  is  required  to  coat  it,  and  also  since  the  coarser  stone  gives 
a  rougher  upper  surface  and  therefore  affords  a  better  anchorage 
for  the  top  course  of  the  pavement. 

The  apparatus  for  heating  the  stone  consists  of  a  revolving  steel 
cylinder  about  30  inches  in  diameter  and  12  to  14  feet  long,  set  at  a 
slight  inclination.  On  the  interior  are  deflectors  to  distribute  the 
stone  in  its  course  through  the  drum.  The  cylinder  is  heated  by 
means  of  either  wood  or  fuel-oil,  preferably  the  latter,  as  it  can  be 
more  closely  regulated.  The  broken  stone  to  be  heated  is  carried 
by  an  endless  chain  and  bucket  elevator  to  a  hopper  just  above  the 
cylinder  in  which  it  is  to  be  heated,  from  which  it  is  fed  into  the  heat- 
ing cylinder.  The  temperature  of  the  stone  as  delivered  from  the 
heater  is  controlled,  not  only  by  the  fire,  but  by  the  rate  at  which 
it  is  fed  into  the  heating  drum.  The  stone  should  leave  the  heat- 
ing drum  at  a  temperature  of  about  300°  F. 


400  ASPHALT    PAVEMENTS.  [CHAP.   XIII. 

The  hot  stone  is  fed  into  a  mixer  which  consists  of  an  inclined 
steel  cylinder  2\  to  3  feet  in  diameter  and  10  to  14  feet  long.  On 
the  axle  of  this  cylinder  are  blades  which  push  the  material  through 
the  drum  and  also  aid  in  mixing  the  stone  and  the  asphaltic  cement. 
When  the  mixing  is  well  regulated,  the  hot  stone  is  fed  into  the  upper 
end  of  the  mixer,  the  asphaltic  cement  at  a  temperature  of  300°  to 
325°  F.  is  poured  over  the  stone  in  proper  proportions  from  a  drip- 
ping tank,  and  the  binder  drops  continuously  out  of  the  lower  end 
of  the  mixer  into  a  cart.  Considerable  skill  is  required  in  regulating 
the  temperature  of  both  the  stone  and  the  cement,  and  in  adding 
the  proper  amount  of  the  latter. 

The  asphaltic  cement  is  the  same  as  that  used  for  the  wearing 
coat  (see  §  603),  except  that  it  is  mixed  much  softer.  The  asphalt 
for  the  wearing  coat  is  usually  mixed  to  a  consistency  represented 
by  a  penetration  of  35°  to  55°  with  the  Dow  needle  (§  613),  while 
the  cement  for  the  binder  course  has  a  penetration  of  70°  to  90°. 
This  cement  is  added  to  the  hot  stone  in  the  proportion  of  6  to  7 
pints  of  cement  to  1  cubic  foot  of  stone;  or  in  other  words,  the 
binder  is  mixed  so  as  to  contain  about  5  per  cent  of  bitumen  soluble 
in  carbon  bisulphide.  Each  fragment  of  stone  should  be  thoroughly 
coated  with  cement,  but  there  should  be  no  excess.  If  too  much 
cement  is  used,  it  either  drains  off  on  its  way  to  the  street,  or  is 
drawn  by  capillary  attraction  into  the  wearing  coat  and  causes  it  to 
disintegrate  (§  642).  If  too  little  cement  is  used,  the  fragments  of 
the  stone  will  not  adhere  firmly  together  and  the  whole  course  is 
liable  to  break  up  under  the  roller.  The  surface  of  the  coated  stone 
should  be  bright  and  glossy,  and  should  not  appear  dull  and  dead, 
a  condition  which  is  due  either  to  an  overheating  of  the  stone  or  to 
a  lack  of  cement. 

While  hot,  the  mixture  is  hauled  to  the  street,  distributed  uni- 
formly over  the  foundation,  and  rolled  until  it  is  cold,  the  founda- 
tion having  previously  been  made  clean  and  dry.  After  being  com- 
pacted, the  binder  course  should  have  a  thickness  of  about  1^  inches, 
and  should  firmly  adhere  to  the  foundation. 

601.  The  above  method  of  making  the  binder  course  is  the  one 
employed  at  Washington,  D.  C,  but  sometimes  a  practice  somewhat 
different  prevails.  The  stone  is  made  very  fine,  one  quarter  to  one 
half  of  an  inch  in  greatest  dimension,  and  the  cement  is  made  of 


ART.   2.]  SHEET   ASPHALT    PAVEMENTS.  401 

the  same  penetration  as  that  in'  use  in  the  wearing  surface.  The 
finer  stone  requires  more  asphalt  to  coat  it;  and  the  upper  surface 
is  smoother,  and  offers  less  resistance  to  the  pushing  of  the  top 
coat  into  waves.  Made  in  this  way  the  binder  is  a  dense  inelastic 
concrete,  and  lacks  the  essential  elements  of  a  good  binder.  The 
coarser  stone  and  the  softer  cement  are  preferable,  since  the  binder 
then  is  more  elastic  and  less  liable  to  damage  in  hauling  the  wear- 
ing coat  over  it,  and  gives  a  better  anchorage  to  the  wearing  coat. 
Formerly  coal  tar  was  used  as  the  cement  in  the  binder  course, 
but  it  has  nearly  been  abandoned,  owing  (1)  to  its  variability  and 

(2)  to  the  fact  that  it  must  be  used  at  a  lower  temperature  (about 
220°  instead  of  300°  to  325°),  and  consequently  chills  more  easily, 

(3)  to  the  fact  that  it  is  a  weak  cement,  and  therefore  is  more 
liable  to  damage  in  placing  the  top  course,  and  (4)  because  it  some- 
times contains  an  oil  which  being  absorbed  by  the  wearing  coat 
causes  the  asphalt  to  disintegrate. 

602.  CUSHION  COAT.  The  binder  course  is  occasionally 
entirely  omitted  owing  to  the  expense  necessary  for  maintaining 
separate  appliances  for  mixing  the  stone  and  the  asphalt  of  the 
binder  course.  In  this  case,  a  thin  course  of  material  of  the  same 
composition  as  the  wearing  coat  (§  625),  except  that  it  contains  a 
little  more  cement,  is  laid  instead  of  the  binder  course,  and  is  called 
a  cushion  coat.  The  cushion  coat  is  usually  from  h  to  1  inch  thick, 
and  being  richer  in  cement  adheres  more  firmly  to  the  foundation 
than  would  the  top  coat. 

603.  ASPHALTIC  CEMENT.  The  cementitious  element  of  the 
wearing  coat  consists  of  commercially  refined  asphalt  mixed  with 
a  softening  or  fluxing  agent.  The  asphalt  has  already  been  dis- 
cussed (see  Art.  1). 

604.  Softening  Agent.  Many  of  the  asphalts  are  so  hard  and 
brittle  that  before  being  used  for  paving  purposes,  it  is  necessary  to 
soften  them  by  the  admixture  of  oil  or  liquid  bitumen.  The  selec- 
tion of  the  proper  fluxing  agent  for  the  harder  asphalts  is  a  very  im- 
portant matter.  For  example,  refined  Trinidad  asphalt,  which 
consists  of  52  to  56  per  cent  pure  bitumen,  is  usually  mixed  with 
about  IS  pounds  of  fluxing  material  (petroleum  residuum)  per 
hundred  pounds  of  asphalt;  and  hence  the  bitumen  added  in  the 
fluxing  material  is  equal  to  about  one  third  of  that  originally  in  the 


402  ASPHALT    PAVEMENTS.  [CHAP.   XIIL. 

asphalt,  or  the  bitumen  added  in  the  softening  agent  is  equal  to 
about  one  fourth  of  that  in  the  finished  pavement. 

There  is  a  considerable  difference  of  opinion  as  to  the  value  of 
different  fluxing  agents,  and  the  selection  of  a  proper  flux  involves 
several  unsettled  chemical  problems. 

The  properties  required  of  an  asphaltic  flux  are:  1.  It  should 
contain  no  material  volatile  under  300°  F.,  as  otherwise  the  volatile 
matter  will  be  given  off  while  the  paving  cement  is  being  heated 
preparatory  to  its  being  mixed  with  the  sand  of  the  wearing  coat, 
and  consequently  the  asphalt  will  lose  its  cementing  power.  2.  The 
flux  should  be  as  fluid  as  possible  in  order  that  the  greatest  softening 
effect  may  be  produced  by  the  least  quantity,  as  ordinarily  the  flux- 
ing agent  is  comparatively  expensive.  3.  The  softening  agent 
should  be  chemically  stable  and  not  lose  its  fluidity  by  molecular 
change.  4.  The  fluxing  agent  should  dissolve  the  asphalt  and  not 
simply  form  a  mechanical  mixture  with  it.  The  asphalt  consists  of 
asphaltine  and  petroline  (§  586),  the  former  being  entirely  devoid  of 
cementing  power  and  the  latter  highly  cementitious;  and  therefore 
the  fluxing  agent  should  dissolve  the  asphaltine. 

There  are  two  general  classes  of  asphaltic  flux  in  common  use: 
(1)  petroleum  residuums  or  artificial  bituminous  fluxes,  and  (2) 
malthas  or  natural  bituminous  fluxes.  The  first  is  composed  of 
liquid  paraffins,  and  the  second  of  fluid  natural  bitumens  of  the  same 
nature  as  asphalt.  There  are  two  forms  of  each  in  more  or  less 
general  use.  There  are  therefore  four  fluxing  agents;  viz.:  (1) 
residuum  from  the  paraffin  petroleums  of  Pennsylvania;  (2)  a  spe- 
cially prepared  paraffin, — petroleum  residuum  known  as  Pittsburg 
flux;  (3)  residuum  from  the  asphaltic  petroleums  of  California;  and 
(4)  maltha.  Until  recent  years  the  first  was  the  only  fluxing  mate- 
rial in  use,  but  at  present  all  four  are  in  more  or  less  common  use. 

605.  Paraffin-Petroleum  Residuum.  "  The  best  [paraffin]  petro- 
leum residuum  is  a  heavy  thick  oil  at  70°  F.,  which  begins  to 
solidify  at  58°  F.,  and  becomes  solid  at  48°  F.,  the  solidification 
being  due  to  a  crystallization  of  a  portion  of  its  constituents.  At  a 
temperature  of  90°  F.  it  becomes  very  limpid.  It  is  very  non- 
adhesive  in  character;  and,  when  in  a  solid  condition  from  cold  or 
other  causes,  it  is  very  waxy  in  consistency  and  entirely  lacking  in 
cementing  properties.     It  gradually  loses  its  fluidity  with  age,  ap- 


ART.  2.]  SHEET  ASPHALT  PAVEMENTS.  403 

parently  by  the  separation  from  the  residuum  of  a  light  brown 
amorphous  solid."  *  Whether  or  not  petroleum  residuum  com- 
pletely dissolves  the  bitumen  of  asphalt  has  been  an  open  question 
for  several  years,  but  some  recent  experiments  f  seem  to  show 
that  it  does  not.  "Judging  from  the  physical  properties  of  this 
residuum  and  its  chemical  relations  to  asphalt  bitumen,  it  is  not 
a  desirable  flux."  t 

"The  best  petroleum  residuums  comply  with  the  following  tests: 
1.  The  specific  gravity  ranges  between  20°  and  23°  Baume.  2. 
The  flash  point  (as  taken  in  a  New  York  Board  of  Health  oil  tester) 
is  between  300°  and  425°  F.  3.  On  keeping  the  residuum  at  a 
temperature  of  400°  F.  for  thirty  hours,  it  must  lose  between  2  and 
6  per  cent  of  oil.  The  residue  in  the  retort  should  be  fluid  at  75°  F>, 
and  on  cooling  should  not  show  a  coarse  crystallization.  The 
quantity  of  residuum  necessary  to  soften  [Trinidad]  asphalt  into 
a  cement  containing  bitumen  whose  penetration  is  80°  (District  of 
Columbia  standard),  should  not  be  over  33  per  cent  of  the  total 
quantity  of  bitumen  in  the  asphalt.  4.  The  residuum  must 
show  only  the  slightest  signs  of  having  been  ' cracked'  [i.  e.,  that 
the  hydro-carbon  compounds  have  been  broken  up  into  new 
components  in  the  course  of  manufacture].  An  oil  that  has  been 
'cracked'  on  being  examined  through  the  microscope  reveals 
numerous  black  particles  floating  in  it.  The  particles  are  in^uble 
in  petroleum  naphtha,  but  are  soluble  in  carbon  bisulphide,  and 
resemble  asphaltine." 

606.  Pittsburg  Flux.  This  is  made  by  heating  paraffin-petro- 
leum residuum  with  sulphur,  which  favorably  changes  the  paraffin, 
and  has  been  used  to  a  limited  extent. 

607.  Asphalt-Petroleum  Residuum*  California  petroleum,  in 
asphalt  paving  literature  often  called  asphalt  oil,  is  an  excellent 
solvent  of  asphalt,  and  in  recent  years  has  been  much  used  as  a 
fluxing  material. 


*  A.  W.  Dow,  Inspector  of  Asphalts,  Washington,  D.  C,  in  Report  of  the  Opera- 
tions of  the  Engineering  Department  of  the  District  of  Columbia  for  the  year  ending 
June  30,  1898,  p.  124. 

\Ibid.,  p.  126. 

%  Ibid.,  1897,  p.  172. 


404  ASPHALT   PAVEMENTS.  [CHAP.   XIII. 

608.  Maltha.  This  is  a  liquid  bitumen  which  is  often,  but 
somewhat  improperly,  called  liquid  asphalt.  In  several  respects 
it  resembles  asphalt-petroleum  residuum;  but  in  other  particulars 
it  is  quite,  different.  It  is  unsuitable  for  use  as  a  fluxing  agent  fcr 
asphalt,  since  a  considerable  part  of  it^oy  some  authorities  *  esti- 
mated at  as  high  as  20  to  25  per  cent,  is  itself  asphalt  and  has  no 
fluxing  effect  upon  the  asphalt  to  which  it  is  added. 

609.  Mixing  the  Asphalt  and  the  Flux.  The  refined  asphalt  is 
brought  to  a  temperature  of  about  300°  F.,  and,  to  produce  rapidly 
a  uniform  mixture,  the  flux  also  is  heated  to  about  the  same  tem- 
perature. The  proper  amount  of  the  residuum  to  secure  an  asphal- 
tic cement  of  the  desired  consistency  (§  613)  is  then  added  to  the 
asphalt,  the  exact  amount  depending  upon  the  consistency  of  the 
asphalt  and  the  character  and  the  fluidity  of  the  flux.  Trinidad 
asphalt,  for  example,  requires  about  17  or  18  per  cent  of  paiaffm- 
petroleum  residuum.  After  adding  the  flux,  the  mixture  is  agitated 
for  several  hours  with  a  current  of  air  until  it  is  quite  homogeneous . 
This  agitation  must  be  done  with  great  thoroughness  to  insure  a 
uniform  cement,  and  must  be  continued  whenever  the  material  is  in 
a  melted  condition,  as  a  certain  amount  of  separation  takes  place 
when  the  melted  cement  stands  at  rest.  The  resulting  mixture  is 
known  as  asphaltic  cement;  and  if  the  mixing  has  been  well  done 
and^fre  proper  amount  of  suitable  flux  has  been  used,  the  cement 
is  ready  for  use  in  the  pavement. 

610.  Testing  the  Asphaltic  Cement.  To  determine  the  suita- 
bility of  the  asphaltic  cement  for  use  in  a  pavement,  it  is  necessary 
to  test  its  chemical  and  physical  properties.  The  chemical  test 
consists  in  the  determination  of  the  per  cent  (1)  of  bitumen. 
(2)  of  foreign  or  non-bituminous  organic  matter,  and  (3)  of  inorganic 
matter;  and  the  physical  tests  consist  in  determining  (1)  the  con- 
sistency or  the  softness  of  the  cement  and  its  susceptibility  to 
changes  of  temperature  and  to  changes  with  age,  (2)  the  stability 
of  the  cement  at  high  temperatures,  (3)  the  effect  of  water  and 
of  dilute  ammonia  upon  the  cement,  (4)  its  adhesiveness,  and  (5) 
its  cohesiveness. 

611.  Chemical  Composition.     The  per  cent  of  bitumen  maybe 

*  S.  F.  Peckham  in  Paving  and  Municipal  Engineering,  Vol.  7,  p.  171. 


ART.  2.]  SHEET   ASPHALT   PAVEMENTS.  405 

determined  in  various  ways,  but  is  most  easily  done  as  follows :  * 
"The  asphalt  is  spread  in  a  thin  layer  in  a  suitable  dish  (a  nickel  or 
an  iron  one  will  do),  and  kept  at  a  temperature  of  225°  F.  until  it 
practically  stops  losing  weight.  The  greater  part,  and  in  some 
cases  all,  of  the  water  and  some  light  oils  are  expelled  in  this  way. 
From  2  to  10  grams  (depending  upon  its  richness  in  bitumen)  of 
this  substance  is  weighed  in  a  large  tesjb  tube  (8  inches  long  by  1 
inch  diameter),  the  tare  of  which  has  been  previously  ascertained. 
The  tube  containing  the  substance  is  then  filled  to  within  1J  inches 
of  the  top  with  carbon  bisulphide  and  allowed  to  stand  for  a  few 
minutes.  Then  the  tube  is  tightly  corked  with  a  good  sound  cork, 
and  is  shaken  vigorously  until  no  asphalt  can  be  seen  adhering 
to  the  bottom.  Care  should  be  taken  while  shaking  to  keep  one 
finger  on  the  cork  to  prevent  its  being  blown  out.  The  tube  should 
then  be  put  away  in  an  upright  position  and  not  be  disturbed  in  the 
slightest  way  for  two  days,  after  which  the  carbon  bisulphide  is  de- 
canted off  into  a  small  bottle.  As  much  of  the  solvent  should  be 
poured  off  as  is  possible  before  losing  any  of  the  residue.  The  tube 
is  again  filled  and  shaken  as  before,  and  put  away  for  two  more  days. 
After  the  liquid  has  been  carefully  decanted  the  second  time,  the 
tube  with  the  residue  is  dried  first  at  a  low  temperature  and  then  at 
225°  F.  After  cooling  the  tube  is  weighed.  As  there  is  always  a 
small  portion  of  the  residue  poured  off  in  the  solution  with  the  bitu- 
men, this  solution  must  be  evaporated  and  the  bitumen  burned 
off  in  a  platinum  dish,  and  the  weight  of  the  residue  added  to  that 
in  the  tube." 

During  the  year  ending  June  30,1897,  the  per  cent  of  bitumen  in 
the  asphaltic  cement. used  in  Washington,  D.  C,  by  the  two  paving 
companies  doing  work  there  was  as  follows,  respectively:  average 
10.6  and  10.5,  maximum  12.6  and  12.7,  and  minimum  9.2  and  9.0. 

612.  "The  determination  of  the  organic  matter  not  bitumen,  or, 
as  it  is  often  called,  the  foreign  organic  matter,  is  made  by  burning, 
in  a  tared  platinum  crucible,  the  residue  left  in  the  tube  after  ex- 
tracting the  bitumen."  f 

*  A.  W.  Dow,  Inspector  of  Asphalts,  Washington,  D.  C,  in  Keport  of  the  Opera- 
tions of  the  Engineering  Department  of  the  District  of  Columbia  for  the  year  ending 
June  30,  1897,  p.  170. 

^  Ibid.,  p.  170. 


406  ASPHALT   PAVEMENTS.  [CHAP.   XIII.. 

613.  Standard  Consistency.  The  softness  or  the  consistency  of 
an  asphaltic  cement  is  determined  by  measuring  the  distance  a 
standard  needle  will  penetrate  the  mass  in  a  specified  time.  There 
are  two  forms  of  apparatus  in  use  for  this  purpose,  Bowen's  and 
Dow's. 

1.  Bowen's  Penetration  Apparatus.  This  apparatus  consists 
of  a  needle  of  standard  weight  and  size,  whose  vertical  motion  is 
registered  by  an  index  moving  over  a  graduated  disk.  This  is  ac- 
complished by  inserting  a  large  sewing  needle  in  the  free  end  of  a 
lever  arm  which  is  supported  by  a  thread  wound  around  a  spindle. 
The  spindle  carries  an  index  which  moves  over  a  graduated  disk. 
On  the  spindle  is  a  drum  round  which  winds  a  thread  supporting  a 
weight  which  acts  as  a  counterbalance  to  the  weight  of  the  lever 
arm.  This  counter-weight  keeps  the  thread  taut ;  and  when  the 
lever  arm  is  raised,  it  turns  the  pointer  on  the  dial.  The  penetra- 
tion of  a  sample  is  taken  by  lowering  the  needle  until  it  is  just  in 
contact  with  the  surface,  and  then  releasing  a  clamp  which  allows 
the  needle  to  penetrate  into  the  sample  for  a  specified  time — usually 
1  second.  At  the  end  of  the  time  the  clamp  is  closed,  and  the  de- 
gree of  penetration  is  noted  from  the  dial. 

The  sample  must  be  kept  at  a  standard  temperature,  usually 
77°  F.  (25°  C.)  for  at  least  half  an  hour  before  making  the  test.  This 
is  most  accurately  clone  by  keeping  the  machine  and  samples  in  a 
small  room  maintained  at  the  standard  temperature ;  but  is  usually 
done,  particularly  at  the  mixing  plant,  by  immersing  the  samples  in 
a  tank  of  water. 

Preceding  1899,  this  apparatus  was  the  standard  in  Washington, 
D.  C,  and  the  penetration  of  the  Trinidad  asphaltic  cement  used 
during  the  year  ending  June  30,  1897,  by  the  two  paving  companies 
doing  work  there  was  respectively:  average  77  and  85,  maximum 
83  and  100,  minimum  74  and  76. 

2.  Dow's  Penetration  Apparatus.  This  consists  of  an  ordinary 
No.  2  sewing  needle  fastened  into  the  end  of  a  small  brass  rod  which 
in  turn  is  fastened  into  tha  end  of  a  metal  tube  about  4  centimeters 
(1.6  inches)  long  and  1  centimeter  (0.4)  inch  in  diameter.  Mercury 
is  poured  into  the  tube  to  give  it  any  desired  weight  from  30  to  300 
grams.  The  brass  rod  and  the  tube  with  needle  end  down,  slides 
freely  up  or  down  through  a  frame,  and  can  be  held  in  any  position 


ART.  2.]  SHEET  ASPHALT  PAVEMENTS.  407 

by  a  clamp.  The  motion  of  the  sliding  part  is  communicated  by  a 
thread  to  an  index  arm  moving  over  a  graduated  disk.  The  test 
samples  are  kept  in  a  water- jacketed  copper  box,  which  rests  in  a 
tank  supplied  with  inlet  and  outlet  pipes  whereby  a  constant  tem- 
perature may  be  maintained.  The  apparatus  has  several  minor 
devices  to  facilitate  its  use  and  to  insure  accuracy.* 

The  unit  is  the  distance  in  hundredths  of  a  centimeter  that  a 
No.  2  needle  will  sink  into  an  asphalt  paving  cement  in  five  seconds 
when  weighted  with  100  grams,  the  cement  and  the  apparatus  being 
at  a  temperature  of  77°  F.  (25°  C).  The  penetration  can  be  meas- 
ured with  accuracy  to  one  fiftieth  of  a  millimeter  (0.000,8  inch). 
This  instrument  is  a  later  invention  and  is  claimed  to  be  more  ac- 
curate than  the  Bowen  apparatus.  Since  Jan.  1,  1.899,  this  instru- 
ment has  been  the  standard  in  Washington,  D.  C,  and  the  average 
penetration  of  the  Trinidad  asphalt  cement  used  by  the  two  com- 
panies doing  the  work  in  that  city  during  the  year  ending  June  30, 
1899,  was  36  and  45.  In  a  rough  way  the  unit  of  this  apparatus  is 
about  twice  that  of  the  Bowen  machine. 

614.  The  proper  softness  or  viscosity  of  the  asphaltic  cement 
depends  upon  the  kind  and  the  amount  of  the  traffic,  the  range  of 
atmospheric  temperature,  the  character  of  the  sand  used  (§  621), 
and  the  susceptibility  of  the  bitumen  to  changes  of  temperature 
(§  615)  and  to  changes  with  age  (§  616).  No  general  standards 
have  been  established,  and  but  little  accurate  information  is  known 
to  the  public  concerning  the  experience  in  any  city  except  Washing- 
ton, D.  C.  The  degree  of  penetration  employed  in  that  city  with 
both  the  Bowen  and  the  Dow  apparatus  is  stated  in  the  preced- 
ing section. 

615.  Variation  of  Consistency  with  Change  of  Temperature.  The 
susceptibility  of  the  paving  cement  to  changes  in  temperature  is 
determined  by  taking  the  penetration  of  the  substance  at  several 
different  temperatures  and  noting  the  variation  caused  by  the  rise 
or  fall.  The  chief  cause  of  the  Susceptibility  to  changes  in  tem- 
perature is  the  presence  of  the  paraffin  added  in  the  fluxing  agent. 
Paraffin  at  ordinary  temperatures  is  an  inert  solid;  but  as  soon  as 
heated  to  the  melting  point  it  quickly  liquefies,  and  then  acts  as  so 

*  Report  of  Operations  of  Engineering  Department  of  District  of  Columbia  for 
the  year  ending  1898,  p.  128-29. 


408  ASPHALT    PAVEMENTS.  [CHAP.    XTIT. 

much  additional  flux,  thus  suddenly  changing  the  consistency  of 
the  asphaltic  cement. 

616.  Variation  of  Consistency  with  Age.  "  All  bitumens  undergo 
a  more  or  less  rapid  change  with  aging,  a  fact  which  appears  to  be 
due  to  two  or  possibly  more  causes.  Two  distinct  changes  manifest 
themselves.  1.  A  surface  hardening  takes  place,  probably  due  to 
indirect  oxidation,  and  possibly  to  the  volatilization  of  the  light  oils. 
It  begins  at  the  surface  and  gradually  extends  into  the  mass.  2. 
A  hardening  of  the  entire  mass  takes  place,  evidently  due  to  poly- 
merization, i.  e.,  to  new  atomic  arrangement.  Both  of  these  changes 
take  place  in  all  bitumens,  but  one  or  the  other  may  predominate. 

"The  test  is  made  as  follows:  The  penetration  of  the  sample  is 
determined,  after  which  it  is  put  away  for  a  week,  when  the  penetra- 
tion is  again  ascertained.  If  the  sample  is  found  to  have  appreciably 
hardened,  a  slanting  cut  is  made  into  it  with  a  keen,  sharp  knife, 
thus  exposing  a  gradual  descent  from  the  surface  into  the  interior  of 
the  cement.  Penetrations  are  now  taken  down  the  side  of  this  cut, 
beginning  at  the  surface.  In  this  way  the  increase  in  hardness  of 
the  surface,  and  also  of  the  interior,  over  the  original  consistency  is 
determined.  It  is  well  to  continue  this  test  for  as  long  a  period 
as  possible,  making  examinations  at  intervals  of  every  few 
weeks. "  * 

617.  Stability  at  High  Temperature.  The  asphalt  must  remain 
at  a  high  temperature  for  a  considerable  time  in  mixing  it  with  the 
softening  agent  as  well  as  in  mixing  the  cement  and  the  sand;  and 
it  is  important  that  the  asphalt  mixture  shall  in  this  process  lose 
none  of  its  valuable  properties.  Owing  to  the  great  area  exposed 
to  evaporation  the  effect  of  high  temperature  is  especially  severe 
after  the  cement  has  been  mixed  with  the  sand.  The  lack  of 
stability  resulting  from  the  loss  of  the  light  oils  is  manifested  in 
different  ways  in  different  bitumens.  Although  generally  true,  it 
does  not  of  necessity  follow  that  the  bitumen  losing  the  most  oil 
undergoes  the  greatest  change  in  consistency.  There  are  two 
methods  of  making  this  test,  both  of  which  should  be  used : 

1 .  "  The  asphalt  cement  is  mixed  with  standard  sand  in  such 
proportions  that  the  mixture  will  contain  10  per  cent  of  bitumen. 

*A.  W.  Dow,  Inspector  of  Asphalts,  Washington,  D.  C,  Annual  Beport,  1897, 
p.  171. 


ART.  2.]  SHEET  ASPHALT  PAVEMENTS.  409 

This  is  done  by  keeping  the  ingredients  in  an  oven  for  15  minutes 
at  300°  F.,  and  then  incorporating  them  by  stirring.  One  portion 
of  this  mixture  is  then  put  aside  to  cool,  while  the  other  is  kept  at 
the  temperature  of  300°  F.  for  a  half  hour  longer.  The  bitumen  is 
then  extracted  from  both;  and  after  having  arrived  at  the  same 
temperature,  their  penetrations  are  compared. 

2.  "The  second  method  consists  in  keeping  a  quantity  of  the 
substance,  equivalent  to  20  grams  of  bitumen,  at  the  tempera- 
ture of  400°  F.  for  thirty  hours.  The  method  of  procedure  is  as 
follows:  The  substance  is  weighed  in  a  short-necked,  tubulated,  2- 
ounce  retort,  the  tare  of  which  has  been  previously  taken.  The 
retort  is  then  hung  in  a  copper  cylinder  so  that  the  neck  just  pro- 
trudes. The  copper  cylinder  is  then  jacketed  with  asbestos  and 
provided  with  a  thermometer.  After  being  heated  up  to  400°  F. 
for  thirty  hours,  the  retort  is  allowed  to  cool,  and  is  then  weighed. 
The  per  cent  of  loss  should  not  be  more  than  8  per  cent.  The  retort 
is  then  broken  open  and  the  character  of  its  contents  compared 
with  that  of  the  original  substance.' '  * 

618.  Effect  of  Water  and  Ammonia.  "  The  action  of  water  and 
dilute  ammonia  on  an  asphalt  mixture  is  determined  by  molding  an 
inch  cube  of  the  mixture  under  a  pressure  of  1,000  pounds.  The 
cube  is  broken  in  two,  one  portion  being  plaoed  in  water  or  dilute 
ammonia,  while  the  other  portion  is  kept  in  the  air.  The  two 
pieces  are  compared  from  time  to  time.  If  the  piece  has  been  acted 
upon  by  the  liquid,  the  corners  will  be  found  to  give  away  readily 
with  a  slight  pressure  of  the  finger.  After  soaking  some  time,  it  is 
well  to  evaporate  the  liquid  to  dryness  and  to  note  if  any  bitumi- 
nous residue  remains."  * 

619.  Adhesiveness.  Formerly  the  adhesiveness  of  asphaltic 
cement  was  supposed  to  be  measured  by  the  proportion  of  petroline 
(bitumen  soluble  in  ether  or  naphtha)  it  contained;  but  the  results 
differ  so  widely  with  different  asphalts,  with  variations  in  the  details 
of  making  the  experiments,  and  with  the  purity  of  the  solvents,  that 
the  test  has  been  practically  abandoned. 

The  adhesiveness  has  been  tested  in  a  few  cases  by  cementing 
together  with  asphalt  the  ends  of  hydraulic  cement  briquettes  an  I 

*  A.  W.  Dow,  Operations  Engineering  Department  of  District  of  Columbia  for 
1897,  p.  171. 


410  ASPHALT    PAVEMENTS.  [CHAP.   XIII. 

then  pulling  them  apart  with  a  cement-testing  machine.  Brass 
briquettes  have  been  used  instead  of  the  cement  ones,  the  surface 
to  which  the  asphalt  is  applied  being  left  rough.  When  using  these 
briquettes,  they  are  heated  in  water  to  about  140°  F.,  taken  out  and 
dried,  and  the  separate  ends  dipped  into  the  molten  asphalt.  The 
two  ends  of  the  briquette  are  then  pressed  together  and  allowed  to 
cool,  after  which  they  are  tested  in  the  same  manner  as  are  hydraulic 
cement  briquettes. 

At  present  the  only  test  in  general  use  is  to  compare  different 
asphalts  for  adhesiveness  by  the  sense  of  touch. 

620.  Cohesion.  Attempts  have  been  made  to  determine  the 
tensile  and  the  compressive  strength  of  asphaltic  cement,  by  much 
the  same  methods  as  those  employed  in  testing  hydraulic  cement, 
but  owing  to  difficulties  in  making  the  tests  the  practice  has  not 
been  generally  adopted.  The  strength  of  asphaltic  cement  varies 
materially  with  the  temperature,  and  flows  perceptibly  at  ordinary 
atmospheric  temperatures ;  and  therefore  the  details  of  the  experi- 
ments materially  affect  the  results.* 

621.  THE  SAND.  The  asphaltic  cement  is  mixed  with  inert 
mineral  matter,  mainly  sand,  to  form  the  wearing  coat.  The  min- 
eral matter  constitutes  about  90  per  cent  of  the  wearing  coat,  and 
its  character  and  composition  has  an  important  effect  upon  the 
quantity  and  durability  of  the  pavement. 

The  sand  should  be  (1)  clean  and  (2)  sharp,  and  (3)  be  composed 
of  grains  not  easily  crushed,  and  (4)  have  as  small  a  proportion  of 
voids  as  possible.  1.  It  should  be  free  from  clay,  loam  or  vege- 
table matter,  because  these  substances  are  devoid  of  cementing 
power,  are  easily  reduced  to  powder,  and  will  prevent  the  cement 
from  adhering  to  the  sand  grains.  2.  The  sand  should  have  sharp 
angular  grains  rather  than  smooth  round  ones,  since  the  former 
afford  a  better  surface  for  the  adhesion  of  the  asphaltic  cement,  and 
since  sand  with  angular  grains  is  much  less  mobile  and  hence  is 
more  easily  cemented  into  a  solid  mass  which  will  not  flow  under 
traffic.     3.  The  sand  grains  should  not  be  easily  crushed  by  the 

*  For  numerical  results  of  the  tensile  and  compressive  strength  of  three  asphalts, 
see  Jour.  Assoc.  Eng'g  Societies,  Vol.  13,  p.  492.  For  comparative  results  of  the 
ductility  of  seven  asphaltic  cements,  see  Proc.  Amer.  Soc.  of  Municipal  Improve- 
ments, Vol.  6,  p.  150-51. 


ART.  2.]  SHEET   ASPHALT   PAVEMENTS.  411 

traffic,  for,  if  they  are  broken  after  the  pavement  is  laid,  numerous 
surfaces  will  be  produced  which  are  not  coated  with  cement,  and  to 
that  extent  the  pavement  will  be  weakened.  4.  The  sand  should 
contain  as  small  proportion  of  voids  as  possible,  since  less  asphaltic 
cement  will  then  be  required. 

622.  The  ideal  condition  is  that  each  grain  shall  be  coated  and 
all  interstices  between  the  grains  be  filled  with  asphaltic  cement,  and 
hence  the  smaller  the  proportion  of  voids  the  less  the  cement  re- 
quired. Again,  the  asphaltic  cement  is  more  or  less  of  a  liquid 
having  capillary  action  between  the  sand  grains,  and  therefore  the 
smaller  the  interstices  between  'the  grains  the  greater  the  force  of 
attraction  between  the  liquid  cement  and  the  sand.  An  example 
of  the  adhesive  force  of  a  limpid  liquid  is  seen  in  a  sand  beach  when 
the  tide  has  just  left  it.  The  water  holds  the  sand  grains  so  firmly 
that  a  wagon  can  be  driven  over  the  sand  without  leaving  a  mark; 
but  when  the  sand  dries  out,  it  becomes  loose  and  mobile.  This 
seems  to  indicate  that  the  finer  the  sand  the  better;  but  fine  sand  is 
usually  less  sharp  than  coarse,  and  the  finer  the  sand  the  greater  the 
surface  to  be  coated,  and  hence  the  greater  the  amount  of  asphalt 
required.  The  asphalt  is  not  only  more  expensive  than  the  sand, 
but  it  is  less  able  to  resist  displacement  by  pressure;  and  conse- 
quently the  greater  the  amount  of  asphalt  present  the  more  expen- 
sive the  pavement,  and  the  more  liable  it  is  to  flow  under  traffic. 
On  the  other  hand,  the  smaller  the  voids,  the  greater  the  binding 
action  of  the  cement;  and  also  the  finer  the  sand  the  smaller  the 
voids,  although  the  per  cent  of  voids  may  be  greater  than  with  sand 
having  grains  of  graded  sizes. 

As  far  as  is  known,  no  experiments  have  been  made  to  determine 
the  relative  value  of  different  sands  for  asphalt  pavements;  but 
apparently  the  best  sand  is  that  in  which  the  coarse  and  fine  grains 
are  so  adjusted  that  the  finer  grains  fill  the  voids  between  the 
coarser  ones.  To  secure  this  condition,  it  has  been  the  custom  to 
mix  a  certain  amount  of  pulverized  limestone  with  the  sand.  The 
limestone  dust  is  used  to  fill  the  voids  between  the  coarse  sand 
grains,  and  thus  to  secure  at  once  a  minimum  surface  to  be  coated, 
the  smallest  interstices,  and  the  least  per  cent  of  voids. 

The  proper  proportion  of  pulverized  limestone  depends  upon  the 
fineness  of  the  limestone  and  of  the  sand;  and  the  best  proportion, 


412  ASPHALT   PAVEMENTS.  [CHAP.  XIII. 

i.  e.,  the  one  having  the  smallest  per  cent  of  voids,  in  any  particular 
case  can  be  determined  only  by  trial.  To  do  this,  thoroughly  mix 
the  sand  and  the  limestone  dust  in  some  definite  proportion  and 
then  determine  the  per  cent  of  voids  in  the  mixture.  To  determine 
the  voids,  procure  a  deep  and  rather  narrow  vessel,  say  a  tin  pail, 
and  find  the  weight  of  water  required  to  fill  it.  Next  fill  the  pail 
with  the  mixture  of  sand  and  limestone ;  and  then  slowly  pour  in  all 
the  water  the  pail  will  hold.  The  weight  of  water  required  to  fill 
the  pail  containing  the  sand  and  limestone  dust  divided  by  the 
weight  of  water  required  to  fill  the  empty  pail  is  the  per  cent  of 
voids  in  the  mixture  of  sand  and  limestone  dust. 

The  above  method  of  finding  the  voids  is  subject  to  a  consider- 
able error,  since  the  water  will  not  expel  the  air  from  the  sand ;  and 
therefore  it  is  better  to  consider  the  above  only  preliminary,  and 
proceed  as  follows:  The  sand  being  dry,  fill  the  pail  with  the  mix- 
ture, tamping  it  as  it  is  put  in ;  and  then  empty  the  pail  upon  a  table, 
taking  care  not  to  lose  any  of  the  material.  Next  put  into  the  pail 
a  little  less  water  than  is  required  to  fill  the  voids,  and  then  grad- 
ually pour  in  the  mixture  previously  emptied  upon  the  table,  tamp- 
ing it  as  it  is  added.  If  necessary  to  keep  the  mixture  wet,  add  a 
little  more  water  as  the  tamping  proceeds;  and  when  the  material 
is  all  in,  add  water  until  the  pail  is  level  full.  Then  the  total 
weight  of  water  in  the  mixture  divided  by  the  weight  of  water  re- 
quired to  fill  the  empty  pail  is  the  per  cent  of  voids  in  the  rammed 
mixture. 

The  amount  of  limestone  dust  ordinarily  used  varies  from  5  to  15 
per  cent  of  the  sand  (see  §  625) ;  and  the  fineness  is  usually  such 
that  all  will  pass  a  sieve  having  30  meshes  per  linear  inch  and  at 
least  75  per  cent  will  pass  a  sieve  having  100  meshes  per  linear  inch. 

Table  42,  page  413,  shows  the  average  fineness  of  the  sand  and 
limestone  dust  used  in  the  asphalt  pavements  laid  in  Washington 
City  by  the  two  paving  contractors  doing  work  there,  during  the 
year  ending  June  30,  1897,  and  also  the  fineness  recommended  by 
Mr.  A.  W.  Dow,  Inspector  of  Asphalt.  When  available,  other 
asphalt  paving  contractors  use  sand  and  limestone  dust  of  substan  - 
tially  the  fineness  stated  in  Table  42. 

623.  To  illustrate  the  relation  between  the  fineness  of  the  min- 
eral matter  and  the  softness  of  the  asphaltic  cement,  Mr.  Dow  cites 


ART.  2.] 


SHEET   ASPHALT    PAVEMENTS. 


413 


TABLE  42. 
Fineness  of  the  Mineral  Matter  Used  in  the  Wearing  Coat  of  As- 
phalt Pavements  in  Washington,  D.  C* 


6 

o 

1° 

T5 
Ii 

"8 

Size  of  Mesh. 

fin 

si 

1 

Retained 

on  10-meshper 

linear  inch 

0.0% 

o.o% 

0.0% 

2 

a 

u    20     "       " 

«        u 

0.017 

2.5" 

3.5" 

12.0" 

3 

ti 

«    40     t*       u 

a          a 

0.010 

24.5  " 

27.0  " 

25.0" 

4 

a 

"    60     "       " 

a          a 

0.007 

31.0" 

31.5" 

20.0" 

5 

It 

u     8Q       U         it 

a          a 

0.005 

16.0" 

15.0" 

10.0" 

6 

a 

"  100     "       " 

a          a 

0.004 

11,0" 

10.0" 

18.0" 

7 

Passed 

100     "      w 

a          a 

15.0" 

13.0" 

15,0" 

100.0  " 

100.0" 

100.0" 

the  following  examples :  f  The  fineness  of  the  sand  in  the  asphalt 
pavements  laid  in  Washington  in  1894  and  1897  was  as  below: 

Pavements  Laid  in 

1894.  1897. 

Retained  on    20-mesh  sieve 4 . 5%  2 . 5% 

"        "     40     "        "     40.0"  21.0" 

"     60     "        " 32.0"  35.0" 

<•     "'80     "        "     9.5"  8.5" 

"        "100     "        "     6.0"  10.0" 

Passed            100     "        " 8.0"  24.0" 

Total 100.0  "  100.0  " 

It  will  be  noticed  that  the  sand  used  in  1894  was  considerably 
coarser  than  that  employed  in  1897.  The  asphaltic  cement  used 
in  1894  was  20°  of  penetration  (Bowen  apparatus)  harder  than  that 
employed  in  1897;  but  nevertheless  the  1894  pavements  were  as  soft, 
and  in  some  cases  softer,  than  the  1897  pavements,  as  indicated  by 
the  tracks  left  by  the  traffic. 

The  Neuchatel  rock  asphalt  (§  595)  is  much  used  in  Europe,  and 
has  been  found  to  make  a  hard  and  durable  pavement.  This  so- 
called  rock  asphalt  is  a  limestone  powder  cemented  together  by  an 

♦Report  of  the  Operations  of  the  Engineering  Department  of  the  District  of 
Columbia  for  the  year  ending  June  30,  1897,  p.  167  and  169. 

f  Proc.  Amer.  Soc.  of  Municipal  Improvements,  Vol.  5,  p.  148. 


414  ASPHALT   PAVEMENTS.  [CHAP.  XIII, 

asphalt  "so  soft  that  its  flow  is  perceptible  at  a  temperature  of 
75°  F.,  which  is  about  three  times  softer  than  any  asphaltic  cement 
used  in  the  Washington  pavements." 

624.  All  asphaltic  cements  grow  harder  with  age,  and  are  likely 
to  crack  in  cold  weather;  and  therefore  it  is  desirable  to  use  as  soft 
a  cement  as  possible,  a  condition  which  seems  to  indicate  that  the 
sand  should  be  fine.  A  fine  smooth  sand  requires  a  considerably 
harder  cement  than  a  sharp  angular  sand.  If  the  cement  is  soft 
and  there  is  a  large  per  cent  of  voids  in  the  sand,  there  is  a  liability 
that  in  hot  weather  the  sand  will  work  to  the  bottom  and  the  asphalt 
to  the  top,  wheie  it  will  chip  and  scale  off  during  cold  weather. 

625.  THE  WEARING  COAT.  The  asphaltic  cement  and  the  sand 
(or  more  properly,  the  mineral  matter)  are  mixed  to  form  the  wear- 
ing coat.  Enough  cement  should  be  used  to  fill  the  voids  in  the 
compacted  sand,  as  otherwise  the  mineral  matter  will  not  be  held 
together  with  the  maximum  force;  but  more  cement  than  enough 
to  fill  the  voids  is  objectionable,  since  the  expense  is  increased,  an 
excess  of  asphalt  causes  the  wealing  coat  to  flow  under  traffic  during 
warm  weather,  and  also  causes  the  surface  to  chip  and  flake  off 
during  cold  weather. 

In  a  sense,  the  purity  of  the  asphalt  is  not  a  matter  of  impor- 
tance, since  the  more  mineral  matter  in  the  asphalt  the  less  the 
amount  of  sand  and  pulverized  limestone  required.  The  mineral 
matter  in  the  asphalt  is  usually  an  impalpable  powder  and  is  thor- 
oughly incorporated  with  the  bitumen;  and  therefore  it  is  more 
desirable  than  new  material.  However,  since  different  asphalts 
differ  materially  in  the  amount  of  contained  mineral  matter,  it  is 
customary  to  specify  the  amount  of  bitumen  soluble  in  carbon  bisul- 
phide which  the  completed  pavement  shall  contain.  In  southern 
cities  having  long  hot  summers,  the  soluble  bitumen  is  usually 
limited  to  from  9  to  12  per  cent;  and  in  northern  cities  to  from  12 
to  15  per  cent.  The  exact  quantity  varies  with  the  amount  and 
character  of  the  traffic,  the  climate,  the  fineness  of  the  mineral 
matter,  etc. 

Formerly  it  was  customary  to  state  the  composition  of  the 
wearing  surface  about  as  follows:  asphaltic  cement,  from  12  to  15 
per  cent;  sand,  from  70  to  83  per  cent;  limestone  dust,  from  3  to  15 
per  cent.    The  proportions  differ  considerably  with  the  locality,  the 


ART.  2.]  SHEET   ASPHALT   PAVEMENTS.  415 

contractor,  and  the  kind  of  asphalt  used.  The  method  of  stating 
the  composition  in  terms  of  the  per  cent  of  bitumen  is  more  exact, 
and  is  the  form  now  generally  employed. 

626.  The  proportions  of  the  wearing  coat  are  usually  stated  by 
weight,  while  the  method  of  finding  the  per  cent  of  voids  given  in 
§  622  determines  the  voids  in  volumes.  To  determine  the  propor- 
tions by  weight  proceed  as  follows:  Assume,  for  example,  that  it 
has  been  found,  as  described  in  §  622,  that  the  voids  in  a  mixture 
consisting  of  50  pounds  of  sand  and  5  pounds  of  limestone  dust 
contain  6  pounds  of  water;  and  assume  further  that  the  specific 
gravity  of  the  asphaltic  cement  is  1.25.  The  weight  of  the  cement 
required  to  fill  the  voids  in  the  above  quantity  of  sand  and  dust 
then  is  6  X  1.25  =  7.5  pounds.  The  proper  proportions  by  weight 
then  are : 

w«;<rht  Proportion  in 

I-edieut,                                    *£&-  &%&. 

Sand 50  80 

Pulverized  limestone 5  8 

Asphaltic  cement 1\  12 

Total 62£  100 

627.  Mixing  the  Cement  and  Sand.  The  asphaltic  cement  and 
the  sand  (or  rather  the  sand  and  the  limestone  dust  thoroughly 
mixed)  are  separately  heated  to  275°  to  325°  F.  The  proper  amount 
of  cement  and  sand  (§  626)  are  weighed  out  and  simultaneously 
poured  into  a  mechanical  mixer  consisting  of  two  sets  of  interlocking 
revolving  blades  which  thoroughly  mix  the  materials.  Usually 
about  800  pounds  of  cement  and  sand  are  mixed  in  one  batch.  When 
the  mixing  is  completed,  a  process  which  ordinarily  requires  at  least 
1  to  1$  minutes,  sliding  doors  in  the  bottom  of  the  mixer  are  opened, 
and  the  material  drops  out  into  the  carts  or  wagons  which  carry  it  to 
the  street.  In  this  condition,  it  is  a  loose  pulverulent  mass,  each 
grain  of  sand  being  very  completely  coated  with  the  asphaltic 
cement. 

Usually  the  temperature  of  each  load  is  taken,  and  a  canvas  is 
thrown  over  it.  The  operation  of  mixing  the  cement  and  sand 
requires  care  (1)  in  heating  the  ingredients  to  secure  a  uniform 
temperature  and  not  to  overheat  the  asphalt,  (2)  to  proportion 
the  mixture  accurately,  and  (3)  to  mix  the  materials  thoroughly. 


M6  ASPHALT    PAVEMENTS.  [CHAP.   X1IL, 

628.  There  is  no  accurate  method  of  determining  whether  the 
asphaltic  cement  and  the  mineral  matter  have  been  mixed  in  the 
best  proportions.  The  only  method  in  use  for  this  purpose  con- 
sists in  compressing  a  sample  of  the  hot  mixture  by  hand  between 
two  sheets  of  manilla  paper  or  smooth  brown  wrapping  paper,  and 
in  noting  the  mark  left  on  the  paper.  If  the  mixture  is  too  rich,  the 
Stain  will  be  distinct  and  blotchy,  and  some  of  the  cement  will  stick 
to  the  paper;  if  the  cement  is  just  sufficient  to  fill  the  voids,  the 
stain  will  be  distinct  but  not  blotchy;  and  if  the  mixture  is  too  lean, 
there  will  be  almost  no  stain.  The  test  is  inexact,  since  the  result 
depends  not  only  upon  the  proportion  of  the  cement  present,  but 
also  upon  the  temperature  and  the  amount  of  the  pressure.  This 
so-called  test  is  scarcely  any  better  than  judging  by  the  general 
appearance  of  the  mixture.  The  men  employed  at  the  plant  soon 
learn  to  judge  quite  accurately  of  the  proportions  by  the  appear- 
ance of  the  material  in  the  mixer. 

629.  Laying  the  Wearing  Coat.  The  mixed  cement  and  sand 
is  brought  upon  the  street  in  wagons  or  carts,  at  a  temperature  of 
about  280°  F.  It  is  dumped  upon  the  binder  course  (§  600),  and 
evenly  spread  over  the  surface  with  shovels  and  rakes.  Precautions 
should  be  taken  that  no  leaves,  straw,  pieces  of  paper,  cigar  stumps, 
etc.,  be  mixed  with  the  paving  mixture.  Great  care  must  be  exer- 
cised to  secure  an  even  distribution  of  the  loose  material,  as  other- 
wise there  wiU  be  depressions  or  elevations  in  the  finished  surface. 
The  depth  of  the  mixture  is  regulated  by  chalk  lines  on  the  curb, 
by  the  length  of  the  teeth  of  the  rake,  and  sometimes  by  rods  sup- 
ported on  feet  of  a  length  sufficient  to  bring  the  top  of  the  rod  to  the 
level  of  the  uncompacted  asphalt  mixture.  The  thickness  after 
being  rolled  varies  from  \\  to  2\  inches,  and  is  usually  2  inches. 
The  compression  in  rolling  varies  with  the  richness  of  the  mixture, 
the  leaner  mixtures  compressing  most,  but  is  usually  from  three 
tenths  to  four  tenths. 

The  first  compression  is  given  by  hand  rollers  and  tamping  irons. 
Two  sizes  of  hand  rollers  are  in  use :  the  lighter  is  30  inches  in  diam- 
eter, has  a  24-inch  face,  weighs  1,000  pounds,  and  gives  a  pressure 
of  42  pounds  per  linear  inch  of  face;  the  heavier  is  28  inches  in 
diameter,  has  an  18-inch  face,  weighs  1,400  pounds,  and  gives  a 
pressure  of  77  pounds  per  linear  inch.     Fig.  115,  page  417,  shows 


ART.   2.] 


SHEET   ASPHALT    PAVEMENTS. 


417 


a  hand  roller  with  a  fire  pot  inside  for  heating  it.     Tamping  irons 
are  used  around  man-hole  covers,  near  the  curb,  etc.,  where  the 


Fig.  115.— Hand  Asphalt-roller  with  Fire  Pot. 

roller  can  not  be  conveniently  used.     Fig.  116  shows  two  forms 
of  asphalt  tampers.      The  larger  has  a  face  about  8  inches  in 


Fig.  116.— Tampers  for  Asphalt  Pavements. 

diameter  and  weighs  about  30  pounds;  and  the  smaller  has  a  face 
about  2£"  X  5J",  and  weighs  about  18  pounds.     The  former  is  Used 


418  ASPHALT   PAVEMENTS.  [CHAP.   XIII. 

for  general  work;  and  the  latter  next  to  curbs,  street-car  rails,  etc. 
The  tamping  irons  are  heated  in  a  fire  in  an  iron  basket  which  is 
moved  from  place  to  place  on  wheels.  The  original  method  of  com- 
pression was  first  to  run  a  hand  roller  (whose  surface  was  prevented 
from  taking  up  any  of  the  sticky  mixture  by  being  oiled  with  kero- 
sene) rapidly  over  the  surface,  four  men  being  employed  for  this 
work.  This  method  is  still  employed  to  a  certain  extent,  but  it  has 
been  improved  upon  and  superseded  in  part  by  a  form  of  roller 
which  is  attached  to  the  front  of  the  steam  roller,  and  which  is 
heated  by  steam.  It  is  guided  by  a  parallel  motion  from  the  steer- 
ing gear  of  the  steam  roller  and  does  away  with  the  necessity  of  any 
one's  walking  on  the  newly  laid  surface. 

After  the  first  compression  with  hand  rollers  and  tampers,  men 
with  hot  tamping  and  smoothing  irons,  Fig.  116  and  117,  proceed 


Fig.  117.— Asphalt  Smoothing  Irons. 

to  finish  the  gutters,  joints,  and  all  angles  and  edges  which  can  not 
be  reached  with  the  heavier  rollers.  The  gutters  are  tested  with 
straight  edges  to  detect  depressions,  and  any  inequalities  on  the 
surface  are  removed.  The  use  of  hot  smoothing  irons  and  hot 
rollers  should  be  discouraged,  since  it  is  impossible  always  to  have 
them  of  such  a  temperature  as  not  to  injure  the  pavement,  and 
since,  if  the  mixture  is  delivered  at  the  proper  temperature,  and 
the  raking  and  spreading  is  done  expeditiously,  they  are  unneces- 
sary. Experience  shows  that  the  surface  of  pavements  upon  which 
hot  smoothing  irons  were  used  scales  and  flakes  off,  while  the  sur- 
face of  pavements  laid  without  such  hot  tools  does  not  chip  and 
scale  off. 

The  first  compression  having  been  given,  some  natural  hydraulic 
cement  or  any  impalpable  mineral  matter  is  dusted  over  the  surface 


ART.   2.]  SHEET   ASPHALT    PAVEMEXTS.  419 

to  give  it  a  more  pleasing  color  and  to  prevent  adhesion  of  the  roller; 
and  then  the  surface  is  next  rolled  with  a  steam  roller  of  the  asphalt 
pattern  (Fig.  65,  page  225).  In  the  most  approved  method  the 
pavement  is  first  rolled  with  a  roller  weighing  about  5  or  6  tons,  and 
next  with  a  roller  weighing  10  or  12  tons.  Often  only  the  light 
roller  is  used.  If  the  street  is  wide  enough,  the  pavement  should  be 
rolled  transversely  as  well  as  longitudinally ;  and  if  this  is  not  pos- 
sible, the  roller  should  run  as  obliquely  as  possible,  so  that  any  little 
inequality  which  might  be  caused  by  the  roller's  moving  lengthwise 
may  be  taken  out  by  the  cross  action.  The  rolling  should  be  kept 
up  until  the  roller  leaves  no  mark,  a  result  which  usually  requires 
at  least  5  hours  for  each  one  thousand  square  yards  of  surface. 

The  rolling  should  closely  follow  the  spreading  of  the  material, 
so  that  it  shall  not  have  time  to  cool  before  the  final  compression  is 
obtained.  The  state  of  the  weather  also  is  an  element  to  be  con- 
sidered; for  if  a  strong  wind  be  blowing,  the  material,  spread  overNa 
broad  surface  only  2  or  3  inches  thick,  will  cool  much  more  rapidly 
than  on  a  calm  day  when  the  temperature  is  considerably  lower. 

When  the  rolling  is  completed,  the  pavement  may  be  thrown 
open.  Traffic,  if  not  of  too  heavy  vehicles,  is  an  advantage  to  a 
newly  laid  asphalt  pavement,  since  the  pressure  of  the  wheels  aids  in 
consolidating  the  wearing  coat  and  in  closing  the  surface,  a  result 
which  helps  to  retain  the  volatile  oils  and  prevents  the  entrance  of 
water.  Asphalt  pavements  in  unfrequented  streets  do  not  wear  so 
well  as  under  a  moderately  heavy  traffic. 

630.  The  top  of  the  binding  course  should  be  perfectly  dry  when 
the  wearing  coat  is  laid,  to  prevent  its  being  separated  from  the 
course  below  by  the  formation  of  steam.  Asphalt  should  not  be 
laid  in  cold  weather,  since  the  paving  mixture  ma}^  become  chilled 
between  the  mixing  plant  and  the  street,  and  particularly  when  it 
comes  in  contact  with  the  cold  foundation. 

The  chief  points  requiring  skill  in  the  working  of  the  asphalt  sur- 
face are :  (1)  in  avoiding  inequalities  of  the  surface,  especially  depres- 
sions which  prevent  the  rapid  removal  of  storm  water;  (2)  in  secur- 
ing a  very  thorough  consolidation  of  the  gutters,  which  otherwise  rot 
rapidly;  and  (3)  in  thorough  rolling.  The  asphalt  mixture  can  not 
be  fully  compacted  by  simple  pressure,  but  requires  the  kneading 
fiction  of  repeated  passages  of  the  roller.     The  lubricating  quality 


420  ASPHALT    PAVEMENTS.  [CHAP.   XIII. 

of  the  warm  asphalt  aids  in  this  action,  so  that  under  the  roller  the 
grains  of  sand  are  wedged  together  and  the  finer  particles  worked 
into  the  voids,  until  the  mass  becomes  more  dense  than  dry  sand 
alone  could  be  made.  This  is  proved  by  the  fact  that  if  all  the 
bitumen  be  extracted  from  a  fragment  of  pavement  of  known  vol- 
ume, it  is  found  to  be  quite  impossible  to  reduce  the  dry  sand  ob- 
tained to  as  small  a  volume  as  it  occupied  in  the  pavement. 

On  streets  with  flat  grades  the  gutters  do  not  drain  well ;  and  as 
moisture  is  likely  to  injure  asphalt,  the  gutter  is  painted  with  a  coat 
of  hot  asphalt  or  is  laid  with  hydraulic  cement  concrete,  stone,  or 
brick.  If  the  gutter  is  fairly  well  drained,  and  the  asphalt  is  thor- 
oughly compacted,  the  first  method  will  give  reasonably  good  re- 
sults. The  gutter  may  be  painted  with  a  swab  or  a  broom;  but  the 
work  is  most  easily  done  with  a  gutter  painter,  which  consists  of  a 
cast-iron  box  about  14  inches  square  having  a  slot  in  the  bottom, 
carried  by  a  rigid  handle  on  each  side. 

To  protect  the  asphalt  along  street-car  tracks  and  sidewalk 
crossing-stones,  where  there  are  vibrations  and  pounding  of  the 
wheels  of  vehicles,  it  is  customary  to  lay  a  line  of  granite  blocks  or 
vitrified  blocks — usually  headers  and  stretchers  alternately.  The 
toothing  of  the  bricks  or  the  stone  blocks  into  the  asphalt' adjacent 
to  car  tracks,  gutters,  etc.,  is  to  do  away  with  the  continuous  joint 
and  thus  to  prevent  wheels  from  wearing  a  rut ;  but  there  is  so  much 
difficulty  in  sufficiently  compacting  the  asphalt  between  the  pro- 
jecting blocks,  that  the  toothing  is  of  doubtful  value.  After  sev- 
eral years'  trial  it  has  been  abandoned  in  Washington,  D.  C. 

631.  Causes  of  Failures  of  Asphalt  Pavements.  Asphalt 
pavements  have  frequently  failed ;  but  when  it  is  remembered  that 
the  industry  is  new  and  has  been  rapidly  developed,  and  that  there 
was  no  precedent,  and  that  therefore  the  proportions  and  the 
methods  of  mixing  and  laying  had  to  be  determined  by  actual  expe- 
rience, it  is  not  astonishing  that  some  pavements  should  fail.  But  the 
permissible  variation  in  the  various  ingredients  and  in  the  different 
details  of  the  work  is  so  small,  that  if  good  results  are  expected,  the 
utmost  care  must  always  be  exercised.  Asphalt  pavements  have 
some  advantages  not  possessed  by  any  other  forms  of  pavement, 
and  will  doubtless  always  be  laid  to  a  considerable  extent.  There- 
fore the  engineer  who  is  responsible  for  such  work  should  be  welL 


ART.   2.]  SHEET    ASPHALT    PAVEMENTS.  431 

informed  as  to  the  various  steps  in  the  construction  of  this  class  of 
pavements. 

Unfortunately  the  custom  has  been  to  contract  with  asphalt 
paving  companies  to  lay  asphalt  pavements  and  to  guarantee  them 
for  a  term  of  years,  and  consequently  the  municipalities  have  as  a 
rule  made  no  analysis  of  either  the  asphalt  or  the  flux  used,  and 
have  not  examined  the  sand  or  limestone  dust  nor  paid  any  atten- 
tion to  the  methods  employed  in  mixing  and  laying  the  materials. 
The  result  is  that  there  are  no  public  records  showing  the  history  of 
the  pavement,  and  therefore  it  is  often  impossible  to  determine  the 
cause  of  either  failure  or  success.  City  officials  should  carefully 
analyze  the  ingredients  and  examine  the  method  of  mixing  and  lay- 
ing the  materials,  not  only  to  secure  the  best  possible  pavement, 
but  also  to  obtain  data  to  serve  as  a  guide  for  similar  work  in  the 
future.  Owing  to  differences  in  materials,  climate,  and  traffic,  a 
considerable  part  of  such  data  must  be  obtained  for  each  particular 
city. 

On  account  of  the  lack  of  such  data,  it  is  often  impossible  to 
determine  certainly  the  cause  of  the  failure  in  any  particular  case. 
The  following  are  some  of  the  principal  causes  of  the  failure  of 
asphalt  pavements: 

632.  Unsuitable  Material.  The  service  demanded  of  a  pave- 
ment is  quite  severe,  and  to  attain  a  reasonable  success  each  of  the 
three  components — the  asphalt,  the  flux,  and  the  sand — must  be 
carefully  selected. 

633.  Asphalt.  The  asphalt  may  have  been  so  changed  by  nat- 
ural causes  as  to  possess  little  or  no  cementing  power  (see  §  649); 
or  it  may  have  contained  a  soluble  salt  which  was  subsequently 
dissolved  by  rain  water,  thus  leaving  the  pavement  porous  and 
subjecting  it  to  the  disintegrating  effect  of  the  acids  and  oxygen  in 
the  rain  water  as  well  as  to  the  effect  of  the  freezing  of  the  water  in 
the  pores  of  the  pavement. 

If  the  asphalt  is  deficient  in  cementing  power  or  is  unduly  dis- 
integrated by  the  action  of  acfds,  oxygen,  etc.,  this  fact  will  gener- 
ally first  be  indicated  by  a  premature  tendency  of  the  pavement  to 
crack,  particularly  during  cold  weather  (see  §  654). 

634.  Flux.  The  fluxing  -agent  may  not  have  been  a  solvent  of 
both  of  the  constituent  parts  of  the  bitumen  of  the  asphalt,  and  may 


422  ASPHALT  PAVEMENTS.  [CHAP.  XIII. 

have  formed  a  mechanical  mixture  instead  of  a  chemical  union  (see 
§  604).  Or  the  flux  may  have  contained  volatile  oils  which  finally 
evaporated  from  the  pavement  and  left  it  porous  and  devoid  of 
cementing  power  (see  §  604).  The  use  of  an  improper  fluxing  agent 
will  produce  much  the  same  effect  as  an  asphalt  deficient  in  binding 
power  (§  586). 

635.  Sand.  The  sand  may  have  been  too  coarse,  or  too  fine,  or 
have  contained  too  much  clay  or  vegetable  matter  (see  §  621-24). 
If  the  sand  is  too  coarse,  or  is  dirty,  the  pavement  will  have  a  ten- 
dency to  crack.  If  the  sand  is  too  fine,  or  is  deficient  in  sharpness, 
the  pavement  will  have  a  tendency  to  roll  or  push  out  of  place — 
particularly  under  a  heavy  traffic, — and  the  surface  may  be  marked 
by  the  traffic  in  hot  weather. 

636.  Free  Oil  in  Binder.  The  binder  may  contain  an  oil  which 
will  subsequently  be  absorbed  by  the  wearing  coat  and  cause  the 
asphalt  to  disintegrate.  This  is  more  likely  to  occur  with  a  coal-tar 
than  with  an  asphalt  binder.  Pavements  affected  this  way  give 
signs  of  disintegration  by  a  slight  depression  over  the  affected  spot, 
and  in  time  numbers  of  small  cracks  appear,  running  parallel  with 
the  street,  which  gradually  increase  in  prominence,  accompanied 
with  transverse  cracks,  until  the  pavement  has  the  appearance  of 
alligator  skin. 

637.  Improper  Manipulation.  Even  though  the  materials  may 
be  the  best,  there  is  an  abundant  opportunity  for  failure  through 
improper  manipulation  in  heating  and  mixing  the  materials. 

638.  Too  High  Heat.  The  asphalt  may  have  been  damaged  by 
overheating  or  "burning."  The  burning  of  the  asphalt  causes  the 
pavement  to  disintegrate  on  the  surface  in  spots  during  cold  weather, 
and  may  be  revealed  by  a  brittleness  and  a  tendency  to  crack  while 
being  rolled.  Excessive  heat  converts  the  petroline,  or  cementi- 
tious  constituent  of  asphalt,  into  asphaltine  which  is  devoid  of 
cementing  properties,  and  by  so  much  reduces  the  cementing 
quality — the  vital  element — of  the  asphalt.  This  overheating  may 
take  place  during  the  refining  (see*§  590),  or  during  the  flu/dng 
(see  §  609),  or  in  mixing  the  asphaltic  cement  and  the  sand  (see 
§  627). 

•  In  practice  there  is  much  carelessness  in  melting  the  asphalt. 
Not  infrequently  the  kettle  is  mounted  within  brick  walls  directly 


ART.   2.]  SHEET   ASPHALT   PAVEMENTS.  423 

over  a  fire  which  comes  in  contact  with  only  a  comparatively  small 
part  of  the  heating  surface,  in  which  case  it  is  highly  improbable  that 
the  firing  will  be  done  so  evenly  and  slowly  as  not  to  burn  at  least 
part  of  the  material.  The  fire  should  not  be  allowed  to  come  in 
direct  contact  with  the  melting  kettle  or  tank,  thereby  guaranteeing 
that  no  portion  of  the  asphalt  can  be  burned.  When  the  asphalt  has 
been  badly  burned,  it  will  be  revealed  by  a  brittleness  during  roll- 
ing; but  there  is  no  way  of  determining  a  lesser  degree  of  burning 
although  it  still  may  be  sufficient  to  cause  a  serious  defect  which 
will  finally  develop  into  cracks  and  rotten  spots.  Therefore  the 
inspector  should  insist  upon  a  method  of  melting  that  will  insure  an 
unburned  product.  It  is  sometimes  specified  that  the  asphalt  shall 
be  heated  by  steam. 

The  overheating  of  the  asphalt  may  be  produced  also  by  over- 
heating the  sand  (see  §  627).  Every  precaution  should  be  used  to 
have  each  batch  of  sand  heated  uniformly  throughout,  and  its  tem- 
perature should  be  taken  before  mixing  it  with  the  asphalt.  As  a 
further  check,  the  temperature  of  each  load  of  paving  compound 
sent  to  the  street  should  be  taken  and  recorded  at  the  mixing 
plant. 

639.  Improper  Consistency.  The  paving  cement  may  have  been 
mixed  too  hard  or  too  soft  (see  §  613).  If  the  cement  is  too  hard, 
the  pavement  will  have  a  tendency  to  crack  during  cold  weather; 
and  if  it  is  too  soft,  it  will  push  out  of  place  and  form  rolls  or  waves 
under  the  traffic. 

640.  Insufficient  Bitumen.  The  wearing  coat  may  not  have 
contained  sufficient  cementing  material.  It  should  contain  at  least 
9  per  cent  of  bitumen  soluble  in  carbon  bisulphide  (see  §  611). 
Within  the  limits  imposed  by  the  proper  softness  and  hardness  of  the 
pavement,  the  greater  the  per  cent  of  asphalt  the  greater  the  life  of 
the  pavement;  and  consequently  contractors  in  laying  a  pavement 
under  a  long-time  guarantee  use  the  maximum  amount  of  asphaltic 
cement,  but  when  the  maintenance  period  is  short  they  generally  use 
the  minimum.  Owing  to  improper  manipulation  the  amount  of 
bitumen  is  likely  to  be  too  small,  since  in  fluxing  the  tendency  is 
for  the  bitumen  to  rise  and  the  mineral  impurities  to  settle;  and 
consequently  if  the  tank  is  worked  too  low,  there  is  a  likelihood  that 
the  last  material  taken  from  the  tank  will  contain  too  small  a  oro- 


424  ASPHALT   PAVEMENTS.  |_CHAP.   XIII. 

portion  of  bitumen  and  too  large  a  proportion  of  sediment.  In- 
sufficient bitumen  has  substantially  the  same  effect  upon  the  pave- 
ment as  improper  asphalt. 

641.  Inadequate  Mixing.  The  ingredients  of  the  wearing  coat 
may  not  have  been  sufficiently  mixed.  It  is  important  that  each 
grain  of  sand  shall  be  entirely  surrounded  by  the  cementing  mate- 
rial, so  that  no  two  pieces  shall  come  into  actual  contact.  If  the 
mixing  is  not  well  done,  the  pavement  will  disintegrate  in  spots. 

642.  Rich  Binder.  If  an  excess  of  asphalt  or  coal  tar  is  used  in  the 
binder  course,  it  is  likely  to  work  to  the  surface  of  that  course  and 
then  being  absorbed  by  the  wearing  coat  cause  it  to  disintegrate. 
This  cause  of  failure  manifests  itself  by  irregular  blotches  on  the 
surface  of  the  pavement. 

643.  Cement  Chilled.  The  mixture  for  the  wearing  coat  may 
become  chilled  while  being  transported  from  the  mixing  plant  to  the 
street.  To  prevent  this  possibility,  the  temperature  of  each  load 
should  be  taken  just  before  it  is  laid.  The  material  may  also  be- 
come chilled  by  a  delay  in  tamping  and  rolling,  or  by  attempting  to 
work  during  too  cold  weather  or  during  the  prevalence  of  a  high 
wind.  A  batch  of  chilled  mixture  will  cause  a  weak  spot  in  the 
pavement. 

644.  Separation  of  Cement  and  Sand.  If  the  distance  from  the 
plant  to  the  street  is  long  or  there  is  unusual  delay,  some  of  the 
asphaltic  cement  may  work  down  to  the  bottom  of  the  load,  and 
when  the  material  is  dumped  there  will  be  both  rich  and  lean  spots 
— both  of  which  are  equally  objectionable.  The  rich  spots  will 
have  a  tendency  to  roll  or  crowd  toward  the  gutter;  and  the  lean 
spots  will  have  a  tendency  to  disintegrate  under  traffic. 

645.  Damp  or  Dirty  Foundation.  The  wearing  coat  may  have 
been  laid  on  a  dirty  or  damp  foundation,  and  therefore  have  been 
prevented  from  uniting  firmly  with  the  foundation  (see  §  598). 
This  condition  will  be  revealed  by  a  tendency  of  the  pavement  to 
roll  or  push  out  of  place  while  sound  and  firm  on  the  surface. 

646.  Inadequate  Compression.  The  wearing  coat  may  not  have 
received  sufficient  compression.  The  surface  must  be  thoroughly 
compacted — particularly  in  the  gutters — to  keep  out  rain  water 
and  the  acids  and  oxygen  dissolved  in  it.  The  effect  of  oxidation 
is  gradually  to  convert  the  petroline  into  asphaltine,  and  to  leave 


ART.  2.]  SHEET   ASPHALT   PAVEMENTS.  425 

the  bitumen  of  the  flux  as  the  only  binding  constituent  of  the  mix- 
ture; and  therefore  the  pavement  will  have  a  general  tendency  tt 
crack  and  disintegrate. 

647.  Natural  Causes.  All  materials  in  nature  are  undergoing 
changes  due  to  the  action  of  the  elements,  and  asphalt  pavements 
are  no  exception.  The  following  are  some  of  the  principal  causes 
leading  to  the  gradual  deterioration  of  such  pavements. 

648.  Ordinary  Wear.  The  pavement  may  decrease  in  thickness 
due  to  loss  of  material  by  the  abrasion  of  hoofs  and  wheels;  but 
since  the  surface  is  smooth  and  somewhat  elastic  the  loss  by  wear 
is  almost  imperceptible.  In  some  cases  the  pavement  decreases  in 
thickness  with  use,  but  the  decrease  is  due  to  consolidation  rather 
than  to  loss  of  material. 

649.  Natural  Decay.  All  asphalts  gradually  lose  their  cement- 
ing power  with  age  by  volatilization,  evaporation,  and  oxidation. 
The  pavement  is  peculiarly  exposed  to  the  action  of  the  sun's  heat, 
and  to  the  combined  action  of  rain  water,  acids,  oxygen,  and  frost. 
The  greater  the  cementing  power  of  the  asphalt  originally  and  the 
softer  the  cement,  the  longer  the  pavement  will  resist  the  influence 
of  volatilization  and  evaporation;  and  the  more  nearly  the  voids  of 
the  sand  are  filled  with  cement  and  the  more  firmly  the  pavement 
is  consolidated,  the  longer  it  will  resist  the  action  of  water,  acids, 
oxygen,  and  frost.  The  general  decay  of  the  asphalt  will  be  indi- 
cated by  a  tendency  of  cracks  to  form  during  cold  weather  (see 
§  654),  particularly  during  a  sudden  and  extreme  drop  in  the  tem- 
perature. 

650.  Weak  Foundation.  A  weak  or  improperly  prepared  founda- 
tion by  unequal  settlement  or  settlement  in  spots  will  cause  cracks 
and  depressions  in  the  surface  which  under  traffic  will  speedily  en- 
large and  cause  the  pavement  soon  to  break  up. 

651.  Porous  Foundation.  A  porous  foundation  permits  the 
ground  water  to  rise,  by  capillary  action  and  possibly  also  by  hydro- 
static pressure,  to  the  underside  of  the  wearing  coat,  where  by 
freezing  it  may  break  the  bond  between  the  top  layer  and  the  base, 
and  thus  permit  the  wearing  coat  to  be  pushed  out  of  place  and 
broken.  This  effect  has  been  known  to  occur  with  a  concrete 
foundation;  but  it  is  not  likely  to  occur  with  good  concrete.  If 
a  section  of  pavement  disintegrating  from  this  cause  be  examined, 


426  ASPHALT  PAVEMENTS.  [CHAP.  XLH. 

there  will  be  found  a  layer  of  perfectly  sound  and  good  material  at 
the  surface,  while  the  lower  side  of  the  wearing  coat  will  show  evi- 
dence of  being  disintegrated  by  water — that  is,  the  sand  will  appear 
clean  and  white  in  spots  as  though  there  had  been  an  insufficiency 
of  asphalt  cement  to  cover  it.  The  concrete  base  under  the  affected 
spot  will  generally  be  found  to  be  damp  or  even  wet.  The  recur- 
rence of  this  defect  may  be  prevented  by  underdraining  the  soil. 

652.  Leaky  Joints,  Lack  of  a  water-tight  joint  between  the 
asphalt  surface  and  the  curb,  the  gutter,  manhole  covers,  crossings, 
street-car  rails,  etc.,  may  permit  the  water  to  enter  the  lower  and 
less  compact  part  of  the  wearing  coat,  where  by  its  solvent  action 
and  also  by  freezing  it  may  do  material  damage.  It  is  nearly  im- 
possible to  keep  these  joints  tight,  particularly  adjacent  to  the 
street-car  rails.  The  damage  often  extends  a  considerable  distance 
from  the  place  where  the  water  enters. 

The  disintegrating  effect  of  water  depends  chiefly,  if  not  wholly, 
upon  the  contained  oxygen,  and  the  effect  upon  different  asphalts 
varies  with  the  proportion  of  soluble  salts  present.  Apparently 
Trinidad  asphalt  is  acted  upon  to  a  greater  extent  by  water  than 
any  other  asphalt ;  *  but  it  is  claimed  f  that  this  deterioration  can 
be  greatly  reduced  by  removing  the  soluble  salts  in  the  refining 
process,  at  a  comparatively  small  expense.  For  the  results  of  ex- 
periments showing  a  great  variation  in  the  effect  of  water  and  of 
frost  upon  different  asphalt  pavements,  see  Engineering  News, 
Vol.  44,  p.  113-15.  In  these  experiments,  two  samples  of  asphalt 
blocks  lost  considerably  less  than  any  one  of  the  seven  samples  of 
sheet  asphalt. 

653.  Illuminating  Gas.  Ordinary  illuminating  gas,  escaping 
from  leaky  pipes  under  the  pavement,  is  absorbed  by  the  pavement, 
and  causes  the  disintegration  of  the  asphalt  4  It  has  been  deter- 
mined   experimentally  that  "one  volume  of  asphalt  cement  will 

*  The  Action  of  Water  on  Asphalt,  by  George  C.  Whipple  and  Daniel  D.  Jackson. 
A  paper  read  before  the  Brooklyn  (N.  Y.)  Engineers'  Club,  March  8,  1900 ;  and  pub- 
lished in  Engineering  News,  Vol.  43,  p.  187-88. 

f  A.  W.  Dow,  Inspector  of  Asphalts,  Annual  Report  of  Operations  of  Engineer- 
ing Departemnt  of  the  District  of  Columbia,  1901,  p.  156. 

%  For  the  results  of  a  very  careful  investigation  of  this  subject,  see  a  report  by 
A.  W.  Dow,  in  Annual  Report  of  the  Operations  of  the  Engineering  Department 
of  the  District  of  Columbia  for  the  year  ending  June  30,  1899,  p.  111-112. 


ART.  2.  J  SHEET   ASPHALT   PAVEMENTS.  42? 

absorb  forty-five  volumes  of  illuminating  gas  in  something  over  a 
month;  and  it  has  been  demonstrated  practically  that  pavements 
do  actually  absorb  illuminating  gas  from  leaky  mains,  in  one  in- 
stance 1;000  c.c.  of  pavement  giving  off  500  c.c.  of  gas  which  it  had 
absorbed.  It  has  been  shown  that  asphalt  is  much  softened  by 
absorbing  gas,  the  ordinary  asphalt  becoming  as  soft  as  maltha  after 
being  in  an  atmosphere  of  illuminating  gas  for  several  months. 
There  is  but  one  way  to  stop  the  disintegration  of  a  pavement  from 
this  cause,  and  that  is  to  stop  the  leak  of  gas. ' '  * 

Pavements  affected  by  illuminating  gas  first  give  signs  of  their 
disintegration  by  a  slight  depression  over  the  affected  spots,  later 
fine  cracks  appear  parallel  to  the  line  of  the  street,  and  finally  the 
surface  coat  begins  to  crowd. 

654.  Cracks.  Long  irregular  cracks  in  the  wearing  surface 
frequently  occur  during  cold  weather.  They  usually  start  at  the 
gutter  or  man-hole  frame,  and  gradually  extend  across  the  street. 
They  are  often  found  at  the  joint  between  an  old  and  a  new  pave- 
ment or  at  the  joint  made  between  one  day's  work  and  another. 
These  cracks  are  due  to  the  contraction  of  the  wearing  surface,  and 
should  not  be  confounded  with  cracks  due  to  the  failure  of  the 
foundation  (§  650).  Usually  these  cracks  do  not  occur  until  the 
pavement  is  two  or  three  years  old ;  at  least  they  are  most  likely  to 
occur  in  an  old  pavement — one  in  which  the  asphalt  has  lost  part  of 
its  cementing  power  by  age.  These  cracks  appear  sooner  and  in- 
crease more  rapidly  on  a  street  having  only  a  light  traffic.  When 
the  pavement  is  subjected  to  a  continuous  traffic,  the  asphalt  sur- 
face, which  is  more  or  less  plastic  at  all  temperatures,  is  kept  from 
cracking  by  the  constant  kneading  action  of  the  traffic.  Again, 
when  an  asphalt  surface  has  but  little  or  no  traffic,  it  becomes  more 
porous  owing  to  expansion  and  contraction  from  heat  and  cold 
without  the  compression  due  to  traffic,  and  as  a  consequence  is 
materially  weakened.  If  cracks  occur  on  a  street  having  a  fair 
amount  of  traffic,  it  is  evident  that  the  paving  mixture  used  is  at 
fault;  either  there  was  not  enough  bitumen  or  the  asphalt  cement 
was  too  hard. 


*A.  W.  Dow,  in  Annual  Report  of  the  Operations  of  the  Engineering  Department 
of  the  District  of  Columbia,  1899,  p.  112. 


428  ASPHALT    PAVEMENTS.  [CHAP.  XIII. 

Some  engineers  leave  expansion  joints,  i.  e.,  cut  the  wearing 
coat  through,  "at  intervals  to  prevent  these  irregular  contraction 
cracks.  Such  a  procedure  is  of  doubtful  propriety,  since  the  pave- 
ment if  properly  constructed  will  not  crack  in  several  years  under 
the  most  adverse  conditions,  and  then  only  at  long  intervals  and 
generally  at  some  old  joint;  and  if  the  pavement  is  improperly 
made,  the  expansion  joint  will  have  only  a  slight  tendency  to  pre- 
vent these  irregular  cracks.  The  principle  of  the  expansion  joint  is 
not  applicable  to  materials  with  no  structural  strength,  like  asphalt 
mixtures.  These  joints  are  not  only  useless,  but  really  detrimental 
to  a  pavement;  they  are  only  another  form  of  the  defect  they  are 
intended  to  remedy,  for  they  are  crevices  which  retain  mud  and 
water  which  tend  to  rot  the  asphalt,  and  the  edges  of  the  joints  are 
easily  broken  down  by  traffic  which  also  widens  the  crack. 

It  is  particularly  unfortunate  that  an  asphalt  pavement  is  likely 
to  crack,  since  not  only  do  the  edges  of  the  cracks  disintegrate,  but 
the  cracks  permit  water  to  reach  the  interior  of  the  pavement 
where  it  has  a  deteriorating  effect. 

655.  Shifting  under  Traffic.  The  surface  coat  sometimes  flows 
under  traffic,  i.  e.,  pushes  lengthwise  of  the  street  into  waves  or 
crowds  toward  the  gutter.  This  defect  occurs  in  pavements  having 
too  soft  a  wearing  surface,  or  where  there  is  a  defective  bond  either 
between  the  base  and  the  binder,  or  between  the  binder  and  the 
wearing  surface.  This  is  a  defect  that  is  impossible  to  guard  against 
entirely  on  a  street  having  very  heavy  traffic,  and  especially  where 
the  traffic  is  confined  to  a  narrow  section  of  the  street ;  but  this  de- 
fect is  inexcusable  on  streets  having  only  moderately  heavy  traffic. 
This  flowing  is  commonly  caused  by  the  surface  of  the  hydraulic 
concrete  base  under  the  pavement  being  too  smooth,  which  is  the 
case  where  gravel  concrete  is  used  or  where  a  stone-and-gravel  con- 
crete is  so  rich  that  its  surface  is  covered  with  mortar  that  was 
brought  to  the  top  by  ramming.  Unless  the  binder  and  the  surface 
mixtures  are  made  very  hard,  a  condition  which  makes  the  pave- 
ment likely  to  crack,  the  wearing  coat  will  slide  on  such  a  base  if 
there  is  much  traffic.  Pavements  often  roll  from  a  defect  in  the 
binder — either  because  it  was  too  rich  in  asphaltic  cement,  or  be- 
cause it  was  dirty  when  the  wearing  surface  was  laid. 

656.  Damage  by  Bonfires.     Another  cause  of  damage  to  asphalt 


ART.   2.]  SHEET    ASPHALT    PAVEMENTS.  429 

pavements  is  the  building  of  fires  upon  them.  Of  course  this  ought 
never  to  occur,  but  even  in  the  best  regulated  municipalities  it  does 
happen. 

657.  METHOD  OF  REPAIRING.  The  repairs  necessitated  in 
the  maintenance  of  an  asphalt  pavement  may  be  classified  as 
follows:  (1)  those  due  to  a  settlement  of  the  subgrade;  (2)  those 
due  to  a  disintegration  of  the  pavement  in  spots;  (3)  those  due  to 
the  formation  of  waves ;  (4)  those  due  to  the  formation  of  cracks ; 
(5)  the  painting  of  the  gutter;  and  (6)  the  remedying  of  defects 
next  to  the  street-car  rails,  crossing  stones,  man-hole  covers,  etc. 

658.  Settlement  of  Subgrade.  It  is  generally  conceded  that 
the  majority  of  repairs  are  necessitated  by  the 'settlement  of  the 
foundation  over  trenches.  To  repair  these  defects,  it  is  neces- 
sary to  remove  the  wearing  coat,  the  binder,  and  the  foundation, 
and  then,  after  having  consolidated  the  material  in  the  trench  (see 
§  450),  to  relay  the  pavement  much  as  in  the  original  construction. 
The  edges  of  the  binder  course  and  also  of  the  wearing  coat  should 
be  thoroughly  covered  with  a  thin  coat  of  asphaltic  cement  to 
secure  a  perfect  union  of  the  old  and  the  new  material.  The  stone 
in  the  old  concrete  should  not  be  used  again,  since  the  mortar 
makes  a  surplus  of  fine  material  and  would  prevent  a  firm  adhesion 
of  the  new  cement  to  the  stone.  Both  the  binder  course  and  the 
wearing  coat  should  be  thoroughly  tamped  or  rolled.  Owing  to 
the  difficulty  of  fully  consolidating  the  patch,  it  is  left  a  trifle  high 
to  prevent  a  possible  depression. 

659.  Disintegration  in  Spots.  If  the  wearing  coat  disintegrates 
in  spots,  or  forms  "  macaroons,"  from  any  of  the  causes  described  in 
§  631-53,  the  affected  part  must  generally  be  cut  out,  since  it  is 
usually  affected  to  its  full  depth.  If  the  binder  course  is  the  cause 
of  the  deterioration  (see  §  642),  it  also  must  be  cut  out.  The  new 
material  is  to  be  laid  as  described  in  the  preceding  paragraph.  If 
the  disintegration  does  not  extend  to  the  full  depth  of  the  wearing 
coat,  the  repair  may  be  made  by  "  skimming,"  as  described  in  the 
succeeding  paragraph. 

660.  Formation  of  Waves.  If  the  wearing  coat  has  shifted  under 
the  traffic  so  as  to  form  waves,  i.  e.,  until  it  is  thicker  in  some  parts 
than  others,  or  if  the  wearing  coat  has  crowded  towards  the  gutter,  it 
may  be  necessary  to  melt  off  a  portion  of  the  high  part,  and  also  to 


430 


ASPHALT    PAVEMENTS. 


[CHAP.   XIII. 


re-surface  the  thin  part.  This  is  called  skimming.  The  asphalt 
is  melted  off  either  with  an  open  grate  on  low  wheels  in  which 
coke  is  burned;  or  with  a  special  heater  having  a  tank  for  gaso- 
lene; a  hood  over  the  burner,  and  an  asbestos  mat  to  protect 
the   adjacent  pavement.     Fig.  118   shows    the   form   of  surface 


Fig.  118.— Surface  Heater  for  Repairing  Asphalt  Pavements. 


heater  in  common  use.  The  surface  is  heated  until  the  affected 
portion  can  be  raked  off;  and  then  new  material  is  added  to  bring 
the  pavement  to  its  proper  thickness.  There  is  considerable  differ- 
ence of  opinion  as  to  the  possibility  of  doing  good  work  by  this 
method. 

661.  Cracks.  When  cracks  have  formed  in  the  wearing  coat, 
all  the  loose  material  is  cut  off,  the  crack  is  cleaned  out,  and  hot 
asphaltic  cement  is  poured  in. 

662.  Painting  Gutters.  Owing  to  the  disintegrating  effect  of 
water,  asphalt  gutters  usually  require  comparatively  frequent  re- 
pairs either  by  painting  (§  630)  with  asphalt  rich  in  bitumen,  or  by 
skimming  (§  660),  or  by  removing  the  wearing  coat  and  re-laying 
it,  using  an  asphalt  richer  in  bitumen  than  that  in  the  remainder  of 
the  pavement. 

663.  Recording  Repairs.  The  present  practice  is  to  make  the 
repairs  to  asphalt  pavements  by  contract  with  a  guarantee  of  the 
work  for  a  number  of  years;  and  therefore  it  is  important  that  a 
record  should  be  kept  of  the  area  and  location  of  the  several  patches 


ART.   2.]  SHEET   ASPHALT   PAVEMENTS.  431 

and  also  of  the  date  when  each  was  made.  This  is  done  by  dividing 
the  pavement  into  imaginary  squares,  of  say,  10  feet  on  a  side ;  and 
then  when  a  patch  is  to  be  made,  one  or  more  of  these  squares  should 
be  located  by  chalk  marks  on  the  pavement,  and  the  boundary 
of  the  patch  should  be  sketched  in  a  cross-ruled  note-book.  The 
records  of  the  individual  patches  are  afterwards  platted  upon  a 
single  sheet  to  see  that  a  subsequent  patch  does  not  overlap  one  for 
which  the  guarantee  has  not  expired. 

664.  Using  Old  Materials.  In  some  cities  it  is  customary  to 
permit  the  re-use  of  the  old  asphalt,  but  this  is  of  doubtful  wisdom, 
since  usually  the  repair  is  required  by  the  inferiority  of  the  old 
material,  and  since  it  is  likely  to  be  over-heated  in  being  removed. 
If  the  asphalt  is  not  damaged,  and  is  cut  out  with  an  ax,  it  may  be 
used  again,  provided  (1)  the  pieces  are  kept  clean,  (2)  it  is  re- 
heated slowly  and  carefully,  and  (3)  new  asphalt  is  added  to  flux 
the  old.  It  is  difficult  to  melt  old  material  without  burning  it.  and 
it  is  also  difficult  to  secure  a  uniform  mixture. 

665.  Specification  for  Repairs.  Asphalt  pavements  are  usually 
maintained  by  contract,  and  therefore  it  becomes  important  to  have 
some  standard,  particularly  at  the  end  of  the  contract  period,  by 
which  to  judge  of  the  liability  for  repairs.  The  following  specifica- 
tions have  been  recommended  for  this  purpose  by  a  committee  of 
the  American  Society  of  Municipal  Improvements.* 

"  Sec.  1.  The  pavement  shall  not  be  reduced  more  than  one  fourth  inch 
from  the  original  thickness  at  the  end  of  the  first  five  years,  or  more  than 
one  half  inch  from  the  original  thickness  at  the  end  of  the  first  ten  years. 
(This  requirement  shall  not  apply  to  pavements  constructed  of  rock  asphalt, 
as  this  material  does  not  receive  its  ultimate  compression  for  a  considerable 
period  after  being  laid.) 

"  Sec.  2.  Places  which  show  a  disintegration  of  the  material  shall  be 
removed  to  the  binder  or  concrete  foundation,  as  found  necessary,  and  be 
replaced  with  new  material  having  the  same  thickness  and  conforming  to 
the  adjacent  pavement. 

"  Sec.  3.  All  elevations  or  depressions  three  eighths  of  an  inch  or  more 
above  or  below  the  general  surface  of  the  street  shall  be  brought  to  the  same 
elevation  as  the  general  surface,  these  elevations  and  depressions  to  be  deter- 
mined by  measuring  from  a  straight  edge  four  feet  in  length,  placed  on  the 

*  Proc.  Fourth  Annual  Convention  (1897),  p.  142-43. 


432  ASPHALT    PAVEMENTS.  [CHAP.   XIII. 

surface  of  the  pavement  parallel  to  the  line  of  curbing.*  (In  making  such 
repairs  the  process  known  as  "skimming"  may  be  employed  ) 

"  Sec.  4.  Where  elevations  or  depressions  are  due  to  the  failure  of  the 
concrete  foundation  from  any  cause,  the  asphalt  and  concrete  shall  both  be 
removed  a  length  and  width  to  include  the  entire  defect.  If  the  failure  is 
due  to  buckling  of  the  concrete,  the  new  foundation  shall  consist  of  broken 
stone  thoroughly  compacted,  and  of  the  same  thickness  as  the  original  con- 
crete. In  all  other  cases  a  new  foundation  of  concrete  shall  be  placed  of 
the  same  thickness  as  the  original  construction.  Upon  the  foundation  shall 
be  placed  a  pavement  of  the  same  thickness  as  the  adjacent  surfaces. 

"  Sec.  5.  Cracks  which  show  any  indication  of  disintegration,  or  which 
are  three  eighths  of  an  inch  or  more  in  width,  shall  be  cut  out  to  the  binder 
or  concrete  foundation,  as  found  necessary,  a  length  and  width  sufficient  to 
include  the  entire  portion  affected ;  and  this  portion  shall  be  replaced  with 
new  material  of  the  same  quality  and  thickness  as  in  the  pavement  adjacent 
thereto. 

"  Sec.  6.  Should  it  be  found  necessary  to  replace  twenty-five  per  cent  or 
more  of  any  section  of  the  street  with  new  material,  the  entire  section  shall 
be  re-surfaced." 

666.  Cost  of  Sheet  Asphalt  Pavements.  Any  general 
statement  of  the  cost  of  any  engineering  construction  can  be  only 
approximately  true  in  in  any  particular  case,  owing  to  variations  in 
local  conditions,  the  prices  of  material  and  labor,  etc.;  and  any 
accurate  statement  concerning  the  cost  of  asphalt  pavements  is 
rendered  still  more  difficult  by  the  existence  of  artificial  conditions 
which  control  prices,  and  also  by  the  fact  that  the  public  has  little 
or  no  reliable  information  as  to  the  actual  cost  of  laying  asphalt 
pavements.  During  the  early  history  of  the  asphalt  paving  indus- 
try, a  single  company  imported  and  in  its  own  name  constructed 
nearly  all  the  asphalt  pavements  laid  in  this  country,  using  exclu- 
sively asphalt  from  the  island  of  Trinidad.  Later  this  company 
obtained  an  almost  complete  monopoly  of  this  asphalt.  It  is 
claimed,  apparently  wdth  justification,  that  this  company  then  or- 
ganized a  number  of  subsidiary  companies,  and  that  for  a  number 
of  years  thereafter  there  was  practically  no  competition  in  the 
asphalt  paving  business,  except  in  name.  Later  the  discovery 
of  other  sources  of  supply  developed  competition ;  but  before  many 
of  the   competing  companies  had  gained  commercial  experience 

*  In  Berlin,  Germany,  the  requirement  for  rock  asphalt  pavement  is  15  mm. 
(0.  6  inch)  under  a  straight  edge  1  meter  (3.28  feet)  long. 


ART.  2.]  SHEET   ASPHALT   PAVEMENTS.  433 

and  technical  knowledge  to  enable  them  to  compete  upon  an  equal 
footing  with  the  parent  company  and  its  auxiliaries,  a  new  com- 
bination, or  "trust/'  was  formed.  Consequently  during  but  little, 
if  any,  of  the  history  of  the  asphalt  paving  industry  in  this  country 
has  the  unfettered  law  of  supply  and  demand  acted  to  establish 
prices. 

Another  reason  why  current  prices  for  asphalt  pavements  are 
less  instructive  than  those  for  other  forms  is  that  it  is  customary  to 
include  in  the  contract  price  of  asphalt  pavement  the  maintenance 
for  a  term  of  years,  varying  from  5  to  15;  while  maintenance  is 
usually  not  so  included  with  other  forms  of  pavements.  The  pro- 
portion of  the  original  contract  price  required  for  maintenance 
will  vary  with  the  local  circumstances,  particularly  with  the  climate, 
the  amount  and  the  nature  of  the  traffic,  the  width  of  the  street,  and 
the  presence  or  absence  of  street-car  tracks. 

667.  Cost  of  Asphalt.  The  real  value  of  asphalt  for  paving 
purposes  depends  upon  the  per  cent  of  contained  bitumen  soluble 
in  carbon  bisulphide;  and  consequently  when  a  price  of  asphalt  is 
given  a  statement  should  also  be  made  of  the  per  cent  of  soluble 
bitumen  present.  In  the  days  of  freest  competition,  the  price  of 
Trinidad  asphalt  in  the  cities  on  the  Atlantic  coast  of  the  United 
States  governed  the  price  of  all  asphalts  for  that  part  of  the  country 
east  of  the  Rocky  Mountains. 

The  estimated  cost  of  Trinidad  asphalt  in  New  York  City  is 

as  follows:  * 

Digging,  transferring  to  vessel,  and  loading,  per  long  ton $1 .60 

Royalty  on  asphalt  from  government  lands,  per  long  ton .40 

Export  dut}r,  per  long  ton 1 .  20 

Freight  and  insurance  to  New  York 2 .  00 

Unloading .50 

Cost  of  crude  asphalt,  per  long  ton $5 .  70 

Cost  of  refining,  allowing  30  per  cent  loss 2 .  50 

Cost  of  about  1,568  pounds  of  refined  asphalt $8 .  20 

Cost  of  refined  asphalt  per  short  ton $10.49 

The  lowest  market  quotations  for  refined  Trinidad  asphalt, 
which  contains  about  53  per  cent  of  bitumen  soluble  in  carbon 
bisulphide    (Table    40,    page    393),    of    New    York    City    have 

*  Report  of  Commissioners  of  Account  of  the  City  of  New  York  on  Asphalt  Pav- 
ing, May  9,  1899,  p.  33-37. 


434  ASPHALT   PAVEMENTS.  fCHAP.   XIII. 

been  $30  to  $35  for  1,880  pounds  net,  or  about  $35  to  $42  per 
long  ton  net.  It  is  claimed  *  that  the  selling  price  in  European 
sea  ports  for  a  number  of  years  past  Las  been  about  as 
follows:  crude  $10.34,  refined  $17.54,  per  long  ton,  net.  It  is 
also  claimed  f  that  the  above  estimates  are  corroborated  by  the 
prospectus  issued  by  the  London  Company  and  verified  by  the 
certificate  of  Chartered  Accountants.  The  difference  in  price 
between  the  two  sides  of  the  Atlantic  is  probably  due  to  the  fact 
that  in  Europe  there  is  less  demand  for  asphalt  pavements 
(see  §  597)  and  more  competition  in  rock  asphalts;  while  in  this 
country  there  is,  or  at  least  was  formerly,  a  general  belief  that 
Trinidad  lake  asphalt  makes  a  better  pavement  than  asphalt  from 
other  sources. 

668.  Cost  of  Construction.  Asphalt  pavements  are  compar- 
atively expensive,  since  the  tools  and  machinery  employed  in 
mixing  and  laying  the  asphalt  are  costly  and  subject  to  large 
depreciation  whether  idle  or  in  use,  and  also  since  the  business 
requires  a  considerable  proportion  of  skilled  labor.  One  of  the 
peculiarities  of  the  business  is  the  disproportionate  amount  of  cap- 
ital invented  in  the  plant  compared  with  the  business  done,  often 
an  expensive  plant  being  maintained  in  a  city  for  one  or  more 
years  without  laying  any  pavement  or  at  most  only  a  comparatively 
small  amount.  Another  peculiarity  is  that  the  working  season 
is  short,  extending  only  from,  say,  the  first  of  May  to  the  first 
of  November;  and  as  expert  superintendents  and  foremen  are 
indispensable,  it  is  necessary  to  employ  this  skilled  labor  by 
the  year. 

The  estimate  of  the  cost  of  laying  an  asphalt  pavement 
shown  in  Table  43  was  prepared  for  this  volume  by  a  man 
of  acknowledged  ability  and  unquestioned  integrity,  who  has 
had  15  to  20  years'  experience  in  the  administration  of  asphalt 
paving  business  in  various  cities,  but  who  at  the  time  of  making 
this  estimate  had  no  financial  or  other  interest  in  such  matters. 
The  estimate  is  for  a  city  in  which  20,000  square  yards  are  laid  in 
one  year. 

*  Beport  of  Commissioners  of  Account  of  the  City  of  New  York  on  Asphalt 
Paving,  May  9,  1899,  p.  34. 
fibid.,  p.  36-37. 


ART.   2]  SHEET    ASPHALT    PAVEMENTS.  435 

TABLE  43. 
Estimated  Cost  of  Laying  Asphalt  Pavement. 
Plant  and  Capital  Charges: 

Interest  on  cost  of  fixed  plant,— 5%  of  $13,500 $675.00 

Interest  on  cost  of  rollers,  tools,  etc.,— 5%  of  $3,000..  150.00 

Taxes— 2%  of  $10,000 200.00 

Insurance,— 4%  of  $10,000 400.00 

Depreciation,— 8%  of  $16,500 1  320.00 

Rental  or  interest  on  real  estate,— 7%  of  $4,000 280 .  00 

Interest  for  6  mo.  on  working  capital,— 5%  of  $6,000.  150.00 

Current  repairs 300 .  00 

Watchman  for  1  year 300.00 

Total  for  20,000  sq.  yds $3  775.00 

For  1  square  yard 0. 189 

Local  Management  and  Clerical  Expenses: 

Rent  of  office  1  year $400.00 

Telephone,  light,  water,  etc 100.00 

Salary  of  Superintendent  for  6  months 1  000 .  00 

Cashier  in  charge  of  office — 6  months 600 .  00 

Clerks,  time  keepers,  etc. — 3  months 360 .  00 

Proportionate  part  of  winter  pay  roll 750.00 

Total  for  20  000  sq.  yds 3  210.00 

For  1  square  yard 0.16 

General  Officers  and  Offices: 

Laboratory  and  general  expenses 0.20 

Expense  Securing  Contracts: 

Agent's  commission,  legal  and  traveling  expenses,  etc 0. 12 

Material  and  Labor  per  Sq.  Yd.: 

Subgrade, — 0.25  cu.  yd.  grading,  rolling,  etc 125 

Foundation,— 6  inches  of  concrete  (1  N.  C.  :  2  S.  :  4  B.  S.).     .48 
Binder, — 1  inch  complete 17 

Wearing  coat, — 2  inches: 

40  lb.  refined  Trinidad  asphalt  at  $30  per  ton 60 

0.75  gal.  residuum  oil  at  6c 045 

0.083  cu.  yd.  sand  at  $1.20 10 

16  lb.  pulverized  limestone  at  $3.50  per  ton 028 

Fuel  used  at  plant 029 

Oil,  waste,  and  sundries 002 

Labor  at  plant 073' 

Hauling  material  to  street 03 

Laying  and  rolling 075 

Total  for  materials  and  labor 1 .  757 

Cost  of  Guarantee: 

5  years  at  21  cents  per  year .125 

Total  cost  of  pavement,  per  sq.  yd $2 . 551 


436  ASPHALT    PAVEMENTS.  [CHAP.  XIII. 

669.  Of  course  the  cost  will  vary  slightly  in  different  cities; 
but  the  estimates  in  Table  43  are  intended  to  be  fair  averages. 
The  figures  for  cost  of  materials  and  labor  are  averages  of  data 
from  actual  work,  and  include  transportation  and  loss  by  tare, waste, 
etc.  For  example,  while  the  actual  quantity  of  asphalt  in  a  square 
yard  of  pavement  is  about  32  pounds,  40  pounds  must  be  purchased, 
since  the  tare  (weight  of  barrels  and  of  asphalt  adhering  to  them) 
is  12 J  per  cent;  and  the  loss  through  evaporation,  sedimentation 
skimming  and  waste  is  7  or  8  per  cent  more. 

No':  infrequently  in  recent  years  have  prices  been  obtained 
considerably  less  than  the  estimate  in  Table  43.  For  example, 
during  the  years  1895-98,  when  the  competition  between  the  vari- 
ous asphalt  paving  contractors  was  very  sharp,  bids  were  received 
in  several  widely  separated  cities  as  low  as  $1.40  to  $1.50  for  nom- 
inally the  same  pavement  as  in  Table  43.  It  should  be  stated, 
however,  that  the  above  were  years  of  great  industrial  depression, 
and  consequently  wages  were  low  and  there  was  less  paving  in 
progress  than  usual.  The  asphalt  paving  contractors  explain 
this  discrepancy  by  saying  that  their  plant  and  organization  sub- 
ject them  to  large  fixed  charges  whether  or  not  they  do  any  work, 
and  that  therefore  it  is  better  to  keep  the  men  and  plants  at  work 
at  any  price  that  leaves  a  little  margin  above  actual  cost  of  ma- 
terials and  labor.  The  asphalt  paving  contractors  claim  that  con- 
tracts have  sometimes  been  taken  at  a  loss  to  drive  competitors 
from  the  field;  and  also  claim  that  many  of  the  smaller  asphalt 
companies  actually  lost  money  in  their  business,  and  continued  in 
the  field  only  because  they  hoped  to  compel  their  more  successful 
competitors  to  buy  them  out.  It  is  further  claimed  that  if  the 
contractor  is  less  careful  of  the  quality  of  his  work,  the  price  can 
be  materially  reduced,  since  a  less  expensive  plant  may  be  em- 
ployed and  no  permanent  organization  would  be  maintained.  The 
estimates  in  Table  43  contemplate  first-class  work  in  every  partic- 
ular; but  of  course  if  a  lower  grade  is  sufficient,  the  price  may  be 
lessened  by  reducing  the  quantity  and  quality  of  the  concrete, 
the  thickness  and  quality  of  the  wearing  course,  the  amount  of 
rolling,  the  care  employed  in  forming  a  true  surface,  etc.  Table  44, 
page  438,  shows  the  average  prices  paid  in  forty-five  cities  during 
the  year  1900,  and  also  gives  some  of  the  details  concerning  tho 


ART.   2.]  SHEET   ASPHALT   PAVEMENTS.  437 

method  of  construction  and  the  cost  of  materials,  labor,  etc.  No- 
tice that,  the  prices  in  Table  44  do  not  include  grading,  i.  e.,  include 
only  the  concrete  base,  the  binder,  the  wearing  coat,  and  a  5- 
year  or  a  10-year  guarantee;  while  the  cost  of  the  corresponding 
items  in  Table  43  is  $2.43  for  a  5-year  guarantee  and  $2.55  for  a 
10-year  guarantee.  In  Washington,  D.  C,  the  maximum  price 
is  limited  by  act  of  Congress  to  $1.80  per  square  yard  for  a  l}-inch 
wearing  coat,  a  lj-inch  binder  course,  a  6-inch  concrete  base 
(1  N.  C. :  2  S. :  5  B.  S.),  and  a  5-year  guarantee. 

670.  Cost  of  Maintenance.  The  cost  of  maintenance  will  vary 
with  the  original  quality  of  the  pavement,  its  age,  the  amount  and 
nature  of  the  traffic — the  cost  under  either  very  heavy  or  very 
light  traffic  being  greater  than  that  under  moderate  travel, — the 
width  of  the  street,  the  presence  or  absence  of  street-car,  tracks, 
the  frequency  with  which  the  pavement  is  cleaned  and  sprinkled, 
the  climate,  etc.  Owing  to  the  marked  influence  of  some  of  these 
elements,  and  to  the  usual  lack  of  definite  data  concerning  the  most 
of  them,  it  is  impossible  to  give  data  of  any  considerable  general 
value. 

Table  45,  page  440,  gives  the  cost  of  repairs  of  asphalt  pave- 
ments in  Buffalo,  N.  Y.,  a  city  that  until  recently  had  more  such 
pavements'than  any  other  city  in  the  world.  An  inspection  of  the 
table  shows  a  marked  variation  in  the  cost  of  repairs  from  year  to 
year.  The  results  for  pavements  laid  in  1883,  1885  and  1886  are 
abnormally  high,  a  fact  which  shows  that  considerable  poor  work 
was  done  during  those  years. 

Table  46,  page  441,  gives  data  on  the  cost  of  repairs  of  asphalt 
pavements  in  Buffalo  on  residence  and  business  streets  with  and 
without  street-car  tracks.  Notice  that  the  cost  on  business  streets 
increases  each  successive  year,  while  that  for  residence  streets  as  a 
rule  decreases  after  the  sixth  year.  The  first  result  is  what  would 
be  expected;  but  no  satisfactory  explanation  has  been  found  for 
the  anomaly  of  the  second  result.  Notice  also  that  the  cost  on 
residence  streets  is  more  with  street-car  tracks  than  without  them, 
a  condition  which  is  contrary  to  ordinary  experience.  Both  of  the 
above  anomalous  results  are  doubtless  due  to  poor  work  or  to  excess- 
ive travel  on  one  or  more  of  the  streets. 


4-38 


ASPHALT    PAVEMENTS. 


[CHAP.   XIII. 


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ART.  2.] 


SHEET  ASPHALT  PAVEMENTS. 


439 


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440 


ASPHALT   PAVEMENTS. 


[CHAP.  XIII. 


671.  Table  47,  page  442,  shows  the  cost  of  maintenance  of  the 
asphalt  pavements  in  Washington,  D.  C.  These  results  are  com- 
piled from  Table  D,  Asphalt  Pavements  on  6-inch  Hydraulic  Base, 
in  the  Report  of  the  Operations  of  the  Engineering  Department  of 
the  District  of  Columbia  for  the  year  ending  June  30,  1900.     The 

TABLE  45. 
Cost  of  Maintenance  of  Asphalt  Pavements  in  Buffalo,  N.  Y.,  from 

1885  to  1897.* 


Main- 

Cost of 

Cost  of 

tained 

Area  of 

Pavement  on 

Streets 

Repaired. 

Repairs 

Year 
Laid. 

No.  of 

Length 

Total  Area  of 

Repairs 

After 

per  Year 

Streets 

of  Guar- 

Pavement 

per  Sq. 

Expira- 

per Sq. 

Paved. 

antee. 

Maintained. 

Yd.  per 
Annum. 

tion  of 
Guar- 

Yd. of 
such 

antee. 

Street  s. 

Years. 

Sq.  Yd. 

Cents. 

Years. 

Sq.  Yd. 

Cents. 

1878 

1 

5 

9  286 

0.60 

9 

9  286 

0.60 

1879 

1 

5 

7  264 

4.15 

13 

7  264 

4.15 

1880 

1 

5 

3  755 

2.25 

12 

3  019 

2.80 

1881 

1 

5 

8  876 

2.00 

11 

8  876 

2.00 

1882 

2 

5 

25  501 

2.19 

10 

25  501 

2.19 

1883 

3 

5 

35  815 

6.91 

9 

35  815 

6.91 

1884 

8 

8 

79  774 

5.02 

5 

79  744 

5.02 

1885 

15 

5 

113  498 

7.49 

7 

110  418 

7.49 

1886 

28 

5 

236  001 

7.90 

6 

203  371 

9-.  16 

1887 

14 

5 

126  490 

5.06 

5 

122  780 

5.21 

1888 

14 

5 

201  668 

3.91 

4 

201  668 

3.91 

1889 

40 

5 

249  333 

2.24 

3 

244  084 

2.29 

1890 

51 

5 

370  125 

2.16 

2 

341  875 

2.34 

1891 

43 

5 

419  579 

1.02 

1 

323  743 

1.32 

♦Compiled  from  au  article  on  Repairs  of  Asphalt  Pavements  in  Buffalo,  N.  Y., 
by  Edward  B.  Guthrie,  Chief  Engineer,  in  Proc.  Amer.  Soc.  of  Municipal  Improve- 
ments, Vol.  5,  p.  123-29. 

original  table  is  arranged  geographically  by  streets  and  gives  the 
cost  of  repairs  for  each  contract  for  each  year  after  the  expiration 
of  the  5-year  guarantee  period.  The  results  in  Table  47  are  the 
means  of  the  annual  cost  of  repairs  for  the  several  contracts;  and 
take  no  account  of  the  different  areas  covered  by  the  different  con- 
tracts; but  the  resulting  error  is  not  material.  The  most  con- 
spicuous feature  of  the  table  is  that  the  pavements  laid  in  1878  cost 
much  more  for  maintenance  than  those  laid  later,  after  the  best 
method  of  doing  the  work  was  better  understood. 

Table  47  suggests  comparisons  with  Table  45;  but  it  is  impos- 
sible to  draw  any  reliable  conclusions,  since  nothing  is  known  con- 


ART.  2.] 


SHEET  ASPHALT  PAVEMEKTS. 


441 


cerning  the  relative  amount  of  traffic  per  unit  of  width,  and  also 
since  nothing  is  known  about  the  relative  excellence  of  the  state 
of  repairs  in  the  two  cities.  In  each  case  there  is  a  considerable 
variation  in  the  results  from  year  to  year,  depending  upon  the 
number  of  streets  that  were  re-surfaced  that  particular  year. 

TABLE  46. 


Cost  of  Maintenance  of  Asphalt  Pavements  in  Buffalo,  N.  Y. 
Square  Yard  per  Annum  from  1885  to  1897.* 


PER 


Business  Streets. 

Residence  Streets. 

Years 

After 

Expiration 

of  Guar- 

With Car  Tracks. 

Without  Car 
Tracks. 

With  Car  Tracks. 

Without  Car 
Tracks. 

antee. 

No.  of 

Streets. 

Cost  per 
Sq.  Yd. 

No.  of 

Streets. 

Cost  per 
Sq.  Yd. 

No.  of 

Streets. 

Cost  per 
Sq.  Yd. 

No.  of 
Streets. 

Cost  per 
Sq.  Yd. 

1 

20 

Cents. 

5.1 

12 

Cents. 

3.2 

6 

Cents. 
4.0 

34 

Cents. 

1.3 

2 

21 

11.8 

16 

12.4 

8 

5.5 

57 

2.9 

3 

15 

11.4 

12 

6.7 

8 

4.3 

50 

4.5 

4 

11 

15.7 

9 

11.7 

7 

4.8 

43 

7.5 

5 

8 

16.7 

7 

13.8 

9 

11.9 

39 

6.2 

6 

6 

17.2 

5 

13.1 

5 

6.3 

26 

4.9 

7 

1 

23.9 

2 

18.0 

3 

6.6 

13 

7.2 

8 

1 

1.2 

6 
6 
4 
2 
1 
1 

4.7 

9 

2.9 

10 

1 
1 
1 

2.5 
4.7 
4.3 

2.7 

11 

3.4 

12 

3.7 

13 

10.6 

Average.. 

14.8 

11.2 

4.7 

4.8 

672.  In  New  York  city,  the  average  difference  in  contract  price 
for  a  15-year  and  for  a  5-year  maintenance  for  the  three  years  pre- 
ceding 1894  was  $0,608,  or  6.08  cents  per  square  yard  per  annum, 
and  for  the  three  years  following  1894  was  5.82  cents  per  square 
yard  per  annum.  The  area  of  pavements  included  was  quite  large, 
and  hence  the  result  is  fairly  representative.! 

673.  In  Berlin,  Germany,  the  contract  price  for  the  mainte- 
nance of  the  great  majority  of  the  asphalt  pavements  is  0.75  marks 


♦Repairs  of  Asphalt  Pavements  in  Buffalo,  N.  Y.,  by  Edward  B.  Guthrie,  Chief 
Engineer,  in  Proc.  Amer.  Soc.  of  Municipal  Improvements,  Vol.  5,  p.  123-29. 

+  E.  P.  North,  Consulting  Engineer  to  the  Commissioner  of  Public  Works  of  the 
City  of  New  York,  in  Engineering  Record,  Vol.  44,  p.  418. 


442 


ASPHALT    PAVEMENTS. 


[CHAP.   XIII. 


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ART.  2.] 


SHEET   ASPHALT    PAVEMENTS. 


44? 


per  square  meter  (about  15  cents  per  square  yard),  provided  the 
total  amount  of  repairs  in  one  year  is  not  more  than  5,000  square 
meters  (6,000  sq.  yd.);  if  the  total  repairs  amount  to  more  than 
5,000  square  meters  in  a  year,  the  price  is  0.50  marks  a  square 
meter  (about.  10  cents  per  square  yard). 

It  is  often  stated  that  the  cost  of  maintaining  asphalt  pave- 
ments in  Europe  is  from  10  to  25  cents  per  square  yard  per  annum, 
an  amount  which  is  considerably  higher  than  the  average  for 
America;  but  all  such  data  are  indefinite  and  unreliable,  since  noth- 
ing is  stated  concerning  the  traffic  and  the  state  of  maintenance. 
As  a  rule,  the  streets  of  Europe  are  narrower  and  the  traffic  per 
foot  of  width  is  heavier  than  in  America ;  and  therefore  it  is  prob- 
able that  the  cost  of  maintenance  in  Europe  is  higher  than  in  this 
country. 

674.  Prices  of  Repairs.  Table  48  shows  the  prices  paid  for 
sundry  repairs  to  asphalt  pavements  in  Buffalo,  N.  Y.;  for  a  num- 
ber of  years. 

TABLE  48. 
Contract  Prices  for  Repair  of  Asphalt  Pavements  in  Buffalo,  N.  Y* 


Ref. 

Items. 

During  the  Year. 

No. 

1896. 

1897. 

1898. 

1899. 

1900. 

1 

Average  for  new  pavement,  per 
sq.  vd 

$2.97f 

2.25 
1.35 

.88 
.02 

.035 

.17 

$2.55f 

2.39 

1.46 

.98 

.02 

.04 

.19 

|2.17f 

1.90 

1.05 

.64 

.01 

.02 

.15 

$2.60J 

2.39 

1.46 

.98 

.02 

.04 

.19 

$2.20§ 
2.43 

2 

Replacing  concrete,  binder,  and 

3 

4 

New  asphalt  surface,  per  sq  yd. 
Skimming  per  sq.  vd 

1.53 
1.01 

5 
6 

Filling  cracks,  per  fin.  ft 

Painting  gutters,  1  ft.  wide,  per 
lin.  ft 

.02 
.04 

7 

Replacing    stone    toothing,    per 
lin.  ft 

.19 

*  Annual  Report  of  Board   of  Public  Works  for  1900,  p.  69,  and  private  cor- 
respondence. 

f  Including  excavation,  curb,  drain  tile,  and  a  5-year  guarantee. 
I  Including  excavation,  curb,  drain  tile,  and  a  10-year  guarantee. 
§  Including  only  concrete,  binder,  topping,  and  a  10-year  guarantee. 

In  Washington,  D.  C,  the  cost  of  small  and  irregular  patches 
is  based  upon  the  volume  of  binder  and  of  mixture  for  the  wearing 


444 


ASPHALT   PAVEMENTS. 


[CHAP.   XIII. 


coat  used  in  making  the  repairs.  The  prices  in  the  contract 
for  repairs  for  the  three  years  beginning  July  1,  1900,  are  as 
follows :  * 

"1.  Laying  standard  asphalt  pavement  (2 J 
inches  of  asphalt  and  2  inches  of 
binder — before  compression)  on  a  6-inch 
hydraulic  concrete  base  (1  N.  C. :  2  S.: 
5  S.) $1.77 1  per  sq.  yd 

2.  Laying    standard    asphalt    surface     (2J 

inches  before  compression 0.91       "     "     " 

3.  Laying  standard  asphalt  surface  (2  inches 

before  compression) 0.80      "     "     " 

4.  Laying  standard  asphalt  surface  (measured 

in  cart) 0.60  per  cu.  ft. 

5.  Laying  asphalt  binder  (measured  in  cart)     0.31    "     "     " 

6.  Laying  standard  asphalt  surface  by  the 

burner  method  I  (measured  in  cart)...     1.00    "     u     " 

No  price  is  stated  for  painting  the  gutters,  since  the  standard  for 
new  work  requires  brick  gutters  2  feet  wide,  and  the  repairs  to  old 
asphalt  gutters  is  made  the  same  as  in  the  remainder  of  the  road- 
way. The  placing  of  stone  toothing  along  street-car  tracks  is 
done  by  the  railroad  company." 

675.  Cross  Section  of  Asphalt  Pavement.    Fig.  119  and 


Asbhalt  limrBinder//n 


*,  Concrete  Sin,  a 


Fig.  119.— Sheet  Asphalt  Pavement. 


*■  ll  [r  -  A  *phgk  2in  .-Binder /in 

^  I?-  -*  *  Cnncrere  6/r?  .*£? 
\\\-*.*//£  fOBF*  Unf 


Fig   120.— Sheet  Asphalt  Pavement. 


120  show   the    typical    cross    section   of   an    asphalt   pavement. 
Asphalt  is  frequently  laid  upon  an  old  cobble-stone  pavement,  or 


*  By  courtesy  of  Maj.  John  Biddle,  IT.  S.  A.,  Engineer  Commissioner  of  D.  C. 
f  The  contract  price  for  entirely  new  work  is  $1.72. 

*  Skimming— see  §  660. 


ART.   2.]  SHEET  ASPHALT   PAVEMENTS.  445 

upon  one  of  stone  block  or  brick,  and  occasionally  upon  a  macadam 
pavement. 

676.  MAXIMUM  GRADES  FOR  ASPHALT  PAVEMENTS.  Until 
within  a  few  years,  it  has  been  assumed  that  the  maximum  per- 
missible grade  for  a  sheet  asphalt  pavement  was  2  or  2 J  per  cent ; 
but  experience  has  shown  that  this  limit  is  too  low.  It  is  now  gen- 
erally conceded  that  sheet  asphalt  may  be  laid  on  grades  of  5  or 
6  per  cent,  particularly  in  residence  streets — where  a  clean,  smooth, 
noiseless  pavement  is  specially  desirable,  and  where  there  is  usu- 
ally no  great  amount  of  traffic.  With  a  5  or  6  per  cent  grade,  there 
may  be  a  few  days  each  year  when  the  pavement  is  icy  and  too 
slippery  for  either  comfortable  or  safe  use.  In  New  York  city,  on 
Si  street  having  a  6  per  cent  grade  paved  with  asphalt  on  the  sides 
and  granite  in  the  center,  the  traffic  as  a  rule  seeks  the  asphalt 
rather  than  take  the  granite,  and  in  the  same  city  traffic  has  de- 
serted one  street  having  a  5  per  cent  grade  paved  with  granite  for 
another  having  a  6  per  cent  grade  paved  with  asphalt.  A  number 
•of  cities  have  sheet  asphalt  pavements  upon  a  7  per  cent  grade,  as, 
for  example,  Peoria,  111.,  Grand  Rapids,  Mich.,  Syracuse,  N.  Y., 
Troy,  N.  Y.;  and  Omaha,  Neb.,  and  St.  Joseph,  Mo.,  have  asphalt 
pavements  on  an  8  per  cent  grade.  Scran  ton,  Pa.,  has  a  short 
piece  of  asphalt  on  a  13  per  cent  grade,  San  Francisco,  Cal.,  a  piece 
on  a  16  per  cent  grade,  and  Pittsburg,  Pa.,  one  on  a  17  per  cent 
grade. 

677.  Merits  and  Defects  of  Sheet  Asphalt  Pave- 
ments. The  advantages  possessed  by  monolithic  asphalt  pave- 
ments constructed  as  described  above  are:  (1)  they  produce  nei- 
ther dust  nor  mud;  (2)  they  are  comparatively  noiseless,  except 
for  the  clicking  of  the  horses'  shoes;  (3)  they  do  not  absorb 
or  retain  noxious  liquids,  but  facilitate  their  prompt  discharge 
into  the  gutters  and  storm-water  sewers;  (4)  they  reduce 
the  force  of  traction  to  a  moderate  amount  (see  Table  8, 
page  29);  and  (5)  they  afford  a  reasonably  good  foot-hold  for 
horses.* 

The  defects  of  sheet  asphalt  pavements  are:  1.  The  first  cost 

♦For  a  discussion  of  the  limiting  grades  of  sheet  asphalt  pavements,  see  the 
preceding  paragraph. 


446  ASPHALT    PAVEMENTS.  [CHAP.   XIII, 

is  comparatively  great;  2,  the  cost  of  maintenance  is  large;  and 
3,  such  pavements  are  generally  considered  too  smooth  for  steep 
grades  (§  676). 

678.  For  a  discussion  of  the  relative  merits  of  the  different 
pavements,  see  Chapter  XVIII. 

Art.  3.     Rock  Asphalt  Pavements. 

679.  This  form  of  pavement  is  made  by  crushing  bituminous 
limestone  or  sandstone,  and  laying  it  while  hot  upon  a  concrete 
foundation.  In  Europe  this  is  the  common  form;  and  when  the 
term  asphalt  pavement  is  used  there,  this  kind  is  intended. 

Rock  asphalt  pavements  have  been  laid  only  to  a  comparatively 
small  extent  in  America,  it  being  claimed  that  there  are  only  about 
75,000  square  yards  now  in  use  in  the  United  States  outside  of  Cali- 
fornia. Rock  asphalt  pavements  have  been  used  in  a  small  way 
in  California  for  many  years,  and  San  Francisco,  Los  Angeles,  and 
other  cities  now  have  several  miles  of  such  pavements.  Appar- 
ently both  asphaltic  limestones  and  sandstones  are  used  in  Cali- 
fornia; but  the  most  of  the  so-called  rock  asphalts  used  for.  paving 
purposes  are  asphaltic  limestones. 

A  bituminous  limestone  to  be  suitable  for  paving  purposes 
should  be  as  coarse-grained  as  possible,  should  contain  between  9 
and  10  per  cent  of  bitumen  soluble  in  carbon  bisulphide,  and 
should  contain  very  little  matter  volatile  below  400°  F.  Often  one 
or  more  natural  rocks  are  mixed  to  secure  the  proper  proportion 
of  bitumen;  and  sometimes  a  natural  asphalt  is  added  to  the  nat- 
ural rock  to  increase  the  proportion  of  bitumen. 

680.  CONSTRUCTION.  The  asphaltic  rock  is  quarried,  and 
then  crushed  to  about  egg  size  by  toothed  rollers.  These  pieces 
are  first  reduced  to  powder  and  then  sifted  to  uniform  fineness. 
The  powder  is  dropped  through  a  hopper  into  a  revolving  cylinder 
like  a  coffee  roaster,  which  is  about  6i  feet  in  diameter,  and  is  sur- 
rounded by  a  chamber  the  air  in  which  is  heated  by  a  movable 
furnace  placed  just  below  it.  The  cylinder  itself  revolves  and, 
since  it  is  provided  with  blades  arranged  in  screw  form,  the  pow- 
dered rock  is  well  mixed  with  hot  air  and  is  thus  thoroughly 
heated  to  a  temperature  between  300°  and  350°  F.  Specifications 
frequently  permit  the  rock  asphalt  to  be  heated  to  but  200°  to  250°  F. 


ART.  4.]  ASPHALT   BLOCK   PAVEMENT.  447 

When  the  powder  is  hot  enough,  the  furnace  is  removed  from  under 
the  heater  and  a  cart  replaces  it,  into  which  the  asphalt  powder  is 
discharged  and  hauled  upon  the  work.  The  powder  will  retain  its 
heat  for  several  hours  and  so  admits  of  being  carted  long  distances 
without  losing  its  heat,  thus  doing  away  with  the  necessity  of 
having  roasters  at  the  point  where  the  surface  is  to  be  laid,  as  was 
at  one  time  the  practice.  For  the  best  results,  the  mixture  should 
be  delivered  upon  the  street  at  a  temperature  of  not  less  than 
250°  F.,  although  specifications  sometimes  permit  a  temperature 
of  but  190°  F. 

The  heated  powder  is  spread  upon  the  concrete  base  to  a  uni- 
form thickness  about  40  per  cent  greater  than  that  required  for  the 
finished  pavement.  This  must  be  done  with  great  care  in  order 
that  the  material,  which  while  hot  has  a  great  tendency  to  consoli- 
date, may  not  be  denser  in  one  spot  than  another.  The  material 
is  compacted  by  rolling  and  ramming  in  much  the  same  way  as  is 
described  for  the  artificial  asphaltic  paving  compound  (see  §  629), 
except  that  as  a  rule  the  natural  rock  asphalt  is  not  consolidated 
to  so  great  an  extent  as  is  customary  in  laying  the  artificial  mix- 
ture. The  evidence  of  this  is  that  a  rock  asphalt  pavement  will 
continue  to  shrink  in  thickness  under  traffic  for  a  year  or  two, 
while  the  artificial  mixture  shrinks  but  little,  if  any,  after  com- 
pletion. 

681.  The  general  appearance  of  the  completed  pavement  is 
much  the  same  as  that  of  the  pavement  made  of  the  artificial  mix- 
ture, except  that  the  European  rock  pavements  are  lighter  in 
color.  The  claim  is  that  European  natural  rock  asphalt  pave- 
ments are  more  slippery  and  less  susceptible  to  changes  in  tempera- 
ture than  are  American  artificial  asphalt  pavements. 

Not  infrequently  the  term  rock  asphalt  pavement  is  inappro- 
priately applied  to  a  pavement  made  of  an  artificial  mixture  of 
sand  and  of  asphalt  extracted  from  a  natural  rock. 

Art.  4.     Asphalt  Block  Pavement. 

682.  There  are  two  general  forms  of  asphalt  pavements,  the 
sheet  or  monolithic  and  the  block.  The  first  has  been  fully  de- 
scribed in  the  two  preceding  sections.  The  latter  is  constructed 
by  first  molding  rectangular  blocks  composed  of  asphaltic  cement 


448  ASPHALT    PAVEMENTS.  [CHAP.   XIII. 

and  crushed  stone,  and  then  placing  these  blocks  side  by  side  upon 
a  gravel  or  concrete  foundation.  Asphalt  paving  blocks  were  first 
made  in  San  Francisco  in  1869;  and  at  present  there  are  in  this 
country  about  1,500,000  square  yards  of  asphalt  block  pavement 
or  about  one  twentieth  as  much  as  sheet  asphalt.  This  form  of 
pavement  has  been  more  largely  used  in  Washington,  D.  C,  than 
any  other  place;  but  comparatively  large  areas  have  been  laid  in 
Baltimore  and  in  New  York  city. 

683.  THE  BLOCKS.  At  first  crushed  limestone  was  used,  but 
now  the  blocks  are  made  with  crushed  trap,  granite,  or  gneiss. 
The  asphaltic  cement  is  mixed  substantially  as  for  sheet  pavements. 
The  proportions  employed  in  making  the  blocks  vary  slightly  with 
the  climate  and  considerably  with  the  fineness  of  the  crushed  stone, 
but  are  about  as  follows: 

'    Asphaltic  Cement  8  to  12  per  cent 

Limestone  Dust  8  to  10  per  cent 

Crushed  Stone  84  to  78  per  cent. 

Since  the  blocks  contain  larger  fragments  than  sheet  pavements, 
they  contain  a  smaller  per  cent  of  voids,  and  hence  can  be  made 
with  a  slightly  smaller  per  cent  of  asphaltic  cement. 

The  ingredients  are  mixed  and  heated  about  as  for  sheet  pave- 
ments, and  are  then  moulded  while  hot  under  heavy  pressure. 
Formerly  the  blocks  were  made  5"  X  12"  X  4"  deep;  but  now  they 
are  made  4"  X  12"  X  3"  deep,  and  also  5"  X  12"  X  3"  deep. 
Tiles  are  made  8"  X  8"  X  2\"  deep,  and  also  with  a  hexagonal  top 
surface  having  the  same  area  as  the  square  tile.  The  blocks  are 
used  for  carriage  ways,  and  the  tiles  for  foot  ways.  The  weight 
of  the  compressed  blocks  is  about  165  pounds  per  cubic  foot.  After 
being  compressed  the  blocks  are  cooled  by  being  placed  in  water, 
and  then  they  are  ready  for  laying. 

Fig.  121  shows  a  perspective  view  and  a  cross  section  of  a  car- 
riage way  and  a  foot  way  paved  with  asphalt  blocks. 

684.  Cost  of  Blocks.  The  cost  of  asphalt  blocks  varies  in  differ- 
ent cities,  being  in  1902  in  Toledo,  0.,  $60.00  per  1,000  for  blocks 
4"  X  12"  on  top  and  4"  deep,  or  about  $1.60  per  square  yard;  and 
in  New  York  city,  $50.00  per  1,000  for  blocks  5"  X  12"  on  the  top 


ART.  4.] 


ASPHALT    BLOCK    PAVEMEKT. 


449 


face  and  3"  deep,  or  about  $1.10  per  square  yard.     The  cost  of  the 
labor  to  lay  varies  from  8  to  10  cents  per  square  yard. 


Fig.  191.— Asphalt  Block  Pavement. 

685.  Specifications  for  Laying.  Below  are  the  specifica- 
tions employed  for  asphalt  block  pavements  on  carriage  ways,  in 
the  City  of  Washington.* 

686.  Road-bed.  The  space  over  which  the  pavement  is  to  be  laid  hav- 
ing been  excavated  to  the  proper  depth  below  the  surface  of  the  pave- 
ment when  completed,  any  objectionable  or  unsuitable  matter  below  the 
bed  will  be  wholly  removed,  and  the  space  filled  with  good  gravel  or  sand 
compactly  rolled  or  rammed.  The  bed  will  be  trimmed  so  as  to  be  paiallel 
to  the  surface  of  the  pavement  when  completed,  and  the  entire  road-bed  will 
then  be  thoroughly  compacted  by  rolling  with  a  roller  weighing  at  least  ten 
tons,  or  by  thorough  ramming  at  places  which  can  not  be  reached  by  the 
roller.     No  extra  allowance  will  be  made  for  trimming  and  rolling. 

687.  Foundation.  Two  forms  of  foundation  are  used — con- 
crete and  gravel.  The  specifications  are  as  follows,  those  for  the 
concrete  being  abridged. 

688.  Concrete  Base.  This  will  be  four  inches  thick  when  compacted, 
and  will  be  made  of  broken  stone  and  gravel,  sand,  and  natural  cement  in 
such  proportions  that  the  quantity  of  gravel  will  be  equal  to  the  volume  of 
voids  in  the  broken  stone;  and  the  sand  and  the  cement,  mixed  in  the  pro- 


*  Printed  specifications  received  from  Maj.  John  Biddle,  U.  S.  A.,  Engineer  Com- 
missioner, January,  1902. 


450  ASPHALT    PAVEMENTS.  [CHAP.   XIII. 

portion  of  one  part  cement  and  two  parts  sand,  will  be  20  per  cent  in  excess 
of  the  volume  of  the  voids  in  the  combined  gravel  and  broken  stone.  Upon 
the  concrete  will  be  laid  a  course  of  fine  sharp  sand,  half  an  inch  thick,  to 
serve  as  a  bed  for  the  blocks.  Special  care  will  be  observed  to  make  the  sur- 
face of  the  sand  exactly  parallel  to  the  surface  of  the  pavement  when  com- 
pleted. 

689.  Gravel  Base.  Upon  the  road-bed  prepared  as  above  is  to  be  laid  a 
course  of  bank  gravel,  screened  from  all  pebbles  measuring  more  than  one 
and  one  half  inches  in  their  largest  dimension,  of  such  a  depth  as  to  give  five 
inches  in  thickness  when  compacted  by  rolling  and  ramming.  Upon  the 
gravel  will  be  spread  a  layer  of  fine  sharp  sand  two  inches  in  thickness,  to 
serve  as  a  bed  for  the  blocks.  Special  care  will  be  observed  to  make  the 
surface  of  the  sand  exactly  parallel  to  the  surface  of  the  pavement  when  com- 
pleted. 

690.  Placing  the  Blocks.  The  blocks  will  be  4  X  12  inches  on  top 
and  five  inches  deep,*  and  a  variation  of  one  quarter  of  an  inch  from  these 
dimensions  will  be  sufficient  grounds  for  rejecting  any  block.  The  blocks 
must  be  square  and  have  sharp  corners,  and  blocks  having  chipped  or  rounded 
edges  will  be  rejected. 

The  blocks  will  be  laid  by  pavers  standing  or  kneeling  upon  the  blocks 
already  laid,  and  not  upon  the  bed  of  sand.  Each  course  will  be  formed  of 
blocks  of  a  uniform  width  and  depth.  The  blocks  will  be  laid  with  their 
length  at  right  angles  to  the  axis  of  the  street;  and  shall  be  so  laid  that  all 
longitudinal  joints  shall  be  broken  by  a  lap  of  at  least  four  inches.  Each 
course  of  blocks  will  be  driven  against  the  course  preceding  it  by  a  heavy 
wooden  maul,  in  order  to  make  the  lateral  joints  as  tight  as  possible.  The 
longitudinal  joints  will  be  closed  by  pressing  on  a  lever  inserted  at  the  end 
of  the  course  adjoining  the  curb,  and  keying  with  a  block  cut  to  the  required 
size. 

When  laid,  the  blocks  will  be  immediately  covered  with  clean,  fine  sand 
entirely  free  from  loam  or  earthy  matter,  perfectly  dry,  and  screened  through 
a  screen  having  20  meshes  to  the  inch.  The  blocks  will  then  be  rammed  by 
placing  an  iron  plate,  24  inches  by  8  inches,  and  f  inch  thick,  over  four  blocks, 
and  striking  on  the  plate  with  a  rammer  weighing  not  less  than  45  lb.  The 
ramming  will  be  continued  until  the  blocks  reach  a  firm,  unyielding  bed  and 
present  a  uniform  surface,  with  the  required  grade  and  crown.  Any  lack  of 
uniformity  of  the  surface  must  be  corrected  by  taking  up  the  blocks,  increas- 
ing or  decreasing  the  sand  bedding,  and  relaying  them.  When  the  ramming 
is  completed,  a  sufficient  amount  of  fine,  dry  sand,  as  above  described,  will 
be  spread  over  the  surface  and  swept  into  the  joints. 

The  contractor  will  be  permitted,  if  he  so  desires,  to  use  the  District  steam 
roller  No.  1  on  this  work.  The  men  and  material  for  its  use  are  to  be  sup- 
plied by  the  District,  and  are  to  be  paid  for  by  the  contractor  during  such  use. 

*  In  paving  alleys  it  is  usual  to  place  the  5  X  12-inch  face  up. 


ART.   4.]  ASPHALT   BLOCK   PAVEMENT.  451 

691.  It  is  better  to  lay  asphalt  blocks  in  hot  rather  than  in 
cool  weather.  If  the  weather  is  cool,  the  blocks  are  firm  and  do 
not  fit  closely  together;  and  consequently  the  edges  chip  or  flow 
into  the  joint,  thus  making  the  upper  surface  of  the  block  rounded 
and  the  pavement  rough  and  comparatively  noisy. 

692.  MERITS  AND  DEFECTS.  The  advantages  claimed  for  a 
pavement  of  asphalt  blocks  over  a  continuous  asphalt  sheet  are : 

1.  It  is  less  slippery,  owing  partly  to  the  joints  and  partly  to  the 
roughening  of  the  surface  due  to  the  use  of  a  hard  crushed  stone. 

2.  It  can  be  laid  on  a  steeper  grade.  3.  It  can  be  laid  in  cities 
where  there  is  no  asphalt  plant.  4.  It  can  be  taken  up  and  relaid 
by  common  labor.  5.  It  can  be  repaired  without  special  appli- 
ances or  skilled  labor.  6.  Having  numerous  joints,  it  is  free  from 
irregular  and  unsightly  contraction  cracks.  7.  It  needs  less  repair 
than  sheet  asphalt. 

The  alleged  disadvantages  of  an  asphalt  block  pavement  in 
comparison  with  a  continuous  asphalt  sheet  are:  1.  Its  first  cost 
is  more,  since  the  wearing  coat  of  the  block  pavement  is  4  inches 
thick  while  that  of  the  continuous  sheet  is  at  most  only  2\  inches. 
2/  The  edges  of  the  blocks  chip  off,  and  the  pavement  wears  rough. 

3.  It  is  slightly  more  noisy.  4.  Owing  to  its  numerous  joints,  it 
is  less  sanitary.  5.  It  is  more  expensive  to  clean.  6.  Unless 
bedded  with  unusual  care,  the  blocks  have  a  tendency  to  crack. 
7.  It  is  less  durable,  particularly  under  heavy  traffic. 

693.  COST.  The  cost  of  the  blocks  varies  from  $1.10  to  $1.60 
per  square  yard  f.o.b.  factory.  The  cost  of  laying,  sanding,  etc., 
is  about  8  cents  a  square  yard  with  common  labor  at  $1.50  for 
10  hours.  The  total  cost  of  an  asphalt  block  pavement  on  a 
foundation  of  6  inches  of  gravel  or  broken  stone,  including  the  prep- 
aration of  the  subgrade  and  the  hauling  of  the  blocks,  in  different 
cities  varies  with  freight  charges  from  the  factory,  but  is  usually 
from  $1.75  to  $2.25.  In  Washington,  where  there  is  a  block  fac- 
tory, the  price  from  1897  to  1900  was  uniformly  $1.77  per  square 
yard  on  gravel,  exclusive  of  grading.  In  1901  in  Washington,  the 
price  on  a  6-inch  hydraulic  concrete  base  was  $2.00  per  square  yard. 

694.  DURABILITY.  Apparently  there  are  no  statistics  as  to 
the  cost  of  maintenance  of  asphalt  block  pavements.     Formerly 


452  ASPHALT   PAVEMENTS.  [CHAP.   XIII. 

the  blocks  were  made  of  crushed  limestone,  and  wore  fast  and  very 
unevenly;  but  since  1893  the  blocks  have  been  made  with  harder 
stone  and  have  given  better  satisfaction. 

Art.  5.    Asphalt  Macadam. 

695.  Very  recently  it  has  been  proposed  to  use  asphalt  as  a 
binding  material  for  crushed  stone,  the  resulting  product  usually 
being  called  asphalt  macadam,  but  sometimes,  and  less  appro- 
priately, bituminous  macadam.  Doubtless  this  use  of  asphalt  has 
been  suggested  by  a  former  and  similar  use  of  coal  tar  (see  §  709). 
Asphalt  concrete  would  not  be  an  inappropriate  name.  There 
are  two  slightly  different  methods  of  applying  the  asphalt,  both  of 
which  have  been  patented.  They  will  be  referred  to  as  Warren's 
and  Whinery's,  after  the  inventors. 

696.  WARREN'S  METHOD.*  Upon  the  subsoil  is  placed  a  4-inch 
layer  of  broken  stone  which  is  thoroughly  rolled.  On  this  stone 
foundation  is  spread  a  coat  of  thin  asphaltic  cement,  which  enters 
the  interstices  of  the  stone  holding  its  fragments  together  and 
forming  a  surface  with  which  the  wearing  coat  will  readily  and 
firmly  unite.  The  asphalt  macadam  consists  of  a  mixture  of  -as- 
phaltic cement  and  broken  stone,  the  fragments  of  the  latter  vary- 
ing from  1  to  2  inches  in  the  largest  dimensions  to  fine  dust.  The 
ingredients  of  the  asphaltic  macadam  are  mixed  about  as  described 
for  the  wearing  coat  of  the  ordinary  asphalt  pavement  (§  627). 
The  mixture  of  asphaltic  cement  and  stone  is  spread,  while  still 
hot,  of  such  a  thickness  as  to  be  2  inches  after  being  thoroughly 
rolled  with  a  road  roller  (§  336)  weighing  15  to  20  tons.  On  top  of 
the  asphalt  macadam  is  spread  a  layer  of  asphaltic  cement,  partly 
to  seal  the  surface  against  the  entrance  of  air  and  water,  and  partly 
to  bind  together  the  fragments  forming  the  wearing  surface.  While 
the  surface  of  the  asphaltic  cement  is  still  sticky  there  is  spread 
over  it  a  thick  coat  of  fine  stone  chips,  which  are  then  rolled  and 
the  road  is  ready  for  traffic. 

The  finished  roadway  presents  a  rough  gritty  surface,  which 
has  more  of  the  characteristics  of  an  ordinary  broken-stone  road 

*  Jour.  Assoc,  oi  Engineering  Societies,  Vol.  28,  p.  297-302 ;  Engineering  Neves, 
Vol.  47,  p.  79-80 ;  Engineering  Record,  Vol.  45,  p.  84-85. 


ART.   5.]  ASPHALT   MACADAM.  453 

than  of  the  usual  asphalt  pavement.  Less  asphaltic  cement  is 
required  for  a  given  thickness  of  asphalt  concrete  than  for  the 
asphalt  mortar  of  the  wearing  coat  of  the  ordinary  asphalt 
pavement,  since  the  larger  the  fragments  of  the  aggregate  the 
less  the  per  cent  of  voids,  and  consequently  the  less  cement 
required.  It  is  claimed  that  no  single  stone  has  been  dislodged  in 
any  of  the  seven  cities  in  which  experimental  sections  have  been 
built.  It  is  also  claimed  that  asphalt  macadam  is  superior  to 
ordinary  asphalt  pavement,  since  the  angular  fragments  of  the 
broken  stone  used  in  the  former  are  less  mobile  than  the  rounded 
sand  grains  used  in  the  latter,  and  hence  the  cement  in  the  former 
may  be  made  softer  and  may  also  be  worked  at  a  lower  tempera- 
ture than  in  the  latter.  The  softer  the  asphaltic  cement,  the  more 
durable  it  is;  and  the  lower  the  temperature  at  which  it  is  worked, 
the  less  the  danger  of  damage  by  overheating  it. 

697.  WHINERY'S  METHOD.*  The  foundation  may  be  either 
broken  stone  or  hydraulic  cement  concrete,  depending  upon  the 
relative  cost  of  the  two  and  also  upon  the  supporting  power  of  the 
subsoil.  The  wearing  coat  consists  of  a  layer  of  crushed  stone  the 
voids  of  which  are  filled  with  a  mixture  similar  to  that  used  for  the 
wearing  coat  of  sheet  asphalt  pavements.  Broken  stone  of  properly 
graded  sizes  is  spread  on  the  foundation  to  the  requisite  thickness, 
which,  either  before  or  after  it  is  thus  spread,  is  heated  to  a  tem- 
perature of  about  300°  F.  A  hot  mixture  of  asphaltic  cement  and 
mineral  grains  is  spread  over  the  top  of  the  layer  of  hot  crushed 
stone  in  a  sufficient  quantity  to  fill  the  voids  in  the  stone  and  to  level 
up  the  unevenness  of  the  surface,  the  layer  being  properly  graded 
with  paving  rakes.  When  this  operation  is  completed  a  steam 
roller  of  the  asphalt  type  weighing  not  less  than  ten  tons  is  to  be 
operated  over  the  surface  until  (1)  the  plastic  composition  is  forced 
into  the  voids  in  the  crushed  stone,  (2)  the  unevenness  of  the  surface 
is  filled  up,  and  (3)  the  whole  mass  is  thoroughly  compressed  and 
solidified.  The  roadway  is  then  complete,  and  after  giving  it  time 
to  become  cold  and  hard  the  street  is  opened  to  travel. 

No  pavement  of  this  kind  has  been  constructed,  but  the  in- 
ventor, an  engineer  of  large  experience  in  laying  asphalt  pavements, 

*  Engineering  News,  Vol.  45,  p.  413-14. 


454  ASPHALT   PAVEMENTS.  [CHAP.  XIII. 

claims  that  it  will  have  the  following  advantages  over  ordinary 
sheet  asphalt  pavements.  1.  The  first  cost  will  be  materially  less. 
2.  It  will  offer  a  better  foothold  to  horses.  3.  It  will  be  at  least  as 
durable  as  the  ordinary  sheet  pavement.  4.  It  will  not  shift  under 
travel  and  work  into  waves.  5.  It  will  not  crack.  6.  It  can  be 
repaired  more  cheaply  and  with  less  skilled  labor  than  can  the 
ordinary  sheet  pavement.  On  the  other  hand  the  asphalt  macadam 
will  not  be  so  smooth  and  probably  not  so  noiseless  as  the  ordinary 
asphalt  pavement. 

Art.  6.     Coal-tar  Roads  and  Pavements. 

698.  Asphalt  is  a  natural  bitumen,  while  coal  tar  is  an  artificial 
bitumen.  The  latter  is  produced  by  the  distillation  of  coal,  and 
is  usually  a  bi-product  in  the  manufacture  of  illuminating  gas. 
Tar  is  a  very  complex  hydro-carbon,  and  its  character  varies  con- 
siderably with  the  system  of  manufacture.  It  naturally  contains 
volatile  oils  and  water;  and  when  re-distilled  produces  what  is 
known  to  the  trade  as  paving  pitch  or  paving  cement,  which  is 
designated  as  distillate  No.  1,  2,  3,  4,  5,  or  6,  according  to  its  hard- 
ness. Distillate  No.  4,  which  is  much  used  as  a  substitute  for 
asphalt,  has  a  specific  gravity  of  about  1.30,  and  contains  about 
65  to  70  per  cent  of  bitumen  soluble  in  carbon  bisulphide.  It 
will  almost  stick  to  the  fingers  when  worked  in  the  hands  at  a  tem- 
perature of  70°  F.  It  is  very  susceptible  to  changes  of  tempera- 
ture, becomes  semi-fluid  under  the  heat  of  summer,  and  hard  and 
brittle  at  ordinary  winter  temperatures.  It  must  be  shipped  in 
tight  barrels.  No.  6  is  much  used  for  filling  the  joints  of  brick 
pavements,  is  considerably  harder  than  No.  4,  and  may  be  shipped 
in  slack  barrels.  The  price  of  tar  varies  from  6  to  10  cents  a  gallon 
according  to  the  locality  and  the  demand. 

Coal  tar  was  formerly  employed  to  a  considerable  extent  for 
paving  purposes,  the  resulting  pavement  being  much  the  same  as 
sheet  asphalt;  but  this  use  of  coal  tar  has  now  practically  been 
abandoned.  Tar  is  still  used  to  a  limited  extent,  chiefly  in  Can- 
ada and  England,  as  a  binding  material  for  macadam  for  carriage 
ways;  and  is  also  used  a  little  in  the  construction  of  foot  ways. 

699.  COAL-TAR  PAVEMENTS.  Numerous  attempts  have  been 
made  to  construct  a  pavement  by  the  use  of  coal  tar  as  a  cementing 


ART.   6.]  COAL-TAR   ROADS   AND   PAVEMENTS.  455 

material  in  place  of  asphalt  or  in  conjunction  with  it.  This  form  of 
pavement  was  laid  somewhat  extensively  in  Washington,  D.  C, 
from  1872  to  1887.  The  earlier  pavements  were  laid  under  many 
different  patents,  of  many  different  mixtures,  receiving  their  name 
generally  from  that  of  the  patentee.  Most  of  them  were  signal 
failures,  although  some  were  fairly  durable.  In  1886  Congress  in 
making  an  appropriation  for  pavements  in  Washington  stipulated 
that  no  contract  for  an  asphalt  pavement  should  be  made  at  a 
higher  price  than  $2.00  a  square  yard;  and  no  bids  having  been 
received  for  asphalt  pavements  for  less  than  $2.25,  a  considerable 
quantity  of  coal-tar  pavements  were  laid  during  the  years  1886 
and  1887. 

700.  Specifications.  The  specifications  employed  at  Wash- 
ington, D.  C,  in  1886-87  for  coal-tar  distillate  pavements  are  as 
follows :  * 

701.  "Road-bed.  The  space  over  which  the  pavement  is  to  be  laid  shall 
be  excavated  to  the  depth  of  six  inches  below  the  top  of  the  surface  of 
the  pavement  when  completed.  Any  objectionable  or  unsuitable  material 
below  the  bed  shall  be  removed  and  the  space  be  filled  with  clean  gravel  or 
sand  well  rammed.  The  bed  shall  then  be  trimmed  so  as  to  be  exactly  par- 
allel to  the  surface  of  the  new  pavement  when  completed,  and  the  entire 
road-bed  shall  be  thoroughly  rolled  with  a  heavy  steam-roller. 

702.  "Base.  The  base  shall  be  composed  of  clean  broken  stone  which 
will  pass  through  a  three-inch  ring  and  which  shall  be  thoroughly  coated 
with  No.  4^  coal-tar  paving  cement  in  the  proportion  of  about  one  gallon  to 
the  square  yard  of  the  base.  This  layer  shall  be  well  rammed  and  shall 
then  be  rolled  with  a  steam-roller.     The  depth  after  rolling  shall  be  4  inches. 

703.  "Binder.  The  second  or  binder  course  shall  be  composed  of  clean 
broken  stone,  thoroughly  screened,  not  exceeding  \\  inches  in  the  largest 
dimension,  and  No.  4  coal-tar  paving  cement.  The  stone  shall  be  heated  to 
a  temperature  between  230°  and  250°  F.  by  passing  it  through  revolving 
heaters,  and  shall  be  thoroughly  mixed  by  machinery  with  the  paving  cement 
in  about  the  proportion  of  one  gallon  of  tar  to  one  cubic  foot  of  stone.  The 
mixture  shall  be  hauled  upon  the  work,  be  spread  upon  the  base  course  at 
least  2  inches  thick,  and  be  immediately  rammed  and  rolled  with  hand  and 
steam-rollers.  The  base  and  the  binder  shall  together  measure  at  least  4£ 
inches  when  compacted. 

704.  "  Wearing  Surface.  The  wearing  surface  shall  be  composed  of  the 
following  materials,  in  the  following  proportions: 

*  Eeport  of  tho  Operations  of  the  Engineering  Department  of  the  District  of 
Columbia  for  the  year  ending  June  30,  1890,  p.  165-66. 


45G  ASPHALT   PAVEMENTS.  [CHAP.   XIII. 

Clean  sharp  sand 63  to  58  per  cent 

Powdered  limestone 28  "  23    "       u 

Paving  cement 13  "  15    "      « 

Hydraulic  cement 0.90    "       " 

Slaked  lime 0.15    '«       " 

Flower  of  sulphur 0.10    "      " 

"  The  sand  shall  be  clean  sharp  river  sand,  free  from  clay,  and  of  such  a 
size  that  not  more  than  twenty  per  cent  shall  be  retained  upon  a  sieve  of 
twenty  meshes  to  the  inch,  and  not  more  +han  five  per  cent  shall  pass  a 
sieve  of  seventy  meshes  to  the  inch,  about  sixty  per  cent  to  be  coarser  than 
forty  meshes  to  the  inch.  The  powdered  stone  or  stone  dust  shall  be  the 
residue  from  crushing  the  stone  for  the  base  and  the  binder;  and  shall  be  of 
such  a  degree  of  fineness  that  16  per  cent  by  weight  shall  be  an  impalpable 
powder,  and  that  the  whole  of  it  shall  pass  a  No.  26  screen.  The  paving 
cement  shall  be  composed  of  refined  Trinidad  asphalt,  25  to  30  parts,  and 
No.  4  coal-tar  paving  cement,  75  to  70  parts.  The  refined  asphalt  shall  con- 
tain at  least  sixty  per  cent  of  bituminous  matter  soluble  in  carbon  bisul- 
phide. The  No.  4  coal-tar  paving  cement  shall  correspond  to  a  standard 
to  be  furnished  by  the  Engineer  Commissioner,  and  shall  be  free  from  ex- 
cess of  sooty  matter,  napthaline,  and  creosote  oils.  The  hydraulic  cement, 
lime,  and  sulphur  shall  be  of  the  best  commercial  quantity.  The  materials 
for  the  wearing  surface  shall  be  heated  to  not  over  260°  F., — the  paving 
cement  in  kettles,  the  sand  and  stone  dust  in  revolving  heaters.  The  hy- 
draulic cement,  lime,  and  sulphur  shall  be  added  cold  to  the  sand  and  stone 
dust  in  the  sand  box  before  going  to  the  mixer.  The  ingredients  shall  be 
thoroughly  mixed  by  approved  machinery. 

705.  "Laying.  The  wearing  coat  shall  be  hauled  upon  the  street,  and  be 
spread  upon  the  binder  course  in  a  layer  2  inches  thick  with  hot  iron  rakes 
and  other  suitable  appliances.  It  shall  be  immediately  compacted,  while 
hot  and  plastic,  with  hot  tamping  irons  and  hand  rollers.  It  must  be 
thoroughly  rolled  and  cross  rolled  until  it  has  become  hard  and  solid.  In 
spreading  the  material  the  joints  between  the  different  loads  shall  be  diagonal 
to  the  line  of  the  street.  The  surface  shall  be  finished  with  a  dusting  of  dry 
hydraulic  cement  rolled  in.  In  cool  weather,  or  when  ordered,  the  carts 
carrying  the  mixture  shall  be  protected  with  canvas  covers.  The  wearing 
coat  shall  be  at  least  1£  inches  thick  after  rolling." 

706.  COST.  Construction.  The  first  cost  of  coal-tar  pave- 
ments has  been  only  a  trifle  under  the  prevailing  prices  for  sheet- 
asphalt  pavements.  In  Washington  D.  C,  from  1873  to  1878, 
745,305  square  yards  of  coal-tar  pavements  of  various  kinds  were 
laid  at  prices  ranging  from  $1.74  to  $3.70  per  square  yard.  These 
pavements  proved  very  unreliable,  either  through  inherent  defects 
in  the  materials  used  or  owing  to  faulty  methods  of  construction; 


ART.  6.]  COAL-TAR   ROADS   AKD   PAVEMENTS.  457 

and  consequently  for  some  years  thereafter  no  coal-tar  pavements 
were  laid.  A  return  to  coal-tar  pavements  in  1887-89  was  forced 
upon  the  city  by  the  act  of  Congress  which  specified  that  no  con- 
tract should  be  made  for  asphalt  pavements  for  a  greater  price 
than  $2.00  per  square  yard.  The  lowest  bid  received  for  such 
pavements  was  $2.25  per  square  yard,  and  consequently  a  con- 
siderable quantity  of  tar  pavements  was  laid,  the  prices  of  it  being 
from  $1.98  to  $2.00  per  square  yard.  These  pavements  were  laid 
under  the  specifications  in  §  700-05. 

707.  Maintenance.  Up  to  June  30,  1887,  the  average  cost  of 
maintaining  all  the  coal-tar  distillate  pavements  laid  from  1871  to 
1878  was  7.2  cents  per  square  yard  per  annum;  but  the  work  of 
one  contractor  was  so  poor  that  it  was  necessary  to  re-surface  the 
pavements  laid  by  him  when  they  were  only  two  years  old,  and 
excluding  the  work  of  this  contractor  the  cost  of  maintenance  was 
5,5  cents  per  square  yard  per  annum.*  "  For  the  first  five  years, 
the  annual  average  was  3.7  cents  per  square  yard;  for  the  second 
five  years,  6  cents;  and  for  the  last  five  years,  6.6  cents.  That  a 
durable  coal-tar  pavement  can  be  laid  is  proved  by  the  fact  that 
the  average  cost  of  maintenance  of  158,595  square  yards  of  Vul- 
canite pavement  (for  specifications  of  the  same  see  §  700-05)  was 
only  2.9  cents  per  square  yard  per  annum  for  fourteen  years,  for 
the  first  five  years  the  average  being  0.3  cents  per  square  yard,  for 
the  second  five  years  4.2  cents  per  square  yard,  and  for  the  last 
four  years  4  cents  per  square  yard."  f 

Up  to  June  30,  1901,  the  average  cost  of  maintenance  of  the 
tar  pavements  laid  in  Washington  in  1887-89  had  been  3.5  cents 
per  square  yard  per  annum.  This  result  was  obtained  as  follows: 
The  Report  of  the  Operations  of  the  Engineering  Department  of 
the  District  of  Columbia  for  the  year  ending  June  30,  1901,  pages 
8  to  51,  gives  the  location,  the  kind,  and  the  details  of  the  cost  of 
all  the  pavements  in  Washington,  including  the  average  annual 
cost  per  square  yard  for  the  pavement  laid  under  each  contract.! 
During  1887-89,  132,063  square  yards  of  pavement  were  laid  under 

♦Report  of  Engineer  Commissioner,  June  30,  1887,  p.  60-62. 
\Ibid.,  p.  62. 

{For  the  cost  for  each  individual  year,  see  the  Reports  for  1898,  p.  ix-rvii;  1899, 
p.  4-11;  1900,  folding  sheets  between  pages  82  and  83. 


458  ASPHALT   PAVEMENTS.  [CHAP.   XIII. 

thirty-six  contracts,  and  the  average  of  the  annual  cost  under  the 
several  contracts  is  3.5  cents  per  square  yard,  as  stated  above.  This 
method  of  deducing  the  average  takes  no  account  of  the  areas  of 
the  different  pieces,  and  consequently  is  not  mathematically  cor- 
rect; but  the  error  is  immaterial.  The  areas  range  mostly  from 
2,000  to  4,000  square  yards,  one,  however,  being  18,000.  The 
average  age  of  the  pavements  was  12.6  years.  Of  the  thirty-six 
pieces  of  tar  pavement  as  above,  fourteen  had  been  re-surfaced 
before  July  1,  1901,  the  average  age  at  the  time  of  re-surfacing 
being  11.7  years. 

708.  The  above  data  on  the  cost  of  maintenance  of  coal-tar 
distillate  pavements  suggest  a  comparison  with  the  correspond- 
ing data  for  asphalt  pavements.  According  to  Table  47,  page 
442,  there  were  laid  in  Washington  during  the  years  1886,  1887, 
1889,  and  1890,  114,408  square  yards  of  asphalt  pavement,  for 
which  the  cost  of  maintenance  was  1.13  cents  per  square  yard  per 
annum.  The  corresponding  cost  of  tar  pavements  laid  from  1886 
to  1889  was  3.5  cents,  and  therefore  we  may  conclude  that  the 
cost  of  maintenance  of  tar  pavements  is  practically  three  times 
as  much  as  that  of  asphalt  pavements.  Any  attempt  thus  to  com- 
pare the  cost  of  maintenance  of  tar  and  asphalt  pavements  is  open 
to  the  criticism  that  the  mathematical  process  of  deducing  the 
average  is  not  strictly  correct,  and  also  that  the  amount  of  traffic 
may  not  be  the  same  in  the  two  cases,  and  further  that  part  of  the 
repairs  in  each  case  was  due  to  openings  made  in  the  streets  inde- 
pendent of  the  condition  of  the  pavements;  but  nevertheless  the 
general  conclusion  is  at  least  approximately  true.  The  use  of  tar 
pavements  has  practically  been  abandoned,  chiefly  on  account  of 
the  excessive  cost  of  maintenance. 

709.  TAR  MACADAM.  Broken  stone  with  a  tar  binder  has  been 
used  for  road  purposes  in  a  comparatively  small  way  in  England 
for  twenty  or  thirty  years  past;  and  the  experience  of  Hamilton, 
Ontario,  Canada,  with  this  form  of  pavement  has  lately  attracted 
considerable  attention  in  this  country.  In  a  general  way,  two 
methods  have  been  employed  in  using  tar  as  a  binder  for  broken 
stone,  viz.:  (1)  the  broken  stone  is  mixed  with  sufficient  tar  more 
or  less  nearly  to  fill  the  voids,  and  then  the  mixture  is  deposited 
and  compacted,  the  process  being  very  much  the  same  as  that  em- 


ART.   6.]  COAL-TAR   ROADS   AND   PAVEMENTS.  459 

ployed  in  laying  hydraulic  cement  concrete;  or  (2)  the  broken 
stone  is  laid  and  rolled,  and  then  a  layer  of  tar  is  added  and  rolled, 
the  intention  being  to  force  the  tar  into  the  interstices  of  the  broken 
stone  much  as  the  stone-dust  binder  is  worked  into  a  broken-stone 
road.  The  product  in  the  first  case  could  appropriately  be  called 
tar  concrete,  and  in  the  second  tar  macadam;  and  they  will  be  so 
designated  in  this  discussion.  The  former  seems  to  be  the  more 
common  in  England,  and  the  latter  in  Canada.  Notice  that  these 
two  methods  are  substantially  the  same  as  Warren's  and  Whinery's 
method  for  making  asphalt  macadam — see  §  696  and  §  697,  re- 
spectively. 

710.  The  Tar.  The  tar  should  contain  not  more  than  5  per 
cent  of  water,  and  not  less  than  55  per  cent  of  pitch.  The  ordinary 
gas  tar  should  be  boiled  until  it  is  capable,  when  cool,  of  being  drawn 
out  into  thread-like  filaments;  and  the  best  results  are  not  likely 
to  be  obtained  by  attempting  to  secure  the  proper  consistency  by 
adding  thicker  tar,  since  it  is  difficult  to  get  a  uniform  mixture. 
Any  clean  broken  stone  or  gravel  may  be  used. 

711.  The  Construction.  The  subgrade  is  prepared  as  for  a 
pavement  or  for  the  ordinary  broken-stone  road,  and  the  founda- 
tion consists  of  a  layer  of  broken  stone,  usually  4  inches  thick, 
which  is  thoroughly  rolled. 

In  making  tar  concrete,  care  must  be  taken  thoroughly  to  mix 
the  tar  and  the  stone,  the  former  being  hot  and  the  latter  dry. 
The  mixing  is  done  with  shovels  on  a  board  platform,  the  tar 
being  poured  over  the  stone.  Each  fragment  of  stone  should  be 
thoroughly  covered  with  tar;  but  more  tar  than  enough  to  fill  the 
voids  is  objectionable,  since  it  increases  the  cost  and  decreases  the 
durability  of  the  road.  Usually  10  or  12  gallons  are  required  for 
a  cubic  yard  of  unscreened  stone.  The  mixture  is  then  placed  in 
the  road,  and  rolled  while  hot  with  the  usual  road  roller,  sand  or 
dust  being  sprinkled  over  the  surface  to  prevent  the  tar  from 
sticking  to  the  roller.  Only  a  comparatively  small  amount  of  rolling 
is  required  to  consolidate  the  mass.  Not  infrequently  a  wearing 
coat,  consisting  of  a  half  inch  to  1  inch  of  tar  and  screenings,  is 
added  on  the  top  of  the  tar  concrete ;  and  herein  the  two  methods 
referred  to  above  merge  one  into  the  other. 

In  laying  tar  macadam,  the  broken  stone  is  rolled  until  the 


460  ASPHALT    PAVEMENTS.  [CHAP.    XIII. 

fragments  do  not  move  under  the  foot  in  walking  over  the  surface, 
and  then  a  layer  of  hot  tar  is  poured  upon  the  surface  and  is  evenly 
spread  over  it  with  brooms  or  shovels,  after  which  it  is  rolled.  If 
honeycombed  spots  appear  while  the  rolling  is  in  progress,  more 
tar  is  added.  After  the  surface  of  the  layer  of  broken  stone  has 
been  thoroughly  filled  with  tar,  the  surface  is  flushed  with  moder- 
ately soft  tar,  and  over  this  is  strewn  a  thin  layer  of  stone  chips 
about  J  to  \  inch  in  longest  dimension;  and  then  the  surface  is  again 
rolled,  after  which  the  road  is  thrown  open  to  traffic. 

712.  Cost.  In  Hamilton,  Ontario,  the  cost  of  tar-macadam 
roads  is  as  follows :  broken  limestone  95  cents  per  cubic  yard  deliv- 
ered; coal  tar  $2.60  per  barrel  on  the  road;  labor  18  cents  per  hour; 
and  the  total  cost  of  the  tar-macadam  roadway  85  cents  per  square 
yard. 

713.  Merits  and  Defects.  Obviously  tar  concrete  and  tar 
macadam  are  suitable  only  for  comparatively  light-traffic  roads, 
and  are  more  appropriately  compared  with  ordinary  broken-stone 
roads  than  with  asphalt  pavements.  The  use  of  a  tar  binder  ren- 
ders the  roadway  impervious  to  water,  makes  it  frost  proof,  lessens 
the  tendency  of  the  road  materials  to  grind  to  powder,  and  con- 
sequently decreases  the  tendency  to  produce  dust  and  mud.  It 
is  easily  cleaned,  since  there  is  less  likelihood  of  loosening  the  sur- 
face stones;  and  it  is  easily  repaired  where  opened  for  water  or 
gas  connections. 

It  is  hardly  probable  that  tar  macadam  will  come  into  anything 
like  general  use,  either  for  country  roads  or  for  city  streets.  The  cost 
of  tar  macadam  is  nearly  or  quite  as  much  as  that  of  the  ordinary 
broken-stone  road  (compare  §  712  with  §  359-62);  and  the  con- 
struction of  the  former  is  neither  so  simple  nor  so  certain  as  the 
latter.  Tar  macadam  is  of  doubtful  durability,  since  coal  tar  is 
subject  to  oxidation  by  the  atmosphere,  which  renders  it  brittle 
and  devoid  of  cementing  power.  Tar  is  affected  by  changes  of 
temperature,  and  becomes  friable  in  cold  weather  and  soft  in  warm. 
There  is  less  chance  of  success  with  tar  macadam  in  the  future  than 
in  the  past,  since  in  the  present  stage  of  manufacture,  water  gas 
is  being  substituted  largely  for  coal  gas,  the  quantity  of  gas  tar 
produced  is  diminishing,  its  price  is  increasing,  and  its  quality  is 
deteriorating. 


ART.   6.]  COAL-TAR   ROADS   AND   PAVEMENTS.  461 

It  is  probable  that  the  most  favorable  field  for  tar  macadam 
is  as  a  substitute  for  ordinary  crushed  stone  on  grades  so  steep  as 
to  wash  seriously,  and  as  a  substitute  for  cobble  gutters  on  crushed- 
stone  streets. 


CHAPTER  XIV. 
BRICK  PAVEMENTS. 

715.  A  brick  pavement  consists  of  brick  set  on  edge  on  a  suit- 
able foundation — either  concrete,  gravel,  a  course  of  brick  flat- 
wise, or  a  layer  of  plank.  Such  pavements  have  been  used  in 
Holland  for  perhaps  a  century,  and  to  a  much  less  extent  and  for 
a  shorter  period  in  northern  England.  Brick  pavements  were 
first  used  in  the  United  States  in  1870  at  Charleston,  W.  Va.,  a 
place  having  a  population  of  12,000.  The  experiment  was  tried 
with  a  short  section — less  than  a  block; — and  in  1873  a  block  on 
the  principal  business  street  was  laid  with  a  good  quality  of  build- 
ing brick,  and  is  still  in  service  after  29  years.  A  block  of  brick 
pavement,  laid  in  1875  on  a  leading  business  street  of  Blooming- 
ton,  Illinois,  a  place  of  20,484  population  in  1890,  though  con- 
structed of  an  inferior  building  brick  made  of  a  superior  clay, 
continued  in  service  for  20  years. 

At  present  brick  is  the  only  paving  material  employed  in  most 
of  the  smaller  cities  of  the  Mississippi  Valley,  and  it  is  used  exten- 
sively in  many  of  the  larger  cities  in  that  territory.  In  all  parts 
of  this  country,  the  use  of  brick  for  residence  streets  and  light 
traffic  business  streets  is  rapidly  increasing.  A  recent  canvass 
shows  about  as  much  brick  pavement  in  progress  as  granite  block, 
asphalt,  and  wood  combined.  There  are  in  this  country  nearly 
two  hundred  plants  devoted  to  the  manufacture  of  paving  brick, 
some  having  annual  outputs  of  60,000,000  to  100,000,000  bricks. 

Art.  1.     The  Brick. 

716.  A  paving  brick  is  simply  a  brick  which,  owing  to  careful 
selection  of  the  clay  and  to  skilful  manufacture,  is  so  hard  and 
tough  that  it  will  resist  the  crushing  and  the  abrading  action  of 
the  traffic. 

462 


ART.  1.]  THE   BRICK.  463 

717.  THE  CLAY.  Three  distinct  classes  of  clay  are  employed 
in  the  manufacture  of  paving  brick:  surface  clays,  impure  fire 
clays,  and  shales.  Surface  clays  are  almost  exclusively  used  for 
the  manufacture  of  building  bricks;  but  are  not  ordinarily  suitable 
for  making  paving  bricks,  since  it  is  practically  impossible  to  burn 
them  hard  enough  without  their  losing  their  shape.  On  account, 
of  its  infusibility,  pure  fire  clay  is  unsuitable  for  making  paving 
brick,  the  brick  being  expensive  to  burn  and  lacking  density,  hard- 
ness, and  strength;  but  quite  impure  fire  clay  makes  a  fair  quality 
of  paving  brick,  although  the  process  of  manufacture  is  compara- 
tively expensive.  Bricks  made  from  impure  fire  clay  are  usually 
light  in  color,  varying  from  cream  to  buff,  and  ordinarily  are  quite 
porous,  absorbing  from  2.5  to  7.0  per  cent  of  water.  Most  paving 
bricks  are  made  from  shale, — an  impure,  hard,  laminated  clay 
which  has  been  subjected  to  great  pressure  by  the  superincumbent 
earth  strata.  Shale  is  widely  distributed  and  makes  a  much 
better  and  cheaper  paving  brick  than  either  surface  or  fire  clay. 

The  different  classes  of  clay  so  shade  by  imperceptible  degrees 
one  into  the  other  that  it  is  impossible  sharply  to  discriminate 
them.  Surface  clays  are  soft  and  unconsolidated,  and  are  found 
at  or  near  the  natural  surface.  Shales  are  dense  and  rock-like, 
but  are  easily  reduced  to  powder  and  are  readily  worked  into  a 
plastic  mass  when  mixed  with  water.  Shale  is  often  incorrectly 
called  soapstone,  from  which  it  differs  in  nearly  every  respect. 
Shale  is  also  frequently,  but  erroneously,  called  slate,  from  which 
it  differs  only  slightly  in  origin  and  composition;  but  slate,  unlike 
shale,  can  not  be  rendered  plastic  by  mixing  it  with  water.  The 
only  method  of  distinguishing  between  shale  and  impure  fire  clay, 
except  by  a  kiln  test,  is  the  fact  that  shale  gives  a  conchoidal  frac- 
ture while  fire  clay  does  not. 

718.  Chemical  Composition.  It  is  not  wise  to  enter  into  any 
extended  consideration  of  the  chemical  composition  of  brick  clays, 
since  the  subject  is  very  complicated,  and  since  the  engineer  is 
interested  only  in  the  physical  properties  of  the  finished  product 
and  should  not  attempt  to  prescribe  the  materials  or  to  limit  the 
methods  employed  by  the  manufacturer.  However,  a  brief  dis- 
cussion of  the  subject  may  be  of  value  as  showing  some  of  the  limi- 


464  BRICK  PAVEMENTS.  [CHAP.  XIY. 

tations  upon  the  manufacture.  Clay  varies  widely  in  its  chem- 
ical composition,  the  essential  ingredient  being  kaolin,  a  hydrous 
silicate  of  alumina  having  the  composition: 

Silica , 46 .3  per  cent 

Alumina 39 . 8 

Water 13.9    "      " 

Total  100.0    "      " 

Kaolin  may  be  considered  pure  clay,  but  is  rarely  if  ever  found  pure 
in  nature.  It  is  commonly  mixed  with  varying  quantities  of  silica, 
lime,  magnesia,  ferric  oxide,  potash,  and  soda.  The  presence  of 
these  substances,  which  may  be  regarded  as  the  impurities  of  clay, 
and  the  physical  condition  under  which  they  exist,  cause  the  wide 
variation  in  the  clays  themselves  and  to  a  great  extent  in  the 
product  made  from  them. 

The  chemical  composition  of  shale  suitable  for  making  paving 
brick  usually  ranges  between  the  limits  given  in  Table  49.* 

TABLE  49. 
Chemical  Composition  of  Paving-brick  Shales. 

Constituents.  Min.         Max.  Aver. 

Silica (Si02) 49.0  %  75.0%  56.0% 

Alumina  (A1203) n-0  "    25.0  "     22.5  " 

Ignition  loss  (mainly  H20) 3.0  "    13.0  "       7.0  " 

Moisture  (H,0)..... 0.5  "     3.0  "       1 


5  " 


Total  non-fluxing  constituents 87 .0  " 

Sesquioxide  of  iron  (FeA) 2.0"  9.0"  6.7" 

Lime  (CaO) 0.2"  3.5"  1.2  " 

Magnesia  (MgO) 0.1"  3.0"  1.4" 

Alkalies  (K20,  Na,0) 1.0  "  5.5  "  3.7 * 

Total  fluxing  constituents * 13 . 0  * 

Grand  total 100.0  4 

Silica  is  practically  infusible,  and  its  presence  prevents,  or  al 
least  reduces,  the  tendency  of  the  clay  to  crack,  distort  and  shrink ; 
but  the  more  silica  the  greater  plasticity  and  adhesiveness  of  the 

♦Vitrified  Paving  Brick,  by  H.  A.  Wheeler,  p.  18.    84  p.  8J"XS".     T.  A.  Eandall 
&  Co.,  Indianapolis,  Ind.,  1895. 


ART.   1.]  THE   BRICK.  465 

clay,  and  the  less  the  strength  and  the  toughness  of  the  brick. 
Alumina  will  resist  the  highest  temperature,  and  gives  plasticity 
and  adhesiveness  to  the  clay  and  strength  to  the  brick;  but  it 
causes  the  clay  to  shrink,  warp,  and  crack  in  drying.  Iron  in  con- 
siderable quantities  has  a  fluxing  effect  with  silica,  cementing  it  to- 
gether and  giving  it  strength.  Iron  is  not  the  most  valuable  of 
constituents  in  this  regard,  and  its  presence  is  not  essential  to  a 
first-class  paving  brick.  The  red  color  of  brick  is  due  to  the 
presence  of  iron,  but  more  to  its  form  than  to  its  amount.  Many 
erroneously  believe  that  only  red  brick  have  sufficient  strength  and 
durability  for  paving  purposes.  Lime  and  magnesia  are  infusible 
by  themselves  or  with  alumina,  but  fuse  in  the  presence  of  an 
excess  of  silica  and  give  strength  to  the  brick.  If  the  lime  is  in 
the  form  of  feldspar  or  a  silicate,  the  more  the  better.  But  if  it  is 
present  in  the  form  of  carbonate,  it  weakens  the  brick;  and  if 
present  as  concretions  or  pebbles,  and  not  finely  ground,  the  quick- 
lime resulting  from  the  burning  is  likely  to  cause  swelling  or  crack- 
ing when  the  brick  is  wet.  Potash  (K20)  and  soda  (Na20)  fuse  at 
lower  temperatures  than  the  other  constituents  of  clay,  and  their 
presence  in  suitable  quantities  is  very  desirable. 

719.  Physical  Properties.  A  chemical  analysis  of  a  clay  may 
furnish  sufficient  evidence  upon  which  to  condemn  it  for  brick- 
making  purposes,  but  never  enough  for  its  indorsement.  The 
following  physical  properties  are  important  factors  in  determining 
the  value  of  a  brick  clay:  1,  its  plasticity;  2,  the  amount  of  water 
required  to  make  a  plastic  mass;  3,  the  amount  of  shrinkage,  both 
in  burning  and  in  drying;  4,  the  rapidity  of  drying  and  also  of 
burning;  5,  the  temperature  of  incipient  and  complete  vitrifica- 
tion; 6,  the  density  before  and  after  burning;  and  7,  the  strength 
of  the  burned  brick. 

720.  Manufacture  of  the  Brick.    Soft,  homogeneous  clay 

may  be  run  through  rollers,  to  crush  the  lumps,  and  from  the  crusher 
it  may  go  directly  to  the  brick  machine ;  but  it  is  usually  desirable 
to  run  it  first  through  a  pug  mill,  where  it  is  mixed  and  worked 
with  water  into  a  plastic  mass.  Hard  clays  and  shales  are  usually 
reduced  to  a  powder  in  a  dry  pan,  which  consists  of  two  heavy 
rollers  or  wheels  running  in  a  revolving  pan  having  a  perforated 
bottom.    It  is  important  to  have  the  clay  finely  pulverized,  be- 


466  BRICK   PAVEMENTS.  [CHAP.   XIY. 

cause  it  will  then  fuse  at  a  lower  temperature,  and  also  because  fine- 
ness is  necessary  to  the  production  of  an  even  and  close-grained 
texture  which  conduces  to  make  the  brick  tough  and  impervious. 
The  powdered  clay  is  screened  and  then  tempered  with  water  in  the 
pug  mill  or  a  wet  pan.  Fire  clays  are  sometimes  both  crushed  and 
tempered  in  a  wet  pan,  which  is  similar  to  a  dry  pan  except  that 
the  bottom  is  water  tight.  The  wet  pan  gives  better  results  than 
the  pug  mill,  as  the  clay  can  be  retained  in  the  pan  until  it  is  thor- 
oughly tempered;  but  as  it  requires  a  large  plant,  and  takes  more 
labor  and  power,  it  is  not  usually  used  for  paving  brick.  The  more 
thoroughly  the  clay  is  worked  or  tempered,  the  more  uniform  and 
better  will  be  the  brick. 

721.  Molding.  Paving  brick  are  usually  made  by  the  stiff- 
mud  process,  although  a  few  yards  still  use  the  old-fashioned  soft- 
mud  and  re-pressing  system.  The  molding  is  usually  done  by  an 
auger  machine  which  forces  the  tempered  clay  or  stiff  mud  through 
a  die,  thus  giving  a  continuous  bar  of  compressed  clay  which 
passes  under  an  automatic  machine  that  cuts  the  bar  into  brick 
of  the  desired  size.  Instead  of  an  auger  producing  a  continuous 
stream  of  clay,  reciprocating  plungers  are  sometimes  employed, 
which  give  an  intermittent  bar.  The  auger  machine  is  the  cheap- 
est, and  is  almost  universally  used.  Formerly  the  dies  were  made 
about  4 J  X  2J  inches  in  size,  producing  an  end-cut  brick;  but  of 
late  dies  9  X  4J-inches  are  being  used,  a  process  which  gives  a 
side-cut  brick.  An  active  discussion  is  now  going  on  as  to  the 
relative  merits  of  the  resulting  brick;  but  apparently  there  is  no 
material  difference  between  the  two.  The  wTeak  point  of  the  stiff- 
mud  process  is  the  laminations  that  must  inevitably  result  from 
pushing  a  stream  of  clay  through  a  fixed  die.  The  friction  of  the 
sides  of  the  die  will  cause  differential  speeds  in  the  flow  of  the  clay, 
and  these  variations  must  necessarily  result  in  laminations  in  the 
clay  bar.  If  the  air  has  been  expelled  from  the  clay  by  the  pug 
mill,  these  lines  can  be  largely  closed  up  again  by  a  properly 
shaped  die,  and  a  first-class  brick  will  result  in  which  the  lamina- 
tions will  be  inconspicuous  and  of  no  importance;  but  if  the  air 
has  not  been  expelled,  or  if  the  former  and  the  die  are  not  properly 
designed,  there  will  be  a  number  of  concentric  lines  that  divide 
the  cross  section  of  the  brick  into  a  scries  cf  shells  or  concentric 


ART.   1.]  THE   BRICK.  467 

cylinders  which  greatly  weakens  the  brick.  These  laminations 
vary  with  the  character  and  the  condition  of  the  clay;  and  as  a 
rule;  the  more  plastic  the  clay  the  more  prominent  the  laminations. 

722.  Re-pressing.  After  leaving  the  molding  machine,  stiff- 
mud  brick  are  usually  re-pressed.  Re-pressing  makes  the  brick 
more  symmetrical  in  form  and  of  better  appearance,  but  can  not 
increase  its  solidity  or  decrease  the  laminations;  and  it  is  not  certain 
that  re-pressing,  by  breaking  the  original  bond  of  the  clay,  does  not 
decrease  the  strength  and  durability  of  the  brick.  The  effect  of 
re-pressing  upon  the  internal  structure  of  the  brick  varies  with 
the  character  of  the  clay,  the -machine  used  in  molding,  the  method 
of  molding,  and  the  force  used  in  re-pressing.  Experiments  * 
seem  to  show  that  re-pressing  slightly  improves  end-cut  die-molded 
brick,  and  slightly  damages  side-cut  brick.  Re-pressed  brick  are 
more  uniform  in  shape,  and  therefore  make  a  more  even  pavement; 
and  for  this  reason  they  may  perhaps  wear  longer.  Re-pressing 
costs  about  2  cents  a  square  yard  of  pavement,  and  its  economic 
value  is  not  yet  established. 

After  being  molded,  or  after  being  re-pressed,  the  brick  are 
placed  on  trucks  or  cars,  and  conveyed  to  the  dry  house.  Thor- 
ough drying  greatly  facilitates  the  burning  of  the  brick. 

723.  Burning.  Paving  brick  are  usually  burned  in  down- 
draft  brick-ovens  having  fire  pockets  or  furnaces  built  in  their 
outer  walls.  The  bottoms  of  the  kilns  are  perforated  to  allow  the 
gases  to  pass  through  the  flues,  which  are  beneath  the  floor,  and 
which  lead  to  the  chimney.  The  fire  passes  up  from  the  furnaces 
into  the  kilns,  then  down  through  the  brick  to  be  burned  to  the 
flues,  and  thence  to  the  chimney.  The  burning  is  the  most  critical 
step  in  the  manufacture  of  paving  brick.  At  first  the  heat  is 
applied  slowly  in  order  to  drive  off  the  water,  without  cracking  the 
brick,  which  contain  from  20  to  30  per  cent  after  being  dried.  A 
low  heat  is  continued  until  the  smoke  passing  off  shows  no  further 
signs  of  steam  or  "water-smoke,"  after  which  the  fires  are  gradu- 
ally increased  until  the  temperature  throughout  the  kiln  is  suffi- 
cient to  vitrify  the  brick.     Most  shales  vitrify  at  from  1,500°  to 

*Prof.  Edward  Qifcm,  Jr.,  p.  100-06  of  Report  of  the  Paving  Brick  Commission 
of  the  National  Brick  Manufacturers'  Association.  T.  A.  Randall  &  Co.,  Indian- 
apolis, Ind.,  1897. 


468  BRICK   PAVEMENTS.  [CHAP.   XIV. 

2,000°  F.;  but  impure  fire-clays  require  from  1,800°  to  2,300°  F. 
From  seven  to  ten  days  are  required  to  raise  the  entire  kiln  to  the 
vitrifying  temperature. 

There  has  been  much  discussion  as  to  the  meaning  of  the  term 
vitrification  as  applied  to  brick  making.  Literally  speaking,  to 
vitrify  means  to  render  glassy;  but  as  applied  to  clay  working, 
vitrification  has  come  to  mean  incipient  fusion  of  the  particles  of 
the  clay  into  a  new  chemical  compound.  The  degree  of  vitrification 
increases  with  the  temperature,  and  the  logical  end  of  the  process 
is  complete  fusion.  A  clay  is  partially  vitrified  if  its  constituents 
have  begun  to  unite  by  heat  into  a  compound  silicate,  even  though 
it  may  not  have  a  glassy  fracture.  The  physical  peculiarities 
which  mark  vitrification  in  a  burnt  clay  are  the  conchoidal  frac- 
ture, the  absence  of  pores,  and  the  blending  of  the  ingredients  into 
one  mass.  Cracks,  fissures,  and  cavities  may  be  found,  but  porosity 
must  not  exist  in  a  well  vitrified  brick,  and  the  original  particles 
must  have  begun  to  cohere  by  the  bond  of  heat  instead  of  the  bond 
of  plasticity.  Within  limits  the  degree  of  vitrification  in  a  burned 
clay  is  measured  by  its  ability  to  absorb  water.  A  lightly  burned 
brick  will  greedily  asborb  water,  and  the  greater  the  degree  of 
vitrification  the  less  the  water  absorbed,  a  perfectly  vitrified  brick 
absorbing  absolutely  no  water. 

After  the  bricks  have  been  vitrified  entirely  through,  the  kiln  is 
tightly  closed  and  allowed  to  cool  very  slowly.  Rapid,  cooling 
renders  the  brick  brittle;  but  by  slow  cooling  they  are  annealed 
and  rendered  tough.  Slow  cooling  is  the  secret  of  toughness,  and 
the  slower  the  cooling  the  tougher  the  brick.  The  annealing  is 
frequently  unduly  hurried,  much  to  the  detriment  of  the  toughness 
of  the  brick.  The  kiln  is  often  cooled  in  three  to  five  days,  when 
seven  to  ten  would  materially  improve  the  product  and  usually 
would  be  worth  the  extra  cost. 

With  the  utmost  care  a  considerable  per  cent  of  the  contents 
of  the  kiln  are  unsuitable  for  paving  purposes,  because  of  some 
being  under-burned  and  some  over-burned.  With  shale  70  to  80 
per  cent  of  first-class  paving  brick  is  a  high  average,  while  with 
impure  fire  clay  80  or  90  per  cent  may  be  produced. 

724.  Size  of  the  Brick.  Formerly  there  was  considerable  differ- 
ence of  opinion  as  to  the  best  size  for  paving  brick,  some  advocating 


ART.   1.]  THE   BRICK.  469 

2"  x  4"  X  8",  others  3"  X  4"  X  9",  and  a  few  4"  X  5"X  12". 
The  first  is  known  as  a  brick  and  the  last  two  as  paving  blocks. 
It  was  often  claimed  that  one  or  the  other  size  made  the  better 
pavement,  but  there  is  no  material  difference  in  the  quality  of  the 
pavement  between  the  different  sizes,  except  that  possibly  the 
block  may  be  a  little  more  durable. 

725.  The  advantages  of  the  building-brick  size  are:  (1)  being 
smaller  they  are  more  easily  vitrified,  and  therefore  a  little  cheaper 
to  manufacture;  and  (2)  brick  unsuitable  for  use  in  the  pavement 
can  be  more  readily  disposed  of  for  building  purposes,  a  fact  which 
tends  to  cheapen  the  cost  of  the  brick  used  in  the  pavement.  The 
advantages  of  the  block-size  to  the  manufacturer  are  that  there 
are  fewer  pieces  to  handle ;  and  in  the  pavement  the  blocks  chip  or 
spall  on  the  edges  less  than  the  bricks,  particularly  if  the  filler  is 
not  rigid  (see  §  773).  The  manufacturer  of  the  block  usually  places 
building  brick  in  that  part  of  the  kiln  in  which  it  is  difficult  to  burn 
blocks  thoroughly  (the  bottom  of  a  down-draft  kiln),  a  process 
which  decreases  the  per  cent  of  blocks  unsuitable  for  paving  pur- 
poses, and  at  least  partially  eliminates  the  second  advantage  of  the 
building-brick  size  as  above.  In  the  early  history  of  brick  paving, 
bricks  were  most  in  favor;  but  now  the  blocks  are  most  common. 
Apparently  the  introduction  of  the  blocks  is  due,  at  least  in  part, 
to  the  fact  that  in  the  ordinary  method  of  testing  the  bricks  or 
blocks  by  tumbling  in  a  cylinder  (§  740),  the  bricks  lose  a  greater 
per  cent  of  their  weight  than  do  the  blocks,  and  consequently 
manufacturers  preferred  to  submit  blocks  rather  than  bricks  for  a 
competitive  test,  particularly  as  in  the  early  history  of  testing 
clay  paving-material  specifications  made  no  distinction  between 
bricks  and  blocks  in  the  loss  permissible  (§  748). 

Unfortunately  the  size  of  building  bricks  and  also  of  paving 
blocks  varies  considerably  in  different  parts  of  the  country.  Uni- 
formity of  size  is  very  desirable  for  convenience  in  making  re- 
pairs. Sizes  of  bricks  and  blocks  range  all  the  way  from  2x4x8 
inches  to  4  X  5  X  10  inches,  but  the  maximum  is  seldom  more  than 
3X4X9  inches.  There  is  no  conventional  line  by  which  to 
distinguish  bricks  from  blocks;  but  as  a  rule  "paving  brick"  are 
about  2\"  X  4"  X  8£"  and  "  paving  blocks  "  3"  X  4"  X  9". 

726.  Form  of  the  Brick.     Early  in  the  history  of  the  paving- 


470  BRICK  PAVEMENTS.  [CHAP.  XIV. 

brick  industry  a  number  of  odd  shapes  were  upon  the  market,  but 
they  have  all  been  abandoned;  and  at  present  the  only  variations 
from  the  form  having  flat  sides  and  square  corners  are:  (1)  rounded 
corners,  to  prevent  chipping;  (2)  grooves  on  the  sides  and  endsr 
to  increase  the  holding  power  of  the  material  used  to  fill  the  joints 
between  the  bricks  (§  773);  and  (3)  raised  letters  or  buttons  on  the 
side,  to  hold  the  bricks  apart  to  facilitate  the  introduction  of  the 
joint  filler. 

727.  Rounded  corners  are  very  common,  the  radius  of  the  corner 
varying  from  one  to  three  eighths  of  an  inch.  The  rounding  of  the 
corner  decreases  the  loss  during  the  first  part  of  the  test  of  the  brick 
in  the  rattler  (§  740)  and  also  diminishes  the  chipping  during  its 
earlier  use  in  the  pavement;  but  the  rounded  corner  increases  the 
initial  roughness  of  the  pavement,  and  makes  it  at  the  beginning 
what  it  would  otherwise  have  become  only  after  a  considerable 
use,  if  ever.  The  rounded  corner  is  a  disadvantage,  whatever  the 
material  with  which  the  joint  is  filled  (§  773),  since  it  gives  a  thin 
edge  to  the  filling  which  easily  crumbles  or  chips  off.  The  intro- 
duction of  the  rounded  corner  was  due,  in  part  at  least,  to  the  desire 
of  the  manufacturer  to  make  a  brick  that  would  more  readily  pass 
the  usual  rattler  test;  and  if  this  test  had  consisted  in  determining 
the  loss  in  a  certain  number  of  revolutions  after,  say,  an  initial  500 
revolutions,  this  tendency  would  probably  not  have  occurred.  The 
corner  is  usually  rounded  during  the  re-pressing,  which  disturbs 
the  initial  bond  of  the  clay  and  weakens  the  brick,  the  amount  of 
this  weakening  varying  with  the  amount  of  the  disturbance  and 
with  the  character  of  the  clay.  The  round  corner  is  of  doubtful 
value. 

728.  Fig.  122,  123,  and  124  shows  three  forms  of  the  grooves.' 
employed  to  facilitate  the  introduction  of  the  joint  filler  and  tc 
increase  its  holding  power.  The  depth  of  the  groove  differs  with 
the  maker,  but  is  usually  about  -j  to  y\  inch  deep.  The  arrange- 
ment of  the  grooves  in  Fig.  122  is  quite  objectionable,  since  the 
brick  spalls  off  from  the  edge  down  to  the  groove,  particularly  when 
the  joints  are  filled  with  sand.  The  form  shown  in  Fig.  123  is. 
better  than  that  in  Fig.  122,  since  the  vertical  grooves  facilitate 
the  introduction  of  the  joint  filler.  It  would  be  still  better,  if  the 
vertical  grooves  were  continuous  across  the  face  of  the  brick.     The 


ART.    1.] 


THE    BRICK. 


471 


form  shown  in  Fig.  124  is  perhaps  a  little  less  objectionable  than 
that  in  either  Fig.  122  or  123.  All  three  of  the  preceding  forms 
often  have  the  name  of  the  manufacturer  in  sunken  letters  in  the 
sides  of  the  brick — partly  for  advertising  purposes  and  partly  to 
increase  the  holding  power  of  the  material  used  to  fill  the  joints0 
The  grooves  and  also  the  sunken  letters  are  added  in  re-pressing? 


Fig.  122.— Grooved  Paving  Blocks. 


Fig.  123.— Grooved  Paving  Blocks. 


Fig.  124.— Grooved  Paving  Blocks. 


a  process  which  breaks  the  original  bond  of  the  clay — at  least  to 
some  extent, — and  therefore  weakens  the  brick. 

One  object  of  the  grooves  is  to  facilitate  the  introduction  of 
the  joint  filler.  Practically  the  only  materials  employed  to  fill 
the  joints  are  sand,  tar,  and  hydraulic  cement;  and  no  difficulty 
is  experienced  (when  proper  methods  are  employed — see  §  773) 
in  filling  the  joints  with  any  of  these  materials. 

Another  object  of  the  grooves  and  of  the  sunken  letters  is  to 
obtain  a  keying  or  locking  action  of  the  joint  filling;  but  it  does  not 
appear  that  this  is  either  needed  or  does  any  good.  The  resistance 
to  shearing  of  the  portion  in  the  grooves  is  small  in  comparison  with 
the  adhesion  of  the  joint-filling  material  to  the  side  of  the  brick. 

729.  The  raised  letters  or  buttons  are  to  facilitate  the  introduc- 
tion of  the  joint  filler;  but  with  the  most  regular  re-pressed  paving 
blocks  or  bricks  the  joints  when  the  bricks  are  laid  as  close  as  possi- 


47.2  BRICK   PAVEMENTS.  [CHAP.  XIV. 

ble  are  always  sufficiently  open  to  permit  the  introduction  of  the 
joint  filler.  Needlessly  wide  joints  are  objectionable,  since  the  ma- 
terial used  in  filling  the  joints  is  not  likely  to  be  as  durable  as  the 
brick  itself,  and  hence  the  thinner  the  joints  the  better.  With 
bricks  having  a  wearing  face  3X9  inches  and  joints  J  inch  wide, 
the  joints  constitute  5  per  cent  of  the  surface  of  the  pavement, 
and  J-inch  joints  will  occupy  10  per  cent  of  the  surface. 
I  730.  The  value  of  the  grooves  and  of  the  recessed  letters,  as  also 
of  the  raised  letters  and  buttons,  can  be  better  understood  after 
the  consideration  of  the  purposes  of  filling  the  joints  and  of  .he  ma- 
terials used — see  §  773-80. 

731.  REQUISITES  FOR  PAVING  BRICK.  The  brick  should 
be  reasonably  perfect  in  shape,  should  be  free  from  marked  warp- 
ing or  distortion,  and  should  also  be  uniform  iii  size,  so  as  to  fit 
closely  together  and  make  a  smooth  pavement.  A  good  paving 
brick  should  be  hard  so  as  to  resist  the  crushing  action  of  the 
wheels  of  vehicles,  and  tough  so  as'  to  resist  the  abrading  action 
of  traffic.  Any  particular  brick  should  be  homogeneous  in  texture 
and  should  be  free  from  lamination  or  seams,  so  as  to  wear  uni- 
formly; and  all  the  brick  used  in  a  pavement  should  be  of  the  same 
grade  so  that  the  pavement  may  wear  evenly. 

732.  TESTING  THE  BRICK.  It  is  important  to  have  a  definite 
method  of  testing  the  qualities  of  any  artificial  material,  since  then 
all  parties  may  know  exactly  the  grade  called  for,  and  since  the 
results  obtained  by  different  observers  with  different  materials  may 
be  compared.  This  is  particularly  true"  of  brick,  since  the  clays 
differ  greatly  in  quality  and  also  since  a  slight  variation  in  each  step 
of  the  manufacture  materially  affects  the  result.  Definite  methods 
of  testing  paving  brick  are  less  than  ten  years  old,  and  probably 
the  best  method  has  not  yet  been  discovered;  but  in  the  past  five 
years  methods  have  been  developed  which  give  fairly  satisfactory 
and  definite  results.  Several  tests  formerly  employed  have  now 
been  practically  abandoned ;  but  for  the  sake  of  completeness  these 
will  be  briefly  considered.  The  object  of  testing  paving  brick  is 
two-fold:  (1)  to  determine  whether  the  material  is  suitable  for 
use  in  a  pavement;  and  (2)  to  enable  comparisons  to  be  made 
between  different  classes  of  brick. 

733.  General  Appearance.    A  critical  examination  of  a  paving 


ART.   1.]  THE    BRICK.  473 

brick  by  the  experienced  eye  aided  by  a  hand  hammer  is  an  excel- 
lent method  of  determining  the  relative  merits  of  different  bricks 
of  a  particular  kind;  but  unfortunately  experience  with  one  make 
is  not  of  much  value  with  brick  made  by  a  different  process  or  of  a 
different  kind  of  clay,  and  further  the  results  by  this  method  of 
testing  admits  of  no  numerical  evaluation  or  even  of  being  described 
accurately.  It  is  a  method  of  selecting  or  inspecting  rather  than 
of  testing. 

The  brick  should  have  reasonably  flat  sides  and  square  corners. 
They  should  be  nearly  uniform  in  size,  since  the  unduly  large  size 
indicates  under-burned  or  soft  brick,  and  the  unduly  small  size 
usually  indicates  over-burned  or  brittle  brick.  However,  as  most 
paving  brick  are  die-molded  and  as  the  die  wears  larger  by  use  and 
must  ultimately  be  replaced  by  a  new  one,  a  change  of  size  from 
this  cause  must  not  be  confused  with  that  due  to  deficient  or  ex- 
cessive burning.  The  edges  of  the  brick  should  be  smooth  and  free 
from  serrations  or  "ragging/'  due  to  friction  in  the  die;  and  the 
"  kiln  marks,"  or  impressions  from  the  over-lying  brick  in  burning, 
should  not  be  over  one  eighth  of  an  inch.  The  quality  of  the  brick 
can  be  judged  by  striking  it  a  sharp  blow  with  a  hand  hammer,  or 
by  striking  two  together,  or  by  dropping  the  flat  side  of  one  upon 
another. 

The  interior  of  the  brick  should  be  homogeneous,  free  from 
uncrushed  or  lumpy  material,  especially  if  such  material  is  not 
united  by  vitrification  with  the  balance  of  the  material  of  the 
brick.  The  brick  should  be  vitrified  clear  through  to  the  center; 
and  should  contain  neither  unfused  spots,  which  indicate  sand  or 
fire  clay,  nor  glassy  or  spongy  spots,  which  indicate  imperfect 
crushing  and  mixing  of  some  fusible  mineral  in  the  clay.  The 
structure  should  be  free  from  "shakes"  or  marked  laminations. 
Fire  cracks,  caused  by  too  rapid  firing,  if  small  and  superficial,  are 
not  of  much  importance;  but  they  should  be  limited  in  number 
and  extent.  There  should  be  no  lumps  of  lime,  due  to  the  presence 
of  limestone  pebbles  in  the  unburned  clay,  since  these  will  slake 
when  the  brick  becomes  wet  and  probably  disrupt  it. 

734.  Color.  The  color  is  no  criterion  of  the  value  of  a  paving 
brick,  when  comparing  brick  of  various  makes;  but,  in  inspecting 
brick  from  a  single  factory,  the  color  will  usually  furnish  a  fairly 


474  BRICK    PAVEMENTS.  [CHAP.   XIV. 

safe  guide  as  to  the  relative  hardness,  when  the  inspector  is  thor- 
oughly acquainted  with  the  particular  manufacture.  The  knowl- 
edge gained  regarding  the  relation  of  color  and  quality  in  inspecting 
one  make  of  brick,  however,  can  seldom  be  used  with  that  of  another 
make  from  a  different  locality,  as  clays  vary  greatly  in  kind  and 
degree  of  color.  The  popular  belief  is  that  hardness  is  proportional 
to  the  darkness  of  the  color  of  the  brick,  and  that  light  color  is  prima 
facie  evidence  of  softness.  As  a  rule  the  impure  fire  clays  make 
excellent  paving  material,  although  the  brick  are  light  colored, 
usually  buff,  wrhile  shale  brick  are  red  or  brown.  For  a  particular 
clay,  the  color  of  the  bricks  indicates  the  degree  of  heat  they  have 
received,  provided  they  were  burned  with  the  same  fuel  and  \mdei 
the  same  conditions;  and  ordinarily  the  higher  the  heat  the  darker 
the  color,  and  presumably  the  better  the  brick.  The  uniformity 
of  the  color  of  the  interior  of  the  brick  is  more  important  than  the 
color  of  the  exterior. 

The  color  of  the  outside  of  the  brick  is  sometimes  valueless 
owing  to  the  sand  employed  to  prevent  sticking  in  the  kiln,  or  to 
the  effect  of  sulphur  in  the  coal  used  in  burning,  or  to  salt  glazing. 
Salt  glazing  is  a  trick  occasionally  employed  to  give  a  dark  gloss 
to  the  outside  which  is  very  attractive  to  the  superficial  observer, 
but  wThich  is  practically  worthless,  since  it  is  only  skin  deep  and 
soon  wears  off.  Salt  glazing  makes  it  more  difficult  to  detect  soft 
brick,  and  should  never  be  allowed  on  paving  brick. 

735.  Specific  Gravity.  In  a  general  way,  the  more  dense  a  brick 
the  harder  and  stronger  it  is;  and  consequently  early  in  the  history 
of  brick  testing  it  was  believed  that  a  knowledge  of  the  specific 
gravity  would  be  of  value  in  judging  of  the  quality  of  a  paving 
brick.  It  is  now  known  that  the  specific  gravity  reveals  nothing 
not  determined  by  other  tests;  and  further  that  the  density  depends 
upon  the  character  of  the  clay,  the  kind  of  fuel,  etc.,  and  in  no  way 
measures  the  quality  of  the  product.  The  specific  gravity  may  be 
computed  by  the  formula : 

Q      .        '      .+  Wa 

Specific  gravity  =  Ws_wi> 

in  which  W  a  represents  the  weight  of  the  dry  brick  in  air  W  s  the 
weight  of  the  saturated  brick  in  air,  Wi  the  weight  of  the  brick 


ART.  1.]  THE   BRICK.  475 

immersed  in  water.  The  specific  gravity  of  shale  brick  ranges 
from  2.05  to  2.55,  and  usually  from  2.20  to  2.40;  and  that  of  brick 
made  from  impure  fire  clay  ranges  from  1.95  to  2.30,  and  generally 
from  2.10  to  2.25. 

736.  Crushing  Strength.  The  results  for  the  crushing  strength 
vary  more  with  the  details  of  the  method  employed  than  any  other 
test  of  paving  brick.  There  is  no  standard  method  of  making  this 
test.  (1)  Some  experimenters  test  cubes,  others  half  brick,  and  still 
others  whole  brick;  (2)  some  grind  the  pressed  surfaces  accurately 
to  planes,  some  true  the  surface  up  by  putting  on  a  thin  coat  of  plas- 
ter of  paris,  while  still  others  level  up  with  blotting  paper,  card 
board,  etc.;  (3)  some  test  the  brick  on  end,  some  on  edge,  and 
others  flatwise.  For  experimental  data  showing  the  marked 
effect  of  the  different  methods  of  testing,  see  the  author's  Treatise 
on  Masonry  Construction,  page  41-45. 

Tests  on  cubes  cut  from  paving  brick  show  that  the  best  paving 
brick  have  a  crushing  strength  of  10,000  to  20,000  pounds  per  square 
inch.  This  is  the  crushing  strength  when  the  load  is  applied  uni- 
formly over  the  surface  of  the  test  specimen;  but  if  the  pressure 
is  applied  to  only  a  small  part  of  the  upper  surface  of  a  brick,  the 
strength  will  be  much  greater.*  Any  brick  that  is  likely  to  be 
accepted,  for  paving  purposes  by  any  of  the  tests  hereafter  de- 
scribed, is  in  no  danger  of  being  crushed  by  the  pressure  of  the  wheel 
of  a  vehicle.  For  example,  the  surface  of  contact  between  a  wheel 
having  a  1^-inch  tire  loaded  with  half  a  ton  is  about  one  half  square 
inch,  which  gives  a  pressure  on  the  brick  of  only  about  2;000  pounds 
per  square  inch. 

If  the  crushing  strength  could  be  easily  and  accurately  found, 
it  would  be  of  value  in  determining  the  relative  strength,  and  hence 
would  be  useful  in  comparing  the  quality  of  different  brick;  but 
owing  to  the  difficulty  of  making  the  experiments  and  to  the  un- 
certainty of  the  results,  the  test  has  been  abandoned. 

737.  Absorption  Test.  In  the  early  days  of  the  paving  brick 
industry,  many  of  the  brick  used  were  so  porous  and  brittle  that  it 
was  feared  they  would  be  disintegrated  by  the  action  of  frost;  and 
consequently  the  absorption  test  was  employed  to  eliminate  porous 

*  See  Baker's  Masonry  Construction,  p.  190, 


476  BKICK    PAVEMENTS.  [CHAP.   XIV, 

brick.  Subsequent  tests  by  repeatedly  freezing  and  thawing  paving 
bricks  showed  that  any  brick  which  was  likely  to  be  accepted  for 
paving  purposes  would  not  be  appreciably  injured  by  the  action 
of  frost.  There  are  probably  two  elements  that  prevent  frost 
from  seriously  injuring  even  a  soft  paving  brick;  viz.:  (1)  the 
cushioning  effect  of  the  air  remaining  in  the  pores  of  the  brick,  and 
(2)  the  strength  of  the  brick  may  be  greater  than  the  disrupting 
effect  of  the  frost.  Alternate  freezing  and  thawing  might  injure 
a  non-vitrified  brick,  which  is  not  only  very  porous  but  is  also  defi- 
cient in  strength;  but  such  a  brick  would  be  rejected  for  paving 
purposes  as  the  result  of  a  casual  inspection.  The  absorption  test 
is  no  longer  regarded  of  importance  as  measuring  the  ability  of  the 
brick  to  resist  freezing  and  thawing. 

The  absorptive  power  of  a  brick  is  now  regarded  only  as  a 
measure  of  the  porosity  of  the  brick,  i.  e.,  of  the  degree  of  vitrifica- 
tion. In  the  first  stages  of  burning,  free  water  is  driven  off  With 
no  perceptible  effect  upon  the  clay;  in  the  second  stage,  the  water 
of  constitution  of  the  clay  is  expelled,  leaving  the  clay  in  a  very 
porous  and  spongy  condition.  At  this  time  the  strength  of  the 
clay  is  at  its  lowest  point,  and  the  porosity  is  at  its  greatest  devel- 
opment ;  while  the  chemical  combination  between  the  clay  and  the 
other  minerals  has  not  yet  begun.  The  partially  burned  brick  can 
be  easily  crushed  to  a  powTder;  and  if  wetted  and  frozen,  it  be- 
comes a  mass  of  gritty  mud  on  thawing.  But  if  the  temperature 
of  burning  is  increased,  the  clay  decreases  in  porosity  and  increases 
in  strength;  and  the  walls  of  the  pores  fuse  and  close  in  on  one 
another,  gradually  expelling  the  gases  which  filled  them  and  oblit- 
erating the  original  porous  structure.  As  the  cell  walls  collapse  and 
tend  to  expel  the  gases  from  the  pores,  these  gases  encounter  increas- 
ing difficulty  in  finding  their  way  out  to  the  surface ;  and  some  of 
these  gases  become  imprisoned  in  the  clay,  and  as  the  latter  becomes 
more  and  more  fluid  or  viscous  with  the  rising  heat  these  volumes 
of  gases  expand  and  create  little  spherical  cavities  or  vesicles  in 
the  clay  body.  So  it  always  happens  that  in  burning  a  piece  of 
clay-ware  two  opposing  forces  are  at  work  at  the  conclusion  of  the 
burning.  One  is  the  obliteration  of  the  pore  structure, '  accom- 
panied by  the  expulsion  of  the  gases,  which  produces  greater  density 
and  strength ;  and  the  other  is  the  expansion  of  imprisoned  volumes 


ART.   1.]  THE   BRICK.  477 

of  gases,  which  produce  a  cindery  or  vesicular  structure,  and  de- 
creases the  density  and  strength.  Therefore  there  is  a  point  of 
maximum  strength,  and  continuing  the  burning  beyond  this  de- 
creases the  porosity  and  also  the  strength.  In  the  early  history 
of  the  paving-brick  industry,  it  was  held  that  the  less  the  absorp- 
tion the  better  the  brick;  but  the  above  explanation  shows  that 
there  is  a  degree  of  porosity  corresponding  to  maximum  strength. 
The  relation  between  strength  and  porosity  varies  greatly  with 
the  character  of  the  clay  and  with  the  method  of  molding.  For 
example,  a  stiff-mud  shale  brick  has  an  absorption  of  4  per  cent 
and  disrupts  under  the  action  of  frost;  while  a  soft-mud  brick 
made  of  surface  clay  will  endure  with  an  absorption  of  10  or  12 
per  cent.* 

Different  bricks  vary  widely  in  their  rate  of  absorption.  For 
example,  one  brick  absorbed  in  one  day  80  per  cent  of  its  total 
amount,  while  another  absorbed  only  8.7  per  cent;  and  two  other 
specimens  absorbed  71.8  and  19.5  per  cent  respectively  in  the  same 
time.t  The  absorption  of  whole  brick  is  slightly  less  than  that  of 
half  brick,  and  the  absorption  of  half  brick  is  considerably  less  than 
that  of  small  chips.  For  the  above  reasons  and  for  other  minor  ones, 
results  for  the  absorptive  power  are  likely  to  be  untrustworthy. 

738.  The  absorption  test  is  capable  of  giving  data  of  value  in 
regard  to  the  degree  of  vitrification,  but  to  be  generally  useful  as  a 
standard  for  grading  brick  the  limiting  per  cent  of  absorption 
should  be  determined  for  each  variety  of  brick,  a  task  which  is 
impracticable,  except  where  there  are  only  a  few  brands  of  brick 
upon  any  particular  market. 

Hence  this  test  is  valuable  to  a  user  of  brick  only  as  a  check 
upon  the  uniformity  of  a  particular  brand.  It  could  be  used  to 
exclude  any  soft  and  porous  brick,  but  such  material  would  be  un- 
hesitatingly rejected  on  account  of  its  general  appearance. 

The  National  Brick  Manufacturers'  Association  recommend 
that  when  this  test  is  employed,  it  be  made  according  to  the  follow- 
ing method :  % 

♦Report  of  Paving  Brick  Commission  of  National  Brick  Manufacturers' Associa- 
tion, p.  62-63.    T.  A.  Randall  &  Co.,  Indianapolis,  Ind. 
fTWcL,  p.  70,  Table  XX. 
%  Ibid  ,  p.  830 


478  BRICK   PAVEMENTS.  [CHAP.   XIV. 

"1.  The  number  of  bricks  constituting  a  sample  for  an  official 
test  shall  be  five. 

"  2.  The  bricks  selected  for  conducting  this  test  shall  be  such  as 
have  been  previously  exposed  to  the  rattler  test.  If  such  are  not 
available,  then  each  whole  brick  must  be  broken  in  halves  before 
the  test  begins. 

"  3.  The  bricks  shall  be  dried  for  forty-eight  hours  continuously, 
at  a  temperature  of  230  to  250  degrees  Fahr.,  before  the  absorption 
test  begins. 

"  4.  The  bricks  shall  be  weighed  before  wetting,  and  shall  then 
be  completely  immersed  for  forty-eight  hours. 

"  5.  After  soaking,  and  before  re-weighing,  the  bricks  must  be 
wiped  till  free  from  surplus  water  and  practically  dry  on  the  surface. 

"  6.  The  samples  must  then  be  re-weighed  at  once.  The  scales 
must  be  sensitive  to  one  gram. 

"  7.  The  increase  in  weight,  due  to  absorption,  shall  be  calcu- 
lated in  per  cents  of  the  dry  weight  of  the  original  bricks." 

Shale  paving  bricks  when  tested  as  above  usually  show  less 
than  2  per  cent  of  absorption,  some  of  the  best  ranging  from  0.75 
to  1.50;  less  than  0.5  probably  indicates  •  an  over-burned  and 
brittle  brick.  Good  paving  brick  made  of  impure  fire  clay  rarely 
absorb  less  than  2.5  per  cent,  and  often  over  5  per  cent. 

To  apply  this  test  to  determine  uniformity  of  quality,  it  will 
be  necessary  to  establish  limits  of  the  absorption.  This  may  be 
done  by  inserting  in  the  specifications  a  clause  somewhat  like  the 
following :  * 

' l  At  the  time  of  submitting  bids,  the  bidder  shall  furnish  twenty- 
five  bricks  of  the  make  specified  in  his  bid,  on  which  a  rattler  test 
and  an  absorption  test  shall  be  made.  A  requirement  of  the  bricks 
furnished  for  the  pavement  will  be  that  their  absorption  tests  shall 
fall  within  the  following  limits:  When  the  result  of  the  absorption 
test  of  the  sample  bricks  is  below  2  per  cent,  the  limits  shall  be  } 
per  cent  less  and  1  per  cent  more  than  the  sample;  when  between 
2  per  cent  and  5  per  cent,  the  limits  shall  be  1  per  cent  less  and  1^- 
per  cent  more  than  the  sample." 


♦Report  of  Committee  on  Brick  Tests  and  Specifications,  Proc  Illinois  Society 
of  Engineers,  1901,  p.  90. 


ART.   1.]  THE    BRICK.  479 

739.  Transverse  Strength.  This  is  determined  by  resting  the 
brick  upon  two  knife-edges  and  applying  a  steady  pressure  on  the 
upper  side  of  the  brick  through  a  third  knife-edge  placed  midway 
between  the  other  two.  The  results  are  expressed  in  terms  of  the 
modulus  of  rupture,  which  is  computed  by  the  following  formula; 

K  "  2  b  d2 

in  which  R  represents  the  modulus  of  rupture  in  pounds  per  square 
inch,  W  the  breaking  load  in  pounds,  I  the  distance  between  sup- 
ports in  inches,  b  the  breadth  of  the  brick  in  inches,  and  d  the  depth 
of  the  brick  in  inches.  The  brick  may  be  tested  edgewise  or  flat- 
wise, although  the  former  is  usually  the  better  method,  since  then 
W  is  larger.  The  knife-edges  should  be  rounded  transversely  to 
a  radius  of  about  one  sixteenth  of  an  inch  and  longitudinally  to  a 
radius  of  about  12  inches,  to  secure  better  contact  and  to  prevent 
the  brick  from  being  crushed  at  the  edges.  Some  authorities 
recommend  grinding  opposite  edges  of  the  brick  to  parallel  planes, 
but  this  is  a  useless  expense.  If  the  brick  is  warped,  the  contact 
between  the  brick  and  the  knife-edges  can  easily  be  made  entirely 
satisfactory  by  placing  pieces  of  metal  under  the  blocks  carrying 
the  lower  knife-edges,  or  by  shifting  the  brick  longitudinally,  or  by 
turning  it. 

The  modulus  of  rupture  of  bricks  that  have  given  excellent 
service  in  a  pavement  varies  from  1,500  to  3,500  pounds  per  square 
inch,  usually  from  2,000  to  3,000.  Owing  to  apparently  unavoid- 
able variations  in  the  structure  of  the  brick  it  is  not  possible  to 
attain  closely  concordant  results  in  making  this  test;  and  with 
the  utmost  care  in  selecting  the  brick  and  in  making  the  tests,  the 
variation  from  the  mean  ranged  from  8  to  30  per  cent,  and  on  the 
average  was  about  20  per  cent.* 

The  cross-breaking  test  furnishes  a  means  of  comparing  the 
toughness  of  various  kinds  of  paving  brick.  The  uniformity  of 
the  results  for  any  particular  kind  of  brick  indicates  its  structural 
soundness,  freedom  from  air  checks,  etc.,  and  shows  whether  the 

*  Report  of  Paving  Brick  Commission,  p.  90,  Table  XXXII. 


480  BRICK   PAVEMENTS.  [CHAP.  XIV 

material  has  been  properly  treated  in  the  various  stages  of  manu- 
facture. The  transverse  strength  indicates  the  resistance  of  the 
brick  to  cross  breaking  when  laid  in  the  pavement  on  an  unyield- 
ing and  uneven  surface ;  but  this  element  is  not  entitled  to  much 
consideration  since  brick  are  seldom  thus  broken  in  the  pave- 
ment, at  least  not  until  nearly  worn  out. 

The  test  is  comparatively  easy  to  make,  and  is  a  valuable  check 
upon  the  rattler  test  (§  740). 

740.  Impact  and  Abrasion  Test.  This  test  is  made  by  rolling 
or  tumbling  the  brick,  with  or  without  pieces  of  iron,  in  a  foundry 
rattler  or  revolving  cast-iron  barrel.  This  test  is  often  called  the 
rattler  test.  It  is  the  crucial  test  of  a  paving  brick  and  greatly 
exceeds  in  importance  all  the  other  tests  combined.  It  is  pre- 
eminently the  test  that  will  show  whether  a  brick  will  prove  sat- 
isfactory in  service,  and  which  of  two  or  more  samples  will  be  the 
more  enduring  in  the  pavement.  This  test  imitates  more  closely 
than  any  other  the  impact  due  to  the  horse's  hoofs  and  shoes,  and 
to  the  bumping  of  the  vehicle  wheels,  and  also  the  abrasion  due  to 
the  slipping  of  the  horse's  feet  and  the  sliding  of  the  wheels.  The 
tumbling,  rolling,  and  sliding  of  the  brick  and  iron  over  each  other 
rapidly  wear  off  the  brick,  and  closely  represents  the  treatment 
a  brick  will  receive  in  the  pavement.  The  result  is  jointly  de- 
pendent upon  the  toughness  of  the  brick— its  ability  to  resist 
shock, — and  its  hardness — its  ability  to  resist  abrasion. 

To  make  this  test  of  any  scientific  value  in  determining  either 
the  probable  behavior  of  the  material  in  the  pavement  or  the  rela- 
tive merits  of  different  brick,  it  is  necessary  to  have  some  standard 
method  of  conducting  the  experiments.  Unless  some  standard  is 
established,  this  method  can  be  employed  only  to  select  the  best  of 
a  number  of  samples  tested  under  exactly  the  same  conditions. 
Several  methods  of  standardizing  this  test  have  been  proposed. 

741.  The  first  attempt  to  standardize  the  rattler  test  was  made 
by  the  author.*  Brick  that  had  seen  service  in  a  pavement  and 
pieces  of  well  known  natural  stones  used  for  paving  purposes, 
together  with  small  pieces  of  scrap  cast-iron,  were  rolled  in  a  rattler. 


♦Durability  of  Paving  Biick,  by  Ira  O.  Baker.     46  p.  5"X8' .    T.  A.  Randall  & 
Co.,  Indianapolis,  Ind.,  1891. 


ART.  1.]  THE  BRICK.  431 

By  this  method  any  new  paving  brick  could  be  compared  with  an 
absolute  standard  by  securing  samples  of  the  natural  stones  used, 
and  testing  the  brick  and  the  stone  under  similar  conditions. 
Shortly  after  being  proposed,  this  method  was  quite  widely  adopted; 
but  did  not  give  satisfactory  results,  chiefly  because  the  original 
experiments  were  made  with  a  rattler  having  wooden  staves, 
while  subsequent  tests  were  made  with  rattlers  having  cast-iron 
staves.  The  method  was  objectionable  on  account  of  the  trouble 
and  expense  of  preparing  the  test  pieces  of  natural  stone. 

Later  the  author  made  a  series  of  tests  using  2-inch  cubes  of 
brick  and  stone  with  foundry  "stars"  in  a  rattler  having  metal 
sides;  but  it  was  found  that  the  results  varied  so  greatly  with  the 
form,  size  and  speed  of  the  rattler  as  to  make  them  of  no  great  value. 

742.  Orton's  Method.  From  1895  to  1897,  Prof.  Edward  Orton, 
Jr.,  of  the  Ohio  State  University,  under  the  auspices  of  the  Na- 
tional Brick  Manufacturers'  Association,*  conducted  a  very  exten- 
sive series  of  experiments  upon  the  effect  (1)  of  varying  the  form, 
size,  and  speed  of  the  rattler;  (2)  of  varying  the  quantity  of  brick 
in  the  rattler;  (3)  of  successive  periods  of  rattling;  (4)  with  and 
without  miscellaneous  pieces  of  cast  iron;  and  (5)  with  and  without 
blocks  of  natural  stone.  Based  upon  these  experiments  a  series  of 
recommendations  were  made  to  the  National  Brick  Manufacturers' 
Association  which  were  adopted  in  1897f  as  the  standard  method 
of  making  the  impact  and  abrasion  test  of  paving  brick,  and  which 
were  largely  used  for  two  or  three  years.  This  test  was  aban- 
doned because  of  its  failure  to  sufficiently  discriminate  the  good 
and  the  poor  paving  brick,  and  also  because  of  the  great  variation 
of  duplicate  tests.  The  distinguishing  characteristic  of  this  method 
was  that  only  brick  were  placed  in  the  rattling  chamber. 

743.  In  this  method  bricks  or  blocks  equal  to  15  per  cent  of  the 
volume  of  the  rattling  chamber  were  placed  in  the  standard  rattier 
(see  paragraphs  1  and  2,  §  745)  and  revolved  at  the  rate  of  30 
revolutions  per  minute  for  1  hour.  Under  these  conditions  the 
loss  of  good  paving  brick  varied  from  15  to  25  per  cent. 

744.  Talbot's  Method.     From  1895  to  1899  experiments  were 

*  Report  of  Paving  Brick  Commission.    110  p.  6"  X  9".    T.  A.  Randall  &  Co., 
Indianapolis,  Ind.,  1897. 
f  Ibid.,  p.  57-58. 


482  BRICK    PAVEMENTS.  [CHAP.   XIV. 

conducted  at  the  University  of  Illinois  under  the  direction  of  Prof. 
A.  N.  Talbot  to  determine  the  best  composition  of  the  abrasive 
material.*  From  these  experiments  the  conclusion  was  drawn 
that  the  best  results  were  obtained  by  the  use  of  a  mixed  charge 
of  two  sizes  of  cast-iron  blocks  \  the  distinguishing  characteristic 
of  this  method  of  conducting  the  abrasion  and  impact  test  is  the  use 
of  a  charge  of  abrasive  material  composed  of  two  sizes  of  moder- 
ately heavy  cast-iron  blocks.  The  large  blocks  give  chiefly  impact 
and  the  small  ones  principally  abrasion.  The  relative  amount  of 
these  two  forms  of  wear  may  be  varied  by  varying  the  proportion 
of  the  two  sizes.  This  method  has  been  employed  by  a  number 
of  experimenters,  and  it  has  been  shown  conclusively  that  it  is 
superior  to  that  in  which  brick  alone  was  used  in  the  rattler  for 
the  following  reasons:  (1)  it  more  nearly  represents  the  condition 
of  service  in  the  pavement,  (2)  it  gives  more  uniform  results,  and 
(3)  it  is  more  sensitive  in  differentiating  hard  and  soft  brick. 

745.  N.  B.  M.  A.  Standard.  In  February,  1901,  the  National 
Brick  Manufacturers'  Association  modified  its  previous  standard 
(§  742)  by  adopting  Talbot's  form  of  abrasive  material,  and  pub- 
lished X  the  following  specifications  for  the  standard  method  T>f 
conducting  the  rattler  test  of  paving  brick,  which  have  been  widely 
adopted. 

1.  Dimensions  of  the  Machine.  The  standard  machine  shall  be  28 
inches  in  diameter  and  20  inches  in  length,  measured  inside  the  rattling 
chamber.  Other  machines  may  be  used,  varying  in  diameter  between  20 
and  30  inches,  and  in  length  from  18  to  24  inches;  but  if  this  is  done,  a 
record  of  it  must  be  attached  to  the  official  report.  Long  rattlers  must 
be  cut  up  into  sections  of  suitable  length  by  the  insertion  of  an  iron 
diaphragm  at  the  proper  point. 

2.  Construction  of  the  Machine.  The  barrel  may  be  driven  by  trunnions 
at  one  or  both  ends,  or  by  rollers  underneath,  but  in  no  case  shall  a 
shaft  pass  through  the  rattler  chamber.     The   cross  section   of  the  barrel 


♦The  Technograph,  University  of  Illinois,  1895-96,  p.  93-100;  1897-98,  p.  16-23. 
Proc.  Illinois  Society  of  Engineers,  1897,  p.  82-86 ;  1898,  p.  174-76,  p.  181-86 ;  1899, 
p.  232-34 ;  1900,  p.  107-08 ;  1901,  p.  83-91 . 

f  For  the  dimensions  of  the  two  sizes  and  the  proportions  of  each,  see  para- 
graphs 3  and  4,  §  745. 

X  Abridged  Report  of  the  Committee  on  Technical  Investigation ;  an  official  pam- 
phlet, 10  p.  6"x9". 


ART.  1.]  THE   BRICK.  483 

shall  be  a  regular  polygon  having  fourteen  sides.  The  heads  shall  be 
composed  of  gray  cast  iron,  not  chilled  nor  case-hardened.  The  staves 
shall  preferably  be  composed  of  steel  plates,  as  cast  iron  peans  and  ulti- 
mately breaks  under  the  wearing  action  on  the  inside.  There  shall  be  a 
space  of  one  fourth  of  an  inch  between  the  staves  for  the  escape  of  the 
dust  and  small  pieces  of  waste.  Other  machines  may  be  used  having 
from  twelve  to  sixteen  staves,  with  openings  from  one  eighth  to  three 
eighths  of  an  inch  between  staves,  but  if  this  is  done  a  record  of  it  must 
be  attached  to  the  official  report  of  the  test. 

3.  Composition  of  the  Charge.  All  tests  must  be  executed  on  charges 
containing  but  one  make  of  paving  material  at  a  time.  The  charge 
shall  be  composed  of  the  bricks  to  be  tested  and  iron  abrasive  material. 
The  brick  charge  shall  consist  of  that  number  of  whole  bricks  or  blocks 
whose  combined  volume  most  nearly  amounts  to  1,000  cubic  inches,  or  8 
per  cent  of  the  cubic  contents  of  the  rattling  chamber,  (Nine,  ten,  or 
eleven  are  the  number  required  for  the  ordinary  sizes  on  the  market.) 
The  abrasive  charge  shall  consist  of  300  pounds  of  shot  made  of  ordinary 
machinery  cast-iron.  This  shot  shall  be  of  two  sizes,  as  described  below, 
and  the  shot  charge  shall  be  composed  of  one  fourth  (75  pounds)  of  the 
larger  size  and  three  fourths  (225  pounds)  of  the  smaller  size. 

4.  Size  of  the  Shot.  The  larger  size  shall  weigh  about  7£  pounds  and 
be  about  2£  inches  square  and  4£  inches  long,  having  edges  rounded  to 
a  radius  of  about  £  inch.  The  smaller  size  shall  be  1£  inch  cubes, 
weighing  about  seven  eighths  of  a  pound  each,  with  square  corners  and 
edges.  The  individual  shot  shall  be  replaced  by  new  ones  when  they  have 
lost  one  tenth  of  their  original  weight.* 

5.  Revolutions  of  the  Charge.  The  number  of  revolutions  of  the  stand- 
ard test  shall  be  1,800,  and  the  speed  of  rotation  shall  not  fall  below 
28  nor  exceed  30  per  minute.  The  belt  power  shall  be  sufficient  to  rotate 
the  rattler  at  the  same  speed  whether  charged  or  empty. 

6.  Condition  of  the  Charge.  The  bricks  composing  a  charge  shall  be 
thoroughly  dried  before  making  the  test.f 

7.  Calculating  the  Results.  The  loss  shall  be  calculated  in  percent- 
ages  of    the   weight   of    the   dry   brick    composing   the   charge,    and    no 


*  It  has  been  proposed  to  use  chilled  steel  shot,  which  have  practically  no  wear, 
and  thereby  to  save  the  expense  of  re-placing  and  of  frequently  re- weighing  the 
cast-iron  shot. 

j  "  Soft  brick  saturated  with  8  per  cent  of  water  lost  only  67  per  cent  as  much 
as  brick  from  the  same  lot  tested  dry."  It  has  been  clearly  proved  that  dry 
brick  lose  more  than  wet  ones,  but  the  reason  for  this  difference  has  not  been 
established.  It  is  reasonable  to  suppose  that  different  kinds  of  brick  having 
different  percentages  of  absorption  should  have  different  losses  for  different 
degrees  of  moisture. 


484 


BRICK    PAVEMENTS. 


[CHAP.   XIV, 


result  shall  be  considered  as  official  unless  it  is  the  average  of  two  distinct 
and  complete  tests,  made  on  separate  charges  of  brick.* 

746.  Fig.  125  shows  a  common  form  of  the  standard  rattler. 
The  chamber  on  each  side  of  the  partition  is  of  the  standard  form, 
and  consequently  two  lots  of  brick  may  be  tested  at  the  same  time- 
Fig.  126  shows  a  form  of  rattler,  designed  at  Purdue  University, 
which  permits  easy  access  to  the  rattling  chamber  without  the 
trouble  of  removing  a  stave.  The  rattler  is  enclosed  in  a  dust-proof 
case  made  of  sheet  iron  and  having  felt-packed  joints.     A  door 


Fig.  125—  Riehle's  Standard  Rattler. 


in  the  lower  part  of  the  case  provides  for  the  removal  of  a  pan 
which  receives  the  dust  and  chips  from  the  rattler. 

747.  The  per  cent  of  loss  in  the  impact  and  abrasion  test  will 
depend  upon  the  care  employed  in  culling  the  brick  and  in  select- 


*  There  is  considerable  difference  in  practice  as  to  the  method  of  considering 
broken  brick,  some  experimenters  counting  all  pieces  weighing  less  than  1  pound 
as  abraded  material;  while  others  put  the  limit  at  half  a  pound.  The  latter  is. 
apparently  the  more  common. 


ART.   1.] 


THE   BRICK. 


485 


ing  the  samples,  as  well  as  upon  the  character  of  the  brick.  To 
show  the  results  that  may  be  expected,  the  following  data  ob- 
tained by  a  city  in  Ohio  in  the  ordinary  course  of  business  are  given. 
The  samples  were  selected  from  material  after  delivery  upon  the 


Fig.  126.— Purdue  Rattler  for  Testing  Paving  Brick. 


street,  by  a  representative  of  the  city.  The  tests  were  carefully 
made  according  to  the  N.  B.  M.  A.  standard  as  above.  The 
material  was  in  the  form  of  blocks  approximately  3"  X  4"  X  9". 
The  average  of  the  losses  of  fourteen  samples  was  18.97  per  cent, 


486  BRICK   PAVEMENTS.  [CHAP.  XIV. 

the  range  being  from  15.60  to  24.35  per  cent.  The  samples  repre- 
sent some  of  the  best  paving  material  in  Ohio.  Omitting  the  pro- 
duct of  one  manufacturer,  the  average  of  the  losses  was  18.57  per 
cent,  and  the  range  was  from  15.60  to  21.62  per  cent,  the  last  being 
the  loss  of  a  well-known  standard  paving  block.  Of  the  product 
of  the  thirteen  manufacturers,  nine  had  a  loss  of  less  than  20  per 
cent,  seven  less  than  19  per  cent,  four  less  than  18  per  cent,  and 
two  less  than  16  per  cent.  Eleven  lots  of  the  best  grade  of  blocks 
gave  an  average  loss  of  15.60  per  cent  with  a  range  for  the  average 
of  duplicate  tests  from  12.25  to  18.70  per  cent.  Individual  tests 
of  these  blocks  ran  as  low  as  10.3  per  cent,  and  duplicate  tests  of 
samples  selected  by  the  manufacturer  (not  included  above)  gave 
losses  of  11.76  and  11.92  per  cent  respectively.  Ten  samples  of 
the  blocks  having  the  greatest  losses  gave  an  average  of  21.62  per 
cent  with  a  range  from  14.90  to  34.77;  and  samples  selected  by 
the  manufacturer  (not  included  above)  gave  losses  of  11.14  and 
13.73  per  cent  respectively. 

Ten  lots  of  blocks  tested  in  an  Illinois  city  gave  an  average  loss 
of  18.34  per  cent  with  a  range  from  15.4  to  24.6  per  cent;  and, 
omitting  the  largest  result,  the  average  was  17.64  per  cent  with 
a  range  from  15.4  to  21.2  per  cent.  Of  the  ten  kinds  of  blocks, 
two  had  losses  of  less  than  16  per  cent,  four  less  than  18,  six  less 
than  19,  and  eight  less  than  20  per  cent. 

A  few  other  scattering  results  seem  to  show  that  the  above  are 
fairly  representative  of  the  above  localities;  but  these  localities 
are  favored  in  native  material  suitable  for  making  paving  brick 
and  also  in  the  attention  given  to  that  industry,  and  consequently 
other  localities  may  not  expect  as  favorable  results.  The  Second 
Annual  Report  on  the  Highways  of  Maryland  contains,  on  pages 
118  to  120,  the  results  of  one  hundred  and  twenty  N.  B.  M.  A. 
rattler  tests  on  paving  bricks,  some  of  the  samples  having  been 
selected  by  the  City  Engineer  of  Baltimore  and  some  by  the  man- 
ufacturers. The  results  by  localities  are  as  follows,  in  the  order 
of  the  quality  of  the  bricks:  Eleven  lots  from  Ohio  gave  a  mean 
loss  of  18.2  per  cent  with  a  range  from  16.2  to  20.0;  ten  lots  from 
West  Virginia  had  a  mean  loss  of  22.7  per  cent  and  a  range  from 
17.0  to  35;  twenty-four  lots  from  Pennsylvania  showed  a  mean 
loss  of  26.8  per  cent  and  a  range  from  18.6  to  55.8,  and  omitting 


AKT.   l.j  THE   BRICK.  48? 

two  lots  the  average  is  24.8  per  cent  and  the  range  from  18.6  to 
34.2;  and  nine  lots  from  Maryland  gave  an  average  loss  of  32.1 
per  cent  with  a  range  from  25.3  to  48.7,  and  omitting  one  result 
the  mean  is  26.3  per  cent  and  the  range  from  25.3  to  37.6. 

748.  All  of  the  above  data  are  for  blocks  approximately  3" 
X  4"  X  9".  Bricks  approximately  2"  X  4"  X  8"  will  lose  from 
2  to  6  per  cent  more  than  the  above  blocks;  but  not  enough  data 
have  been  accumulated  to  determine  with  any  accuracy  the 
effect  of  size  upon  the  loss  in  the  rattler  test.*  It  is  difficult  to 
secure  the  specimens  necessary  in  making  the  comparison. 

749.  A  study  of  the  details  of  the  experiments  referred  to 
above,  indicates  that  an  occasional  manufacturer  can  furnish  pav- 
ing blocks  giving  a  loss  of  15  per  cent  or  even  less;  but  whether  it 
is  wise  so  to  specify  will  depend  upon  the  service  required  and 
upon  the  cost  of  different  grades  of  paving  blocks.  A  severe 
specification  will  require  more  careful  culling  of  the  product  of  the 
kiln  and  will  also  limit  competition, — both  of  which  demands  will 
increase  the  cost.  The  limit  to  be  specified  in  any  particular  case 
will  depend  upon  the  special  conditions. 

750.  The  N.  B.  M.  A.  standard  rattler  test  is  defective  in  that 
it  determines  only  the  average  loss  of  two  charges  of  brick  and 
gives  no  information  as  to  the  uniformity  of  the  quality  of  the 
individual  bricks.  Uniformity  of  wear  is  nearly  as  important  as 
durability,  for  a  single  soft  brick  soon  causes  a  hole,  and  the  blows 
of  the  wheels  in  dropping  into  this  hole  soon  destroy  the  adjacent 
pavement,  however  good  the  brick  are.  The  value  of  the  test 
would  be  materially  increased,  if  in  specifying  the  limit  for  the 
average  loss  in  the  rattler  a  statement  were  also  made  of  the 
amount  that  the  loss  of  one  charge  may  be  permitted  to  go  above 
or  below  the  average  of  two.  A  study  of  the  tests  described  in 
the  preceding  section  shows  that  loss  of  each  charge  should  not 
vary  from  the  mean  of  the  two  by  more  than  10  or  12  per  cent  of 
that  result.  This  modification  would  add  nothing  to  the  cost  of 
the  test  or  to  the  time  required  in  making  it. 

The  value  of  the  test  could  be  further  increased  by  determin- 

*  For  a  few  data  on  the  relative  losses  of  different  sizes  when  tested  by  \h°> 
former  N.  B.  M.  A.  standard,  see  Report  of  Paving  Brick  Commission,  p.  56. 


488  BRICK  PAVEMENTS.  [CHAP.  XIV. 

ing  the  loss  of  each  individual  brick,  and  specifying  a  limit  to  the 
variation  of  any  brick  from  the  average  of  the  charge.  Exper- 
iments show  that  with  the  best  paving  blocks  the  loss  of  any  indi- 
vidual brick  will  differ  25  to  30  per  cent  of  the  mean  of  the  charge 
from  that  result.  Part  of  this  variation  is  due  doubtless  to  acci- 
dental differences  in  making  the  tests,  but  a  large  part  of  it  is  due 
to  lack  of  uniformity  of  the  bricks  themselves. 

To  determine  the  losses  of  the  individual  blocks  will  require 
the  marking  of  the  blocks  so  that  they  may  be  identified  after  the 
test  is  completed.  One  way  of  accomplishing  this  result  is  to  drill 
holes,  say,  \  inch  in  diameter,  in  the  side  of  the  block;  and  another 
is  to  mark  the  brick  with  a  cold  chisel,  in  which  case  they  must 
be  examined  at  intervals  during  the  test  and  be  re-marked  as 
the  original  marks  wear  off. 

751.  Talbot-Jones  Method.  In  February,  1899,  Mr.  Gomer 
Jones,  City  Engineer  of  Geneva,  N.  Y.,  read  a  paper  before  the 
National  Brick  Manufacturers'  Association  advocating  a  method 
of  testing  paving  brick  by  clamping  them  in  pockets  on  the  inside 
of  the  staves  of  a  rattler,  and  inserting  into  this  chamber  a  charge 
of  lj-inch  cast-iron  cubes.  It  was  claimed  that  this  method  of 
testing  more  nearly  represented  the  condition  of  service  in  the 
pavement  than  either  of  those  described  above.  The  investigation 
of  this  method  was  referred  to  the  Association's  Committee  on 
Technical  Investigation,  which  called  to  its  aid  a  Board  of  Expert 
Engineers  and  conducted  a  series  of  experiments  with  a  modifica- 
tion of  the  Jones  rattler,  or  rather  a  substitute  for  it,  proposed 
in  1900  by  Prof.  A.  X.  Talbot,  and  named  by  the  Committee  the 
Talbot-Jones  rattler. 

The  Talbot-Jones  rattler  consists  of  a  short  over-hung  cylinder 
in  which  the  bricks  are  clamped  by  bolts  between  them  and  bearing 
on  their  ends.  The  bricks  are  so  placed  as  to  form  a  lining  to  the 
cylinder  in  which  the  cast-iron  cubes  are  placed.  Fig.  127  is  a  view  of 
the  rattling  chamber  with  one  end  removed,  before  the  bricks 
have  been  tested;  and  Fig.  128  the  same  after  the  bricks  have  been 
tested.  Fig.  129,  page  490,  shows  the  details  of  construction  of  the 
rattler.  A  short  sheet-steel  cylinder  is  fastened  to  a  cast-iron  face- 
plate by  bent  steel  bars.  The  end  of  the  cylinder  lacks  about  |-inch 
of  being  in  contact  with  the  face-plate,  the  space  being  left  for  the 


AKT.  1.] 


THE   BRICK. 


489 


F10.  127.— Talbot-Jones  Rattler  before  Running. 


Fig.  128.— Talbot-Jones  Rattler  after  Running. 


490 


BRICK    PAVEMENT? 


[CHAP.   XIV. 


escape  of  dust  and  chips.  About  1£  inches  from  the  circumference 
of  the  face-plate  is  a  T-shaped  groove  opening  to  the  front  in  which 
are  pli^ed  the  heads  of  the  bolts  that  clamp  the  bricks  in  position. 


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Fig.  129. — Details  of  Construction  of  Talbot- Jones  Rattler. 


Access  to  this  groove  is  had  through  six  lj-inch  holes  in  the  back 
of  the  face-plate.  About  3§  inches  from  its  circumference,  the 
front  of  the  face-plate  is  recessed  about  f-inch.     The  lower  part  of 


AKT.   1.]  THE   BRICK.  491 

the  back  end  of  the  brick  is  in  contact  with  the  face-plate;  but, 
owing  to  the  recess  described  above,  the  inner  edge  of  the  back 
end  of  the  brick  is  unsupported,  an  arrangement  which  allows  the 
impact  of  the  iron  cubes  to  have  their  full  effect.  Strips  of  wood 
are  placed  between  the  outer  edges  of  the  bricks  to  keep  them  the 
right  distance  apart  and  to  aid  in  keeping  them  in  position.  After 
the  bricks  are  in  place,  the  free  end  of  the  cylinder  is  closed  with 
a  wood  disk,  which  is  fastened  in  place  by  the  four  long  bolts  shown 
in  Fig.  128  and  129.  In  the  center  of  the  large  wood  disk  is  a  small 
opening  for  inserting  the  cast-iron  cubes  and  for  viewing  the  pro- 
gress of  the  experiment. 

752.  This  machine  is  still  in  the  experimental  stage,  having 
been  used  only  by  Prof.  Edward  Orton,  Jr.,  of  Ohio  State  Uni- 
versity, in  some  tests  made  for  the  Technical  Committee  of  the 
National  Brick  Manufacturers'  Association,  and  by  Messrs.  John 
Barr  and  C.  W.  Malcolm,  Civil  Engineering  students,  University 
of  Illinois,  in  thesis  work ;  *  and  consequently  the  best  relations 
have  not  been  determined. 

Professor  Orton  used  60  pounds  of  2|-inch  cast-iron  cubes  and 
90  pounds  of  l^-inch  cubes,  and  ran  the  machine  at  41  revolutions 
per  minute  for  3,000  revolutions.  As  a  result  of  a  series  of  experi- 
ments with  different  spaces  between  the  brick,  he  recommended 
a  space  of  1  inch.  Messrs.  Barr  and  Malcolm  used  1^-inch  cast- 
iron  cubes.  They  used  the  same  composition  of  abrasive  material 
and  ran  the  machine  at  the  same  speed  as  Professor  Orton,  but 
used  -Hnch  spacing. 

The  size  of  the  cubes  determines  the  relative  intensity  of  the 
impact  and  abrasion ;  and  the  size  of  the  crack  between  the  blocks, 
together  with  the  speed,  governs  the  height  to  which  the  abrading 
material  is  carried,  and  consequently  has  a  marked  influence  upon 
the  amount  the  blocks  lose. 

753.  Professor  Orton  found  the  average  loss  of  six  different 
kinds  of  paving  blocks  to  be  15.3  per  cent  by  the  N.  B.  M.  A.  stan- 
dard test,  and  12.8  per  cent  by  the  Talbot- Jones  process  as  above. 

Messrs.  Barr  and  Malcolm  found  the  average  loss  of  two  kinds 

*  Bachelor's  Theses,  University  of  Illinois  Library,  1902. 


492  BRICK    PAVEMENTS.  [CHAP.   XIV. 

of  paving  blocks  by  the  N.  B.  M.  A.  standard  test  to  be  21.2  per 
cent  and  by  the  Talbot- Jones  process  as  above  to  be  5.1  per  cent; 
and  with  bricks  2J"  X  4"  X  8f"  they  found  the  loss  by  the  N.  B. 
M.  A.  standard  test  to  be  24.2  per  cent,  and  by  the  Talbot- Jones 
process  9.4  per  cent. 

754.  The  essential  difference  between  this  process  and  the  pre- 
ceding one  is  that  in  this  only  one  surface  of  the  brick  is  exposed 
to  action,  while  in  the  preceding  method  all  sides  are  subjected  to 
wear.  Many  believe  that  the  Talbot-Jones  test  more  nearly  approx- 
imates the  conditions  in  the  pavement  than  the  N.  B.  M.  A.  stan- 
dard ;  but  owing  to  the  absence  of  any  lateral  support  of  the 
brick  in  the  Talbot-Jones  rattler,  the  former  does  not  very  closely 
represent  the  conditions  in  the  pavement.  However,  the  wear,  for 
some  grades  of  brick  at  least,  is  strikingly  similar  to  that  in  the 
pavement.  The  Talbot- Jones  method  gives  a  considerably  wider 
range  between  good  and  poor  brick  than  does  the  N.  B.  M.  A.standard. 

The  time  required  by  the  Talbot-Jones  process  is  twice  that  re- 
quired by  the  standard  process  for  one  charge;  but  to  obtain  the 
average  result  required  by  the  latter  method,  a  time  equal  to  one 
test  with  the  former  machine  is  required.  The  number  of  brick 
treated  in  one  test  with  the  Talbot-Jones  machine  is  substantially 
the  same  as  in  two  tests  by  the  N.  B.  M.  A.  standard.  The  power 
consumed  in  revolving  the  rattler  and  its  charge  is  a  little  less  in 
the  Talbot- Jones  than  in  the  standard  process.  It  is  easier  to  deter- 
mine the  losses  of  individual  bricks  with  the  Taibot-Jones  form 
than  with  the  standard  rattler.  The  skill  required  in  conducting 
the  test  by  the  Talbot-Jones  process  is  distinctly  more  than  for  the 
N.  B.  M.  A.  standard,  as  the  preparation  of  a  charge  for  rattling 
requires  much  more  care  and  discretion;  and  the  supplies  con- 
sumed are  more  expensive,  as  there  are  many  more  bolts  under 
continual  wear  and  many  more  small  accessories  to  provide,  such 
as  wedges,  gaskets,  washers,  clips,  etc.  The  iron  abrasives  worn 
out  are  less  expensive  than  those  of  the  standard  process.  The 
first  cost  of  the  Talbot-Jones  machine  is  greater  and  the  workman- 
ship is  distinctly  of  a  better  grade  than  is  required  for  the  stand- 
ard process.  The  cost  of  a  test  by  the  Talbot-Jones  process,  how- 
ever, is  somewhat  greater  in  money,  time,  energy,  and  skill  than 
the  N.  B.  M.  A.  standard. 


ART.    1.]  THE    BRICK.  493 

755.  The  rattler  test  should  be  regarded  as  a  means  (1)  of 
determining  whether  any  particular  brand  of  brick  meets  the 
specifications  and  (2)  of  comparing  any  new  brick  with  those  that 
have  been  tested  by  service  in  the  pavement ;  but  (3)  it  should  not 
be  used  to  discriminate  between  two  grades  of  brick  differing  only 
slightly  in  rattler  losses,  since  owing  to  variations  in  the  quality  of 
different  brick  from  the  same  lot  and  to  accidental  variations  in 
making  the  test,  the  rattler  can  not  give  mathematical  accuracy. 
Further,  the  loss  in  the  rattler  is  the  combined  loss  due  to  impact 
and  abrasion,  and  consequently  the  loss  of  a  brittle  brick  may  be 
chiefly  due  to  chipping,  while  that  of  a  soft  tough  brick  may  be  due 
principally  to  abrasion.  It  is  not  known  that  the  relative  losses  due 
to  impact  and  abrasion  in  the  rattler  is  the  same  as  in  the  pave- 
ment ;  and  hence  for  this  reason  also  the  rattler  should  not  be 
used  to  discriminate  between  two  grades  of  high-quality  paving 
brick. 

756.  Service  Tests.  Three  experiments  are  in  progress  to 
determine  the  relative  qualities  of  paving  blocks  by  actual  service 
in  the  pavement.  Each  experiment  consists  in  testing  a  number 
of  standard  grades  of  paving  blocks  and  then  laying  short  sections 
of  pavement  with  each  of  the  several  kinds. 

The  first  of  these  experimental  sections  was  laid  in  May,  1898, 
in  Detroit,  Mich.,  on  Franklin  Street,  between  Beallbien  Street  and 
the  Grand  Trunk  freight  depot.  Transverse  strips  of  fourteen  kinds 
of  brick  were  laid  in  a  distance  of  222  feet.  The  blocks  were  tested 
by  the  former  N.  B.  M.  A.  standard  rattler  test  (§  742).  The 
foundation  was  6  inches  of  concrete.  The  sand  cushion  was  1 
inch  thick,  and  the  joints  were  filled  with  coal-tar  distillate  No.  6. 
For  a  comparison  between  the  results  of  the  rattler  tests  and  a 
general  observation  of  the  effect  of  three  years'  wear  in  the  pave-, 
ment,  see  Municipal  Engineering,  Vol.  22,  pages  283-84,  and  363- 
65.  These  comparisons  fail  to  show  any  close  agreement  be- 
tween the  former  N.  B.  M.  A.  rattler  test  and  service  in  the  pavement. 

The  second  experiment  was  inaugurated  Oct.  16,  1900,  on  the 
driveway  leading  to  the  Chicago  Avenue  pumping  station  at 
Chicago,  111.  Nine  kinds  of  paving  blocks  w^ere  laid  in  a  distance 
of  392  feet.  The  time  is  too  short  and  the  traffic  too  light  to  have 
yet  determined  any  valuable  results. 


494  BRICK    PAVEMENTS.  [CHAP.   XIV. 

The  third  experiment  was  begun  Nov.  2, 1901 ,  on  Holiday  Street 
between  Fayette  and  Baltimore  Street,  in  Baltimore,  Md.  Seven 
kinds  of  clay  blocks,  two  kinds  of  artificial  sheet  asphalt,  one  piece 
of  natural  rock  asphalt,  and  one  sample  of  creosoted  pine  blocks, 
were  laid  in  a  distance  of  221  feet,  the  abutting  street  at  each  end 
being  paved  with  Belgian  blocks  (§  808).  For  details  concern- 
ing the  tests  of  the  brick  and  the  construction  of  the  pavement, 
see  Annual  Report  of  the  City  Engineer  of  Baltimore  for  1901, 
pages  73-74  and  112.  The  bricks  were  tested  by  the  N.  B.  M.  A. 
standard  rattler  test,  and  were  laid  on  a  lj-inch  sand  cushion 
resting  on  new  cobble-stone  pavement.  The  joints  were  filled  with 
sand.  After  eight  months'  wear,  the  fourth  best  brick  block  by  the 
rattler  test  seems  to  have  worn  best  in  the  pavement,  and  the  best 
brick  block  in  the  rattler  test  seems  to  be  among  the  poorest 
in  the  pavement. 

The  non-agreement  between  the  results  of  the  rattler  test  and 
service  in  the  pavement  indicates  that  the  rattler  test  is  not  an 
infallible  guide  in  selecting  paving  brick;  but  this  disagreement 
does  not  prove  that  this  test  should  be  abandoned.  The  rattler 
test  is  the  best  method  known  for  determining  the  qualities*  of 
paving  brick,  and  possibly  it  may  be  ultimately  modified  so  as 
more  closely  to  agree  with  results  of  actual  service. 

Art.  2.     Construction. 

757.  Thus  far,  in  the  history  of  brick  pavements,  attention  has 
been  centered  in  the  quality  of  the  brick,  while  comparatively 
little  attention  has  been  given  to  the  details  of  the  construction. 
A  good  pavement  requires  both  good  material  and  good  con- 
struction. 

758.  FOUNDATION.  Each  brick  should  have  an  adequate  sup- 
port from  below,  as  otherwise  the  loaded  wheels  will  force  it  down- 
ward and  make  the  surface  uneven,  a  condition  which  conduces  to 
the  rapid  destruction  of  the  pavement  by  the  impact  of  the  wheels 
in  passing  over  the  depressions.  There  are  several  forms  of  foun- 
dation in  common  use  for  brick  pavements. 

The  best  foundation  is  doubtless  a  bed  of  concrete  laid  as 
described    in    Art.    2,    Chapter    XII,    pages   367-82.      Fig.    130 


ART.  2.] 


CONSTRUCTION. 


495 


is  a  section  of  a  brick  pavement  having  a  concrete  foundation. 
In  recent  years  there  has  been  a  marked  tendency  to  use  concrete 
for  the  foundation  of  a  brick  pavement;  although  a  brick  pave- 
ment should  have  adequate  support,  and  although  concrete  when 
properly  made  makes  an  excellent  foundation,  it  does  not  follow 
that  every  such  pavement  should  be  laid  upon  concrete, — at  least 
upon  a  6-inch  layer,  as  is  the  common  practice.  Under  certain 
conditions  a  layer  of  macadam  may  be  cheaper  and  equally  effec- 
tive— see  §  562,  Art.  3,  Chapter  XII ;  and  sometimes  a  layer  of 


Fig.  130.— Section  of  Brick  Pavement  with  Concrete  Foundation. 


gravel  of  proper  thickness,  when  laid  as  described  in  §  564,  Art.  3, 
Chapter  XII,  is  sufficient.  In  some  localities  the  natural  soil  is  so 
gravelly  that  it  needs  only  to  be  leveled  and  rolled  to  make  a  rea- 
sonably good  foundation,  particularly  if  the  traffic  is  only  mod- 
erately heavy.  Many  cities,  some  of  which  have  a  considerable 
traffic,  for  example,  Cleveland,  Ohio,  and  Galesburg,  Illinois,  thus 
lay  brick  directly  upon  the  native  soil.  Under  certain  condi- 
tions 4-inch  macadam  roads  have  given  fair  service  (see  §  321),  and 
a  4-inch  course  of  brick  has  at  least  approximately  as  much  sta- 
bility as  an  equal  thickness  of  broken  stone. 

However,  it  is  poor  policy  to  build  an  inadequate  foundation 


496 


BRICK    PAVEMENTS. 


[CHAP.    XIV. 


for  a  brick  pavement.  The  foundation  for  any  block  pavement, 
whether  of  brick,  stone,  or  wood,  should  be  substantial  enough  to 
keep  the  blocks  in  position  so  that  the  traffic  will  be  received  per- 
pendicular to  the  face  of  the  block,  since  then  the  surface  of  the  pave- 
ment will  be  smoother  and  the  wear  upon  the  blocks  will  be  less. 
Brick  pavements,  being  made  of  comparatively  small  blocks,  are 
proportionally  more  injured  by  any  derangement  of  the  blocks, 
and  consequently  require  a  very  carefully  constructed  foundation. 
The  best  foundation  for  any  particular  work  will  depend  upon  the 
character  of  the  soil  and  the  availability  of  the  various  materials. 
759.  During  the  first  ten  or  fifteen  years  after  the  introduction 


Fig.  131.— Section  op  Brick  Pavement  with  Brick  Foundation. 


of  brick  pavements  in  the  Middle  West,  the  foundation  consisted 
almost  exclusively  of  a  course  of  brick  laid  flatwise  on  a  thin  bed 
of  gravel  or  cinders.  Fig.  131  is  a  section  of  a  brick  pavement 
having  a  brick  foundation.  Such  pavements  are  generally  known 
as  two-course  brick  pavements.  The  layer  of  cinders  or  gravel 
was  leveled,  and  inferior  paving  brick  were  laid  flatwise  thereon; 
and  then  the  joints  of  the  bricks  were  swept  full  of  sand.  Brick 
foundations  were  formerly  used  very  extensively,  but  recently  have 
generally  given  place  either  to  concrete,  crushed  stone,  or  gravel, 
and  are  used  now  only  in  a  few  localities  which  are  remote 
from    stone     quarries    and     gravel     pits    in    which    brick    are 


ART.    2.]  CONSTRUCTION.  497 


comparatively  cheap.  The  chief  defect  in  this  form  of  founda- 
tion was  that  the  joints  of  the  lower  course  were  not  fully  filled, 
and  consequently  after  the  pavement  was  in  service  the  sand  of 
the  cushion  coat  (the  layer  between  the  two  courses  of  brick) 
would  work  into  these  joints  and  permit  the  bricks  in  the  wearing 
course  to  settle.  To  cheapen  the  pavement,  broken  and  chipped 
brick  were  used  in  the  lower  course,  and  the  tendency  was  to 
place  the  larger  face  uppermost,  thus  making  it  nearly  impossible 
to  fill  entirely  the  joints  during  the  time  of  construction.  This 
form  of  foundation  was  abandoned  on  account  of  its  cost  and  in- 
ferior quality. 

760.  The  first  brick  pavement  in  this  country,  that  at  Charles- 
ton, W.  Va.,  was  laid  on  a  foundation  of  1-inch  tarred  boards  resting 
on  a  layer  of  3  or  4  inches  of  sand,  with  a  cushion  of  coat  of  1£  inches 
of  sand  between  the  bricks  and  the  boards.  This  form,  known  as 
the  Hale  or  the  Charleston  foundation,  was  not  used  to  any  consid- 
erable extent,  and  has  been  entirely  abandoned. 

761.  CUSHION  LAYER.  This  is  a  layer  of  sand  between  the  foun- 
dation and  the  wearing  course  of  brick,  to  secure  a  uniform  bearing 
for  the  latter.  The  proper  thickness  of  this  layer  will  depend  upon 
the  regularity  of  the  upper  surface  of  the  concrete  foundation  and 
also  upon  the  uniformity  of  the  size  of  the  bricks.  It  should  be 
thick  enough  to  give  a  uniform  support  to  the  bricks,  and  any  greater 
thickness  does  no  particular  harm  except  that  it  is  a  little  more 
difficult  to  spread  exactly  uniformly  a  thick  layer  than  a  thin  one. 
In  common  practice,  the  thickness  varies  from  h  to  2\  inches,  but 
usually  from  1  to  2  inches.  A  thickness  of  1-inch  is  enough  to  fill 
up  all  reasonable  irregularities  of  the  foundation,  but  it  is  not 
enough  to  permit  a  uniform  bedding  of  the  brick  by  rolling.  Ap- 
parently a  1-inch  cushion  is  not  thick  enough  to  permit  the  sand 
to  flow  sufficiently  to  adjust  itself  to  the  inequalities  of  the  brick. 
Unless  the  blocks  are  unusually  uniform,  the  cushion  layer  should 
be  2  inches  thick. 

The  thickness  should  be  as  uniform  as  possible,  so  that  the 
bricks  will  settle  evenly  during  the  rolling;  and  therefore  the  top 
of  the  concrete  foundation  should  be  carefully  finished  with  a 
surface  parallel  to  the  surface  of  the  pavement.  Not  infrequently 
loose  fragments  of  stone  are  left  on  the  surface  of  the  concrete, 


498  BRICK    PAVEMENTS.  [CHAP.   XIV. 

a  result  which  is  very  undesirable,  since  they  necessitate  a  thicker 
cushion  and  at  best  prevent  the  bricks  from  coming  to  a  uniform 
bearing.  With  good  workmanship  in  laying  the  concrete,  there 
will  be  no  loose  pieces  of  stone  on  the  surface  ;  and  if  they  do 
happen  to  get  there,  they  should  be  removed  before  laying  the 
cushion  coat. 

In  adjusting  the  thickness  of  the  sand  cushion  adjoining  a 
concrete  gutter,  care  should  be  taken  that  the  upper  surface 
of  the  brick  after  being  rolled  is  not  below  the  upper  edge  of  the 
gutter. 

762.  When  the  sand  cushion  is  laid  on  a  foundation  of  broken 
stone  (§  562),  care  must  be  taken  to  roll  the  stone  so  that  the  jar 
of  the  traffic  will  not  cause  the  sand  to  wrork  into  the  broken  stone, 
thus  permitting  the  pavement  to  settle  and  to  become  rough  and 
uneven.  If  the  broken  stone  is  rolled  until  the  surface  of  the  layer 
is  firm  and  solid  and  does  not  shake  under  the  foot  in  walking  over 
it,  unless  the  stone  is  very  hard  and  tough  there  is  not  much  danger 
of  the  sand  sifting  into  the  stone. 

763.  The  sand  for  the  cushion  should  preferably  be  so  fine  as  to 
be  of  a  soft,  velvety  nature,  and  should  contain  no  pebbles  of  any 
considerable  size,  or  loam,  or  vegetable  matter.  The  size  of 
pebbles  permissible  depends  upon  the  thickness  of  the  sand  bed. 
Pebbles  will  prevent  the.  brick  from  having  a  uniform  bearing;  the 
loam  is  likely  to  be  washed  to  the  bottom  of  the  layer  and  cause  the 
brick  to  settle;  while  the  vegetable  matter  will  decay  or  wash 
away,  and  leave  the  brick  unsupported.  The  sand  should  be  dry 
when  it  is  spread.  Even  a  small  per  cent  of  moisture  in  the  sand 
adds  considerably  to  its  volume,  particularly  if  it  is  fine  ;  and 
hence  if  the  sand  when  laid  is  wet  and  dry  in  spots,  the  cushion 
will  not  be  of  uniform  thickness  when  dry.  The  shrinkage  of 
the  sand  cushion  away  from  the  brick,  under  certain  conditions 
causes  an  unpleasant  rumbling  of  the  pavement  when  heavy  vehi- 
cles pass  over  it  (see  §  781). 

764.  The  spreading  of  the  sand  should  be  carefully  done,  so  as 
to  secure  a  uniform  thickness  and  to  have  its  upper  surface  exactly 
parallel  to  the  top  of  the  finished  pavement.  After  the  sand  has 
been  distributed  approximately  to  the  proper  thickness  with  a 
shovel,  the  surface  should  be  leveled  by  drawing  over  it  a  tern- 


ART.   2.]  CONSTRUCTION.  49$ 

plate  conforming  exactly  to  the  curvature  of  the  cross  section  of 
the  proposed  surface  of  the  pavement.  Practice  differs  consid- 
erably as  to  the  length  of  the  template. 

Some  contractors  make  the  template  the  full  width  of  the 
pavement,  if  that  is  less  than  about  30  feet,  and  for  a  wider  pave- 
ment make  the  template  half  the  width  of  the  street.  This  form 
of  template  must  be  made  of  a  2-inch  pine  plank  of  sufficient 
width  to  permit  of  the  cutting  of  its  lower  edge  to  the  proper  curva- 
ture, which  may  be  determined  by  the  method  explained  in  §  310 
(page  200).  If  the  template  is  long,  it  must  be  braced  to  prevent 
bending  and  sagging;  and  it  must  have  a  long  and  substantial 
handle  at  each  end  by  which  to  draw  it  forward,  and  another  handle 
at  each  end  by  which  to  carry  it  backward.  It  is  desirable  that 
the  template  shall  have  considerable  weight  to  keep  it  from  lifting 
up  as  it  is  drawn  forward;  and  when  being  drawn  forward,  the 
face  of  it  should  lean  backward  a  little  to  keep  it  from  lifting  up. 
At  each  end  there  should  be  a  roller  or  a  metal  runner  to  carry  the 
template  along  the  top  of  the  curb  or  along  the  edge  of  the  con- 
crete gutter.  If  it  is  to  run  on  top  of  the  curb,  a  roller  also  should 
be  provided  to  keep  it  away  from  the  curb.  If  the  length  of  the 
template  is  equal  to  half  the  width  of  the  street,  one  end  of  it  may 
run  upon  a  screed,  or  wood  strip,  equal  in  thickness  to  that  of  the 
cushion  layer,  placed  in  the  center  of  the  street.  If  there  is  a  car 
track  in  the  street,  one  end  of  the  template  may  be  made  to  run 
on  the  rail. 

A  long  template  requires  considerable  force  to  draw  it  forward, 
some  contractors  using  one  or  two  horses  for  this  purpose,  and  it 
is  difficult  to  move  backward.  Other  contractors,  therefore,  use 
a  template  equal  to  one  quarter  of  the  width  of  the  pavement. 
For  a  pavement  30  to  40  feet  wide,  screeds  made  of  2-inch  by  4- inch 
scantlings  are  placed  at  the  crown,  in  the  gutters,  and  also  midway 
between  the  crown  and  the  gutter,  being  bedded  on  a  thin  layer 
of  sand  so  that  their  tops  conform  to  the  finished  surface  of  the 
proposed  sand  cushion.  The  position  of  these  screeds  is  deter- 
mined by  measuring  down  from  a  string  stretched  from  curb  to 
curb.  The  template  may  be  made  of  a  1-inch  by  6-inch  plank, 
with  a  1-inch  by  2-inch  handle  braced  by  two  1-inch  by  2-inch 
pieces.     The  edge  should  be  hollowed  out  to  fit  the  curved  surface- 


500  BRICK  PAVEMENTS.  [CHAP.  XIV. 

of  the  pavement,  although  often  this  is  not  done.      The  middle 

ordinate  for  the  curved  cutting  edge  of  the  template  may  be  com- 

C  (P 
puted  by  the  formula  m  =  ~j^,  in  which  m  is  the  middle  ordinate 

in  inches,  C  the  crown  of  the  pavement  in  inches,  d  half  the  length 
of  the  template  in  feet  and  D  half  the  width  of  the  pavement  in  feet. 
After  the  sand  for  the  cushion  layer  has  been  distributed  with 
shovels,  the  template  should  be  drawn  slowly  over  it  several  times, 
any  depressions  that  develop  being  filled  by  sprinkling  sand  into 
them  with  a  shovel.  A  considerable  quantity  of  sand  should  be 
drawn  along  in  front  of  the  template,  as  this  aids  materially  in 
packing  the  bed.  It  is  necessary  to  draw  the  template  several 
times  to  pack  the  sand  well,  particularly  if  there  are  wet  and  dry 
spots,  as  the  successive  jarring  of  the  sand  grains  causes  them  to 
settle  more  closely  together.  When  the  sand  cushion  is  properly 
packed  it  will  have  a  uniform,  smooth,  velvety  appearance,  and  will 
not  look  rough,  porous,  and  grainy. 

765.  The  surface  of  the  cushion  layer  is  often  prepared  with  a 
short  lute  or  scraper  without  any  screeds;  but  the  template  and 
screeds  secure  a  more  uniform  surface  and  also  give  a  groater 
compression  and  a  more  even  bed.  With  hand  luting  the  surface 
of  the  pavement  is  almost  certain  to  be  covered  with  saucer-like 
depressions  after  it  has  been  rolled.  Hand  luting  should  be  pro- 
hibited except  where  the  use  of  the  template  is  impossible,  as 
around  man-hole  covers,  at  street  intersections,  etc. 

A  considerable  part  of  the  difference  in  tractive  resistance 
between  brick  pavements  No.  4.  and  Nos.  5  and  6  of  Table  8,  page 
29,  is  due  chiefly  to  the  difference  in  the  preparation  of  the  sand 
cushion,  the  remainder  of  the  difference  being  in  the  rolling  of  the 
brick  (§  771). 

766.  LAYING  THE  BRICK.  Delivery.  Some  contractors  pile 
the  brick  at  the  side  of  the  street  before  commencing  the  grading, 
while  others  haul  them  to  the  street  and  take  them  directly  to  the 
men  who  lay  them.  If  the  brick  can  be  had  at  the  kiln  and  are 
shipped  exactly  when  desired,  there  is  a  possibility  of  saving  24  to 
3  cents  per  square  yard  by  the  last  method;  but  there  is  danger 
of  the  street's  being  kept  closed  needlessly  long  owing  either  to 
bad  wagon  roads  or  to  a  failure  in  railroad  transportation.     The 


ART.  2.]  CONSTRUCTION".  501 

bricks  are  hauled  over  those  just  placed,  planks  being  laid  down 
to  protect  the  brick ;  but  considerable  damage  is  caused  in  turning 
the  empty  wagons,  since  the  bricks  are  settled  unevenly. 

Most  contractors  use  wheel-barrows  to  deliver  the  brick  to  the 
men  who  lay  them,  but  a  few  carry  them  on  a  board  about  6  inches 
wide  and  24  inches  long.  The  advantages  claimed  for  the  last 
method  are  that  it  is  cheaper,  chips  the  brick  less,  and  delivers 
the  brick  convenient  to  the  setters.  The  first  claim  is  doubtful, 
at  least  with  intelligent  and  efficient  laborers;  and  there  is  but  little 
danger  of  chipping  good  paving  brick.  When  the  brick  are  carried 
on  a  board  they  are  delivered  convenient  to  the  setters,  and  there 
is  less  likelihood  of  disturbing  the  position  of  the  bricks  already  set; 
but  this  method  is  too  expensive  to  justify  its  use.  The  wheel- 
barrows should  never  be  run  on  the  bare  bricks  just  laid,  since  it 
settles  them  unevenly,  but  planks  should  be  laid  down  upon  which 
to  run  the  wheel -barrows.  In  dumping  the  barrows,  they  should  be 
turned  to  face  up  or  down  the  street,  and  then  be  tipped  until  the 
brick  slide  gently  out  toward  the  curb,  as  otherwise  there  is  a  con- 
tinuous widening  of  the  joints  between  the  courses  and  a  disturb- 
ance of  the  alignment  of  the  rows. 

767.  Direction  of  Courses.  It  is  customary  to  lay  the  brick 
with  the  length  perpendicular  to  the  curb,  except  at  street  intersec- 
tions ;  but  there  are  a  few  cities  in  which  the  brick  are  laid  in  courses 
making  an  angle  of  45  degrees  with  the  length  of  the  street,  with 
the  idea  that  the  tendency  to  form  ruts  would  be  less  if  the  wheels 
crossed  the  bricks  diagonally.  There  is  no  advantage  in  the  diag- 
onal over  the  square  courses ;  they  are  more  difficult  to  lay,  cutting 
the  corner  of  the  brick  in  making  the  fit  next  to  the  curb  is  waste- 
ful of  material,  and  the  diagonal  courses  do  not  give  as  good  foot- 
hold to  the  horses.  Occasionally  a  few  courses  of  brick  are  laid 
longitudinally  in  the  gutter,  similar  to  the  practice  with  stone 
blocks ;  but  this  is  unnecessary,  since  the  brick  pavement  is  much 
smoother  than  the  ordinary  stone-block  pavement,  and  besides 
the  running  joint  where  the  transverse  and  the  longitudinal  sec- 
tions join  is  likely  to  develop  into  a  rut. 

768.  At  street  intersections  and  junctions  the  bricks  should  be 
laid  diagonally — a  compromise  position  between  the  directions  of 
the  travel  on  the  two  streets.     Street  intersections  need  special 


502  BRICK    PAVEMENTS.  [CHAP.   XIV. 

care  in  construction,  since  they  are  exposed  to  the  traffic  of  two 
streets.  Fig.  132  shows  the  usual  arrangement  of  the  courses  for 
a  street  intersection;  and  Fig.  133  and  Fig.  134  (page  504)  show 
two  other  arrangements  that  have  occasionally  been  used.  Slight 
objections  have  been  urged  against  all  three  plans.  The  bond 
in  Fig.  132  is  weak  along  the  middle  line  of  each  street;  Fig.  133 


Fig.  132.— Double-diagonal  Brick  Intersection. 

is  objectionable  owing  to  the  tendency  of  ruts  to  form  along  the 
lines  running  through  the  ends  of  the  bricks;  and  Fig.  134  is 
defective  since  traffic  around  the  corners  A  and  B  is  parallel  to  the 
courses  of  brick. 

At  a  street  junction  only  half  of  the  common  area  should  be 
laid  with  diagonal  courses.  For  example,  assuming  that  in  Fig. 
132  the  street  enters  the  lower  side  of  the  transverse  street  but  does 
not  cross  it,  then  the  lower  half  of  the  intersection  would  be  laid 
with  courses  as  in  the  diagram,    while   in   the   upper   half  the 


ART.  2.] 


CONSTRUCTION. 


503 


length  of  the  bricks  would  be  perpendicular  to  the  transverse 
street. 

769.  Setting  the  Brick.  In  setting  the  brick  the  man  should 
stand  on  those  already  laid,  and  not  upon  the  sand  cushion.  Under 
no  consideration  should  the  sand  bed  be  disturbed.  The  brick  should 
be  set  on  edge  as  closely  and  compactly  as  possible,  each  being 
pressed  both  endwise  and  sidewise  against  those  already  laid.     The 


Fig.  133.— Herring-bone  Brick  Intersection. 


bricks  are  stronger  and  more  durable  than  any  material  that  can 
be  used  to  fill  the  joints,  and  consequently  the  thinner  the  joints 
the  better.  The  bond  should  be  approximately  a  half  brick.  If 
the  brick  were  laid  without  bond,  ruts  would  be  likely  to  form 
along  the  continuous  end-joints;  and  therefore  the  more  the 
bond  che  better.  No  bats  should  be  used,  except  in  making 
closures;  and  in  cutting  a  brick  to  close  a   course,  care  should 


504 


BRICK    PAVEMENTS. 


[CH~P.   XIV. 


be  taken  to  get  a  square  end  and  to  make  a  tight  fit.  Fig  135 
shows  the  hammer  employed  in  cutting,  or  rather  in  breaking, 
a  brick  to  close  a  course. 


Fig.  134. — Single-diagonal  Brick  Intersection. 

Some  cities  specify  that  the  brick  shall  be  gaged  to  thickness; 
but  this  is  unnecessary,  since  even  fairly  good  brick  are  practically 

uniform.  In  some,  cities  it  is  required 
that  each  five  or  six  courses  of  brick 
shall  be  driven  up  from  the  face  by 
striking  with  a  sledge  against  a  2"  X  4" 
piece  resting  against  the  last  course;  but 
this  is  unnecessary,  if  each  brick  when 
laid  is  pressed,  or  rather  struck,  against 
the  side  of  the  course  already  in  position. 
In  any  case  the  courses  should  be  straight 
across  the  street;  and  if  they  are  not- 
laid  so,  they  should  be  straightened  by 


Fig.  135. — Brick  Paver's 
Hammer. 


ART.  2.]  CONSTRUCTION.  505 

driving  up  each  five  or  six  courses  from  the  face.  Sometimes  the 
bricks  in  a  row  are  crowded  together  endwise  by  inserting  a  crow- 
bar at  the  curb ;  but  this  is  unnecessary  provided  each  brick  as  it 
is  laid  is  bumped  against  the  end  of  the  preceding  one. 

770t  Inspecting.  After  the  bricks  are  laid,  the  pavement 
should  be  inspected,  all  soft,  broken,  and  badly  misshaped  brick 
being  marked  for  removal.  To  reveal  the  soft  brick,  it  is  customary 
to  sprinkle  the  pavement  heavily  with  a  hose.  While  the  water 
is  being  applied,  the  soft  brick  will  appear  comparatively  dry; 
but  after  the  sprinkling  is  stopped,  the  soft  brick  will  appear  to 
be  the  wetter.  A  brick  having  only  a  small  piece  chipped  from 
the  corner  or  edge  may  be  turned  over.  Objectionable  brick  may 
be  marked  with  chalk,  a  cross  or  circle  indicating  a  brick  to  be 
removed  and  a  single  straight  line  one  to  be  turned.  Rejected 
brick  are  removed  with  tongs  having  broad  flat  noses  and  long  stout 
handles. 

771.  Rolling.  After  all  rejected  brick  have  been  removed 
and  the  pavement  has  been  swept,  it  is  ready  for  rolling, 
which  should  be  done  with  a  steam  roller  weighing  from  3  to  6 
tons.  A  horse  roller  is  undesirable,  since  the  horse's  feet  disturb 
the  position  of  the  loose  brick,  and  also  since  it  is  impossible  to  roll 
the  street  transversely.  The  purpose  of  the  rolling  is  to  settle  the 
bricks  uniformly  into  the  sand  bed,  and  therefore  a  steam  roller  of 
the  asphalt  type  (Fig.  65,  page  225)  is  better  than  one  of  the  stone- 
road  type  (Fig.  64,  page  224).  A  very  heavy  roller  is  undesirable, 
at  least  in  the  beginning  of  the  rolling,  since  the  first  passage  of  it 
tilts  the  brick  to  one  side  so  much  that  it  is  nearly  impossible  to 
straighten  them  up  again.  The  roller  should  not  weigh  more  than 
six  tons,  and  four  tons  is  better.  Unless  the  top  faces  of  the  bricks 
are  brought  to  a  plane,  the  pavement  will  be  rough  and  noisy,  and 
will  lack  durability.  The  bricks  should  be  firmly  settled  into  the 
sand  bed  so  that  traffic  may  not  depress  some  of  the  brick,  which 
will  make  the  pavement  rough  and  also  make  it  wear  needlessly  fast. 

The  pavement  should  first  be  rolled  longitudinally,  beginning 
at  the  crown  and  working  toward  the  gutter,  taking  care  that  each 
return  trip  of  the  roller  covers  exactly  the  same  area  as  the  preced- 
ing trip  so  that  the  second  passage  of  the  roller  may  neutralize 
any  careening  of  the  brick  due  to  the  first  passage.     Pavements 


506  BRICK   PAVEMENTS.  [CHAP.   XIV. 


that  have  been  rolled  only  once  or  always  in  one  direction,  are 
very  much  rougher  and  more  noisy  than  when  properly  rolled.  If 
a  spot  is  skipped  on  the  return  passage  of  the  roller,  it  can  be  de- 
tected by  a  casual  inspection  or  by  the  noise  of  a  passing  vehicle. 
The  first  passage  of  the  roller  should  be  made  at  a  slow  speed,  not 
faster  than  a  slow  walk,  to  prevent  undue  canting  of  the  brick. 
After  the  pavement  has  been  rolled  longitudinally,  roll  it  back  and 
forth  transversely,  or  at  least  in  both  directions  at  an  angle  of  45 
degrees  from  curb  to  curb. 

If  the  rolling  is  well  done  the  sand  cushion  will  be  pushed  up 
between  the  brick  £  to  f  of  an  inch. 

772.  A  comparatively  few  cities  specify  that  the  brick  are  to  be 
settled  into  the  sand  bed  by  ramming.  The  weight  of  the  rammer 
varies  from  40  to  90  pounds,  usually  from  75  to  90  pounds.  For 
the  form  of  rammer  ordinarily  used,  see  Fig.  138,  page  527.  The 
rammer  is  used  on  a  2-inch  oak  plank  laid  on  the  brick  parallel  to  the 
curb.  The  proper  ramming  of  a  brick  pavement  is  exceedingly 
hard  work,  and  only  a  few  men  are  strong  enough  to  do  it  even 
fairly  well. 

Ramming  does  not  tilt  the  brick;  but  it  costs  considerably 
more,  can  not  give  as  even  a  surface,  and  is  not  likely  to  be  thor- 
oughly done.  A  few  cities  specify  that  in  ramming  the  surface  is 
to  be  trued  up  with  a  straight  edge.  An  occasional  city  specifies  that 
the  brick  shall  be  first  rammed  and  then  rolled  with  a  heavy  roller. 

In  certain  places  the  roller  can  not  be  used,  as  for  example  next 
to  the  curb,  or  near  the  edge  of  a  concrete  gutter,  or  around  man- 
hole covers,  in  which  cases  the  pavement  must  be  thoroughly 
rammed. 

77?.  Filling  the  Joints.  The  joints  should  be  filled  (1)  to  keep 
the  brick  in  the  proper  position,  (2)  to  lessen  the  chipping  of  the 
edges  of  the  brick,  and  (3)  to  prevent  water  from  penetrating  to 
the  cushion  coat  and  to  the  foundation.  Three  forms  of  filler  are 
in  common  use,  viz.:  sand,  tar,  and  hydraulic  cement. 

774.  Sand  Filler.  Sand  was  the  first  filler  employed  for  brick 
pavements,  and  in  the  Middle  West  is  even  yet  almost  exclusively 
used.  The  sand  should  be  fine  and  dry,  and  be  worked  into  the 
joints  by  sweeping  it  over  the  pavement,  which  also  should  be  dry. 
A  few  cities  specify  that  the  sand  shall  be  heated  to  dry  it,  before 


.ART.   2.]  CONSTRUCTION.  507 

being  swept  into  the  joints.  Although  the  sand  is  nominally  always 
swept  into  the  joints,  it  is  usually  simply  spread  upon  the  surface 
and  left  to  be  worked  in  by  traffic,  which  is  undesirable  since  the 
joints  are  then  partially  filled  with  manure  and  street  dirt.  The 
sand  can  be  swept  into  the  joints  effectively  and  economically  with 
a  revolving  machine  sweeper.  After  the  joints  have  been  filled,  the 
surface  of  the  pavement  is  covered  with  a  layer  of  sand  \  to  %  inch 
thick,  which  is  left  on  for  a  few  weeks  after  the  street  is  thrown 
open  to  traffic,  to  secure  the  thorough  working  down  of  the  sand 
into  every  joint.  The  cost  of  sweeping  the  pavement  and  filling 
the  joints  with  sand  is  0.15  to  0.25  cent  per  square  yard,  and  the 
cost  of  a  J-inch  layer  of  sand  at  $1.08  per  cubic  yard  is  1.5  cents 
per  square  yard.  To  cover  waste  and  contingencies,  the  sand  joint- 
filler  is  usually  estimated  at  2  cents  per  square  yard. 

The  advantages  of  a  sand  filler  are:  1.  It  is  cheap,  usually 
costing  about  2  cents  per  square  yard.  2.  The  pavement  may  be 
thrown  open  to  traffic  as  soon  as  the  bricks  are  laid.  3.  The  pave- 
ment may  be  taken  up  easily  and  without  breakage  of  the  brick. 
4.  It  is  practically  water  tight,  particularly  after  being  in  service  a 
short  time.  Whenever  a  brick  pavement  having  a  sand  filler  is 
opened,  the  sides  of  the  brick  are  always  found  dry  and  clean  a 
little  distance  below  the  wearing  surface. 

The  disadvantages  of  a  sand  filler  are:  1.  It  does  not  protect  the 
«dges  of  the  brick  from  chipping.  2.  It  may  be  washed  out  on 
steep  slopes.  3.  It  is  removed  from  the  top  of  the  joints  by  the 
street  sweeper — either  the  broom  or  the  pneumatic. 

775.  Tar  Filler.  A  No.  5  or  No.  6  coal-tar  distillate  (§  698)  is 
often  used  as  an  interstitial  filler  for  brick  pavements.  The  bricks 
should  be  dry,  and  the  tar  should  be  applied  at  a  temperature  of 
300°  to  320°  Fahr.  by  being  poured  into  the  joints  with  a  vessel 
very  much  like  a  sprinkling  pot  without  the  rose.  The  success 
or  failure  of  the  tar  filling  depends  on  the  efficiency  and  care  of  the 
person  in  charge  of  heating  the  tar.  If  the  tar  be  too  hard, 
it  pulverizes  in  very  cold  weather;  if  it  be  too  soft,  it  runs  and 
becomes  sticky  in  very  hot  weather. 

The  cost  depends  upon  the  locality  and  the  closeness  of  the 
joints.  Usually  tar  costs  from  6  to  8  cents  a  gallon;  and  one 
gallon  is  generally  sufficient  for  one  square  yard  of  pavement.     The 


508  BRICK  PAVEMENTS.  [CHAP.  3 IV, 

total  cost  of  the  filler  varies  from  10  to  12  cents  per  square  yard  of 
pavement. 

Tar  is  superior  to  sand  in  that  it  makes  a  perfectly  water- 
tight joint;  and  it  is  superior  to  hydraulic-cement  grout  in  that 
it  is  not  so  rigid  and  therefore  makes  a  more  quiet  pavement. 
Tar  costs  more  than  sand,  and  does  not  protect  the  edges  of  the 
brick  as  well  as  hydraulic-cement  grout. 

The  objections  to  tar  are:  1.  In  summer  it  is  likely  to  melt  and 
run  out  of  the  joints;  and  in  winter  it  is  brittle  and  likely  to  chip 
out  of  the  joints.  2.  The  heating  of  it  makes  unpleasant  odors  on 
the  street. 

776.  Sometimes  asphalt  is  mixed  with  the  tar  to  make  it  less 
susceptible  to  changes  of  temperature,  and  sometimes  asphalt  is 
substituted  for  the  tar.  Unfortunately  a  mixture  of  tar  and  as- 
phalt is  often  referred  to  as  tar  and  also  as  asphalt,  and  frequently 
as  pitch — a  term  also  applied  to  tar  or  asphalt; — and  consequently 
it  is  difficult  to  determine  the  practice  in  different  cities.  A  com- 
mon composition  of  u asphalt "  filler  is:  refined  asphalt,  20  parts; 
residuum  oil,  3  parts;  and  coal-tar  distillate  No.  4,  100  parts.  It 
is  not  clear  that  using  a  thicker  tar  and  entirely  omitting  the  asphalt 
and  the  residuum  oil  would  not  give  an  equally  good  filler.  The 
different  asphalt  paving  companies  sell  an  asphalt  paving  filler. 

777.  Cement  Filler.  The  most  common  joint  filler,  other  than 
sand,  is  a  thin  mortar  composed  either  of  neat  Portland  cement 
or  of  1  part  cement  and  1  part  fine  sand,  the  latter  proportions 
being  the  more  common.  The  pavement  should  be  copiously 
sprinkled  immediately  before  the  grout  is  applied.  The  sand  and 
cement  should  be  mixed  in  batches,  say,  of  not  more  than  40  or  50 
pounds  of  each  at  one  time,  in  a  tight  mortar  box.  The  box  for 
this  purpose  should  be  3^  to  4  feet  long,  27  to  30  inches  wide,  and 
14  inches  deep,  and  should  have  legs  of  different  lengths,  so  that 
the  mixture  will  readily  flow  to  the  lower  edge  of  the  box,  which 
should  be  8  to  10  inches  above  the  pavement. 

The  sand  and  the  cement  should  first  be  mixed  dry,  and  when 
the  dry  mixture  assumes  an  even  and  unbroken  shade,  water  should 
be  added  in  a  sufficient  quantity  to  form  a  grout  of  the  consistency 
of  thin  cream.  The  grout  should  be  removed  from  the  box  to  the 
pavement  with  a  scoop  shovel,  and  not  by  overturning  the  box 


ART.  2.]  CONSTRUCTION.  509 

upon  the  pavement;  since  by  the  last  process  the  sand,  cement, 
and  water  are  separated,  and  are  deposited  in  different  portions  of 
the  pavement.  While  the  box  is  being  emptied,  the  grout  should 
be  constantly  stirred  to  prevent  a  separation  of  the  sand  from  the 
cement;  and  after  the  grout  has  been  applied  to  the  pavement,  it 
should  be  quickly  swept  into  the  joints  with  steel  brooms.  It  is 
better  that  the  joints  should  be  only  about  half  filled  at  the  first 
application,  since  then  there  is  a  less  depth  of  grout  in  the  joints 
and  consequently  less  liability  of  the  separation  of  the  sand,  the 
cement,  and  the  water. 

To  secure  the  best  results,  a  mortar  box  should  be  provided  for 
each  10  feet  of  width  of  street,  and  the  full  width  of  the  street  should 
be  filled  at  practically  the  same  time.  After  the  filling  has  been 
carried  forward  for  40  or  50  feet,  the  same  space  should  be  filled  again 
in  like  manner,  except  that  the  mixture  for  the  second  filling  should 
be  slightly  thicker  than  the  first.  The  joints  should  be  filled  en- 
tirely to  the  top  in  the  second  application.  After  the  joints  have 
thus  been  filled,  a  half  inch  of  fine  sand  should  be  spread  over  the 
entire  surface  of  the  pavement;  and  if  the  weather  is  very  hot  or 
dry,  the  sand  should  be  sprinkled  at  intervals  for  two  or  three  days, 
to  insure  that  the  cement  does  not  lose  by  vaporization  the  water 
necessary  for  chemical  combination  in  setting.  Traffic  should  be 
kept  off  the  pavement  from  seven  to  ten  days,  or  at  least  until  the 
cement  has  firmly  set.  If  the  cement  filler  is  disturbed  before 
it  is  fully  set,  it  is  practically  no  better  than  sand.  If  the  cement 
filler  is  put  in  as  described  above  and  allowed  to  set  firmly  before 
being  used,  it  will  wear  no  faster  than  the  best  paving  blocks  and 
will  prevent  spalling  and  chipping  of  the  bricks  at  the  edges  and 
corners. 

778.  The  amount  of  grout  required  will  vary  with  the  openness 
of  the  joints,  with  the  depth  of  the  grooves  (§  728),  and  also  with 
the  quantity  of  sand  of  the  cushion  coat  that  works  up  into  the 
lower  part  of  the  joints  while  the  bricks  are  being  rolled.  With  a 
2-inch  cushion  and  thorough  rolling  with  a  5-ton  roller,  the  sand 
will  be  forced  up  from  \  to  i  inch.  With  a  grout  mixed  1  to  1,  a 
barrel  of  cement  will  fill  from  25  to  40  square  yards;  and  with  a 
grout  composed  of  1  part  cement  and  1J  of  sand,  a  barrel  will  fill 
from  40  to  60  square  yards. 


510  BRICK  PAVEMENTS.  [CHAP.  XIV. 

If  the  grout  is  mixed  in  large  quantities  and  dumped  upon  the 
pavement,  it  will  require  about  one  hour  of  labor  for  each  25  square 
yards.  The  cost  of  labor  in  applying  the  grout  in  small  quantities 
as  described  in  §  777  varies  from  1  to  1.25  cents  per  square  yard. 
The  cost  of  the  cement  filler  will  depend  upon  the  price  of  cement 
and  the  care  employed  in  applying  the  grout.  With  ordinary 
re-pressed  blocks  and  reasonable  care  in  securing  close  joints,  the 
cost  of  a  1  to  1  Portland-cement  grout  will  usually  vary  from  8  to 
12  cents  per  square  yard.  If  the  grout  is  dumped  from  the  box 
upon  the  pavement,  the  cost  will  probably  be  from  8  to  10  cents 
per  square  yard ;  but  if  it  is  mixed  in  small  quantities  and  applied 
as  described  in  the  first  paragraph  of  §  777,  the  cost  will  probably 
be  10  to  12  cents. 

779.  The  advantage  of  the  cement  filler  is  that  it  protects  the 
edges  of  the  bricks  from  chipping,  and  thus  adds  to  the  durability 
of  the  pavement.  When  the  joints  are  filled  with  sand  or  tar,  the 
edges  of  the  brick  chip  off,  the  upper  faces  wear  round,  the  pave- 
ment becomes  rough,  and  the  impact  of  the  wheels  in  jolting  over 
the  surface  tends  to  destroy  the  brick;  while  with  a  good  cement 
filler,  the  edges  do  not  chip,  the  whole  surface  of  the  pavement  is 
a  smooth  mosaic  over  which  the  wheels  roll  without  jolt  or  jar,  and 
consequently  the  life  of  the  pavement  is  materially  increased. 

An  objection  to  the  cement  filler  is  that  it  does  not  take  up  the 
expansion  of  the  pavement  due  to  increase  of  temperature,  and  that 
consequently  the  pavement  is  likely  to  rise  from  the  foundation  and 
give  out  a  rumbling  noise  as  vehicles  go  over  it.  This  rumbling 
can  be  eliminated  by  inserting  special  expansion  joints  as  de- 
scribed in  §  786. 

Another  objection  to  the  cement  filler  is  that  in  making  repairs 
it  is  difficult  to  remove  the  brick  without  breaking  many,  and  it 
is  difficult  to  clean  the  brick  so  that  they  may  be  used  again.  This 
is  an  advantage,  if  it  will  in  any  degree  prevent  the  tearing  up  of 
the  pavement;  and  at  best  this  objection  ought  not  to  have  much 
weight  against  durable  construction. 

A  third  objection  is  that  the  street  can  not  be  used  while  the 
cement  is  setting.  Often  the  cement  is  not  allowed  to  set  fully 
before  throwing  the  street  open  to  traffic,  and  consequently  the 
chief  advantage  of  the  rigid  filler  is  lost. 


ART.   2.]  CONSTRUCTION.  511 

780.  Patent  Fillers.  There  are  a  number  of  joint-filling  com- 
pounds upon  the  market  whose  composition  either  is  a  secret  or 
is  protected  by  a  patent.  The  chief  components  of  some  of  these 
seem  to  be  tar  or  asphalt,  or  a  mixture  of  the  two;  while  others 
seem  to  be  composed  largely  of  hydraulic  cement.  It  has  not  been 
proved  that  any  of  these  compounds  are  either  better  or  cheaper 
than  Portland-cement  grout. 

781.  RUMBLING.  If  all  the  joints  of  a  brick  pavement  are 
filled  with  cement  grout,  vehicles  in  going  over  the  pavement  are 
likely  to  produce  a  considerable  rumble  or  roar,  due  apparently 
to  a  hollow  space  between  the  bricks  and  the  foundation.  At 
times  this  rumbling  is  very  pronounced.  It  is  most  common  in 
hot  weather,  but  occurs  also  in  cold  weather.  The  fact  of  this 
noise  and  its  remedy  are  more  clearly  established  than  its  cause. 
The  hollow  space  under  the  pavement  which  gives  rise  to  the  rum- 
bling may  be  due  to  any  one  of  three  distinct  causes,  viz.:  1,  ex- 
pansion of  the  pavement  due  to  an  increase  of  temperature;  2, 
crowding  inward  of  the  curbs  due  to  expansive  action  of  the  freez- 
ing water  in  the  soil  outside  of  the  curbs;  and  3,  shrinkage  of  the 
sand  cushion  due  to  its  drying  out. 

782.  In  hot  weather,  the  crown  of  the  pavement  may  be  lifted 
from  the  foundation  by  the  expansion  of  the  bricks  due  to  an 
increase  of  temperature.  This  can  occur  only  when  the  curbs  are 
firmly  enough  supported  to  serve  as  the  abutments  of  the  layer 
of  brick  when  acting  as  an  arch.  To  this  explanation  it  has  been 
objected  (a)  that  the  expansion  of  the  brick  would  be  insufficient 
to  produce  the  effect  and  (b)  that  the  single  course  of  brick  could 
not  act  as  an  arch  and  carry  a  loaded  vehicle. 

The  amount  and  force  of  expansion  of  a  brick  pavement  having 
cement-filled  joints  is  illustrated  by  the  fact  that  not  infrequently 
the  thrust  of  the  pavement  is  sufficient  to  force  the  curb  outward 
except  where  it  is  supported  by  the  walk  from  the  curb  to  the 
adjoining  property,  at  which  places  the  break  in  the  curb  makes 
manifest  its  movement.  Again,  in  pavements  having  all  of  the 
joints  filled  with  cement,  a  considerable  number  of  joints,  both 
transverse  and  longitudinal,  can  be  found  in  which  the  cement 
mortar  has  been  crushed  until  it  is  practically  only  so  much  sand. 
Further,  the  expansion  of  the  top  course  of  brick  is  frequently 


512  BKICK   PAVEMENTS.  [CHAP.   XIV. 

sufficient  to  lift  the  brick  from  the  foundation  and  form  a  ridge  in 
the  surface.  This  ridge  sometimes  runs  crosswise  of  the  street 
and  sometimes  lengthwise,  according  to  whether  it  is  due  to  longi- 
tudinal or  to  transverse  expansion.  If  the  ridge  is  only  an  inch 
or  two  high,  the  pavement  will  be  likely  to  settle  gradually  nearly 
or  quite  back  to  its  former  position,  without  material  damage; 
but  occasionally  the  ridge  rises  to  a  height  of  a  foot  or  more,  in 
which  case  a  crack  usually  opens  at  the  highest  point  and  finally 
a  considerable  strip  of  the  pavement  breaks  up,  some  of  the  bricks 
not  infrequently  being  thrown  several  feet  into  the  air. 

What  will  be  the  effect  of  a  difference  of  temperature  of  30°  F. 
on  a  brick  pavement  40  feet  wide  having  a  crown  of  6  inches? 
The  co-efficient  of  expansion  of  brick  is  0.000.003,4  for  1°  F.,*  and 
40  feet  for  a  difference  of  temperature  of  30°  F.  would  be  0.000,003,4 
X  30  X  40  X  12  =  0.049  inch.  If  the  pavement  lifts  from  its 
foundation  and  acts  as  an  arch,  its  own  weight  will  compress  the 
bricks  and  in  part  neutralize  the  expansion.  Owing  to  the  lack 
of  the  necessary  data  the  amount  of  this  compression  can  not  be 
computed  accurately.  The  pavement  if  4  inches  thick  will  weigh 
about  45  pounds  per  square  foot.  The  co-efficient  of  elasticity  of 
ordinary  brick  is  about  3,500,000  pounds  per  square  inch,f  and  of 
paving  brick  from  3,500,000  to  7,000,000  pounds  per  square  inch;  { 
the  co-efficient  of  elasticity  of  ordinary  Portland  cement  mortar  is 
about  1,500,000  pounds  per  square  inch.§  It  will  be  assumed  that 
the  co-efficient  of  elasticity  of  a  brick  pavement  is  4,000,000  pounds 
per  square  inch,  which  is  exact  enough  for  the  purpose  of  this  illus- 
tration. Considering  a  strip  of  the  pavement  1  foot  wide  and 
equating  the  moment  of  the  crown  thrust  and  the  moment  of  the 
weight  of  half  the  pavement,  we  find  that  the  compression  in  the 
arch  is  approximately  18,000  pounds.  If  the  thrust  is  uniformly 
distributed  it  is  equal  to  a  compression  of  practically  400  pounds 
per  square  inch,  and  will  produce   a  shortening  of  0.048  inch  in 

*  Annnal  Report  on  Tests  of  Metals  and  Other  Materials— report  of  tests  made 
with  the  U.  S.  government  testing  machine  at  the  Watertown  (Mass.)  Arsenal,— 
1896,  p.  367-69     The  result  quoted  is  the  mean  of  seventeen. 

f  Baker's  Masonry  Construction,  9th  edition,  p.  14 

%  Annual  Report  on  Tests  of  Metais  and  Other  Materials,  1896,  p.  348,  353,  358, 
359,  362,  364. 

§  Baker's  Masonry  Construction,  9th  edition,  p.  14. 


ART.   2.]  CONSTRUCTION.  513 

the  width  of  the  pavement.  This  shortening  is  almost  exactly 
the  expansion  for  a  change  of  30°  F.,  and  consequently  a  rise  of 
temperature  of  30°  would  be  required  to  neutralize  the  compression 
of  the  brick  due  to  the  arch  action  of  the  pavement,  and  any  ad- 
ditional increase  of  temperature  would  lift  the  brick  from  the 
foundation. 

Assuming  the  cross  section  of  the  surface  of  the  pavement  to  be 
an  arc  of  a  circle,  its  radius  is  approximately  400  ft.  The  differ- 
ence in  length  between  the  arc  and  the  chord  can  be  computed 
with  sufficient  accuracy  by  the  following  well-known  formula: 


24  r2 

in  which  a  equals  the  length  of  the  arc,  c  equals  the  length  of  the 
chord  (the  width  of  the  street),  and  r  equals  the  radius  of  curva- 
ture of  the  arc.  In  the  above  example,  the  length  of  the  arc  is 
0.192  inch  greater  than  the  width  of  the  street.  The  rise  at  the 
crown  is  practically  proportional  to  the  difference  in  length  between 
the  arc  and  its  chord.  The  expansion  for  20°  F.  is  0.000,003,4  X 
20  X  40  X  12  =  0.032,6  inch,  which  is  practically  one  sixth 
of  the  difference  between  the  normal  length  of  the  arc  and  the 
chord  of  a  40-foot  pavement  having  a  6-inch  crown..  Therefore 
an  increase  of  temperature  of  20°  above  the  30°  considered  in  the 
preceding  paragraph,  t.  e.,  a  total  rise  of  50°  F.,  will  lift  the  crown 
of  the  pavement  approximately  1  inch  from  the  foundation  pro- 
vided the  curbs  are  immovable. 

Of  course,  the  preceding  investigation  is  only  approximate, 
but  it  shows  the  possibility  of  a  pavement's  being  lifted  from  its 
foundation  through  the  action  of  heat.  Whether  or  not  the  pave- 
ment will  be  lifted  from  the  foundation  will  depend  upon  (1)  the 
solidity  of  the  curbs,  (2)  the  rigidity  of  the  filler,  (3)  the  thickness 
of  the  joints.  (4)  the  temperature  of  the  pavement  when  the  joints 
were  filled  (5)  the  maximum  temperature,  and  (6)  the  duration 
cf  the  high  temperature. 

If  the  bricks  lift  from  the  foundation,  why  does  not  the  very 
flat  arch  thus  formed  break  down  wrhen  a  heavy  vehicle  comes 
upon  it?  The  bricks  of  the  pavement  are  firmly  cemented  to- 
gether, and  the  whole  acts  somewhat  as  a  bent  beam,  and  there  is 


514  BRICK   PAVEMENTS.  [CHAP.   XIV. 

so  much  flexibility  in  this  brick  beam  that  it  deflects  and  touches 
the  foundation  at  points  sufficient  to  prevent  the  destruction  of 
the  arch,  and  still  is  unsupported  at  enough  points  to  give  out 
a  rumbling  sound. 

783.  In  cold  weather,  the  pavement  may  be  lifted  from  its 
foundation  by  the  freezing  of  the  water  in  the  earth  outside  of 
the  curbs  forcing  the  curbs  inward.  It  is  well  known  that  water 
in  freezing  expands  with  considerable  force;  and  if  each  curb  of  a 
40-foot  pavement  is  forced  ir  ward  -fa  of  an  inch,  the  crown  of  the 
pavement  will  be  lifted  more  than  an  inch  from  the  foundation. 
This  result  will  occur  only  when  the  subsoil  outside  of  the  curbs 
freezes  while  it  is  at  least  nearly  saturated  with  water. 

It  is  claimed  that  the  lifting  of  a  brick  pavement  in  cold 
weather  is  due  to  the  freezing  of  the  water  absorbed  by  the  brick. 
In  support  of  this  view  it  is  claimed  that  pavements  made  of  brick 
having  a  high  absorptive  power  more  frequently  give  out  a  rum- 
bling sound  than  those  made  of  brick  having  a  low  absorptive 
power.  The  theory  hardly  seems  plausible,  since  at  best  the  per 
cent  of  water  absorbed  is  very  small  and  its  expansion  would  be 
taken  up  to  a  considerable  extent  by  the  air  remaining  in  the  pores 
of  the  brick.  The  facts  offered  in  support  of  the  above  theory 
doubtless  have  some  other  interpretation. 

784.  Sometimes  spots  only  a  few  feet  in  diameter  give  out  a 
rumbling  sound;  and  on  account  of  the  limited  area  of  these  spots, 
the  rumbling  can  not  be  due  to  either  of  the  causes  discussed 
above.  These  spots  are  probably  due  to  a  shrinkage  of  the  sand 
cushion  by  its  drying  Out.  A  small  per  cent  of  water  adds  con- 
siderably to  the  volume  of  fine  sand,  and  hence  if  the  sand  cushion 
is  wet  when  laid  and  dries  out  after  the  cement  filler  has  set,  the 
brick  will  be  left  unsupported.  These  spots  disappear  with  the 
use  of  the  pavement — probably  by  the  breaking  of  the  cement' and 
the  settling  of  the  bricks. 

785.  It  is  claimed  that  the  rumbling  is  due  to  the  shrinkage  of 
the  concrete;  but  this  can  not  be  correct  as  the  bricks  are  not  laid 
until  the  concrete  is  firmly  set 

It  is  also  claimed  that  the  rumbling  is  due  to  large  pebbles  in 
a  thin  sand  cushion,  which  keep  the  bricks  from  obtaining  a  firm 
bed  in  the  sand;  but  this  is  at  least  doubtful,  since  such  pebbles 


ART.   2.] 


CONSTRUCTION". 


515 


would  probably  be  crushed  during  the  rolling,  and  besides  many 
such  pebbles  would  be  required  to  produce  the  observed  noise. 

786.  Expansion  Cushions.  The  rumbling  of  the  pavement 
(§  78!)  can  be  prevented  by  placing  a  tar- joint  from  J  to  1  inch  thick 
next  to  each  curb.  The  compression  of  the  tar  allows  the  bricks 
to  expand  without  lifting  the  pavement  from  its  foundation.  This 
tar-joint  can  be  inserted  by  setting  a  1-inch  board  next  to  the  curb 
before  laying  the  bricks,  and  then  after  the  bricks  are  laid  with- 
drawing it  and  filling  the  space  with  coal-tar  distillate  No.  5  or  6. 

The  longitudinal  expansion  can  be  taken  up  either  by  filling 
three  or  four  transverse  joints  with  tar,  each  25  or  30  feet,  or  by 
inserting  a  1-inch  tar-joint  each  40  or  50  feet. 

787.  In  one  case  a  1-inch  expansion  joint  at  each  curb  and  two 
transverse  tar-joints  every  50  feet  required  one  barrel  (50  gallons) 
of  tar  for  each  274  square  yards  of  a  pavement  36  feet  between 
curbs,  or  say  1  gallon  of  tar  for  each  5  or  6  square  yards  of  pave- 
ment, in.  another  case,  a  J-inch  expansion  joint  at  each  curb  and 
a  ^-inch  transverse  expansion  joint  at  each  35  feet  required  237 
gallons  of  tar  for  2,870  square  yards  of  pavement  or  1  gallon  for 
each  12  square  yards. 

788.  PERMISSIBLE  GRADES.  Table  50  shows  the  steepest 
grades  of  brick  pavement  in  actual  use  in  1900  in  the  cities  named. 

TABLE  50. 
Maximum  Grades  of  Brick  Pavements. 

City.  State.  Grade. 

Albany New  York 9.3  per  cent 

Baltimore Maryland 15 

Columbus Ohio. 9 

Des  Moines Iowa 11 

Erie Pennsylvania 7 

Joliet Illinois 6 

Mansfield Ohio 8 

Milwaukee Wisconsin •. 8 

Nashville Tennessee 7 

Parkersburg West  Virginia 15 

Peoria Illinois 8.4 

Philadelphia Pennsylvania 6 

St.  Joseph Missouri 10 

Toledo Ohio 5.6 

Troy New  York 7 

Wheeling West  Virginia 8 


516  BRICK  PAVEMENTS.  [CHAP.  XIV. 

' '  The  fact  that  such  steep  grades  are  in  use,  may  not  be  taken 
as  a  reason  for  imitation,  but  may  furnish  conclusive  reasons  for 
avoidance.  The  most  useful  information  on  the  subject  can  be 
obtained  from  teamsters  and  horsemen  of  these  cities.  If  it  is 
generally  agreed  that  certain  pavements  are  shunned  by  team- 
sters because  their  horses  slip  and  fall  when  going  down  a  certain 
street  with  a  load,  it  will  evidently  be  unwise  to  repeat  the  con- 
struction of  the  same  kind  of  pavement  with  an  equal  slope  in  a 
similar  climate.  An  examination  of  these  pavements  may  furnish 
to  the  observer  conclusive  reasons  for  or  against  copying  them, 
or  may  suggest  changes  in  detail  which  would  give  better  results. 
In  investigating  these  steep  grades,  it  should  be  bome  in  mind 
that  the  selection  of  the  pavement  for  a  given  street  may  have 
been  made  directly  or  indirectly  by  the  property  owners,  who  have 
not  necessarily  chosen  the  pavement  best  suited  to  attract  traffic, 
but  who,  preferring  a  quiet  street,  sometimes  select  a  pavement 
which  traffic  will  shun."  * 

789.  Merits  of  Brick  Pavements.  Bricks  as  a  paving 
material  have  some  attractive  features.  1.  They  may  be  had  in 
small  units  of  practically  uniform  size.  2.  They  may  be  had  in 
large  or  small  quantities.  3.  They  may  be  laid  rapidly  without 
special  expert  labor.  4.  When  ailing  pipes  or  other  causes  neces- 
sitate the  disturbance  of  the  pavement,  ordinary  tools  and  intelli- 
gence can  restore  the  original  surface.  5.  Brick  pavements  give 
a  good  foothold  for  horses.  6.  They  do  not  wear  slippery.  7. 
They  are  adapted  to  all  grades.  8.  They  have  low  tractive  resist- 
ance, particularly  if  the  joints  are  filled  with  Portland  cement 
grout.  9.  They  are  not  specially  noisy  when  properly  laid.  10. 
Brick  pavements  yield  little  mud  or  dust.  11.  They  are  easily 
cleaned.  12.  If  the  joints  are  filled  with  sand,  they  are  only 
slightly  absorbent;  and  if  filled  with  tar  or  cement,  they  are  non- 
absorbent.  13.  Brick  pavements  have  a  pleasing  appearance. 
14.  They  are  very  durable,  particularly  if  the  joints  are  filled  with 
Portland  cement.     15.  They  are  easily  repaired. 

790.  COST  OF  BRICK  PAVEMENTS.  The  cost  will  vary  with 
the  locality  and  the  details  of  construction,  and  consequently  any 

*City  Roads  and  Pavements,  by  William  P.  Judson.     Second  Edition.     193  p.. 
4''  X  6."    Published  by  the  author,  New  York  City,  1902. 


AET.  2.]  CONSTRUCTION.  517 

general  statement  of  cost  will  be  only  approximately  true  for  any 
particular  case. 

•The  grading  is  usually  done  by  the  cubic  yard;  and  the  cost 
varies  with  the  character  of  the  soil,  the  depth  to  be  removed,  the 
length  of  haul,  etc.  The  cost  of  grading  ranges  from  15  to  50 
cents  per  cubic  yard;  but  in  easy  soil  and  moderate  cuts,  it  gener- 
ally varies  from  20  to  30  cents.  It  usually  costs  2 J  to  3  cents  a 
square  yard  to  dress  off  the  subgrade  after  it  has  been  graded  with 
drag  or  wheel  scrapers,  and  to  throw  the  material  into  wagons. 

The  cost  of  rolling  the  subgrade  will  depend  upon  whether 
it  is  rolled  longitudinally  only  or  both  longitudinally  and  trans- 
versely. With  a  horse  roller  the  cost  of  labor  in  rolling  the  street 
longitudinally  will  probably  not  be  more  than  0.1  to  0.15  cent 
per  square  yard;  but  the  cost  on  account  of  interest  on  the  value 
of  the  roller  will  depend  upon  the  amount  of  work  done  per  year, 
and  may  be  from  £  to  1  cent  per  square  yard.  With  a  steam  roller 
the  cost  of  rolling,  both  transversely  and  longitudinally,  will  be 
about  0.5  cent  a  square  yard,  exclusive  of  interest,  storage,  and 
depreciation  of  the  roller. 

The  cost  of  the  concrete  will  vary  with  the  price  of  cement,  the 
proximity  of  broken  stone  or  gravel,  the  character  of  the  concrete, 
etc.  Ordinarily  the  materials  for  a  6-inch  course  will  cost  about 
40  cents  per  square  yard  (§  559),  and  the  labor  6  to  8  cents  per 
square  yard  (§  560). 

The  price  of  brick  varies  greatly  with  the  locality,  particularly 
with  the  freight  rate.  The  price  of  bricks  or  blocks  is  usually 
quoted  by  the  thousand  without  stating  the  size  or  number  re- 
quired to  lay  a  square  yard.  For  convenience  in  making  estimates 
and  comparisons,  Tables  51  and  52  are  given,  to  show  the  num- 
ber required  per  square  yard.  The  first  table  gives  the 
quantities  for  the  foundation  course,  and  the  second  for  the  top 
course.  In  Table  52,  the  upper  number  in  each  entry  is  for 
J-inch  joints,  which  is  perhaps  a  little  close  for  re-pressed  blocks; 
and  the  lower  number  is  for  |-inch  joints,  which  is  probably  a  little 
too  open  for  a  block  not  re-pressed.  The  price  of  bricks  per  thou- 
sand at  the  kiln  varies  from  $7.00  to  $15.00,  but  usually  from  $8.00 
to  $10.00;  and  assuming  the  size  to  be  2\"  X  4"  X  8£",  of  which 
54  not  re-pressed  are  required  to  lay  a  square  yard  of  pavement. 


518 


BRICK    PAVEMENTS. 


[CHAP.    XIV. 


TABLE  51. 
Number  of  Bricks  Required  for  One  Square  Yard  of 
Foundation  Course 
Brick  Laid  Flatwise  with  J-inch  Joints. 


Length  of  Brick, 
in  Inches. 

Width  of  Brick,  in  Inches. 

3* 

31 

3J 

ai 

4 

4fr 

•n      4? 

4* 

5 

71 

43.2 

41.8 

40.5 

39.3 

38.1 

37.0 

36.0 

35.1 

34.1 

30.9 

n 

42.5 

41.2 

39.9 

38.7 

37.6 

36.4 

35.4 

34.6 

33.6 

30.4 

8 

42.0 

40.5 

39.3 

38.1 

36.9 

35.9 

34.9 

34.0 

33.1 

29.9 

8£ 

41.3 

39.9 

38.7 

37.6 

36.4 

35.3 

34.4 

33.5 

32.6 

29.5 

8* 

40.6 

39.3 

38.1 

37.0 

35.9 

34.8 

33.9 

33.0 

32.1 

29.1 

8| 

40.1 

38.7 

37.6 

36.5 

35.4 

34.3 

33.4 

32.6 

31.6 

28.6 

8* 

39.5 

38.2 

37.0 

36.0 

34.8 

33.8 

32.9 

32.1 

31.1 

28.2 

8| 

38.9 

37.7 

36.5 

35.4 

34.4 

33.3 

32.5 

31.6 

30.7 

27.8 

8* 

38.4 

37.1 

36.0 

35.0 

33.9 

32.9 

32.0 

31.1 

30.3 

27.4 

8* 

37.9 

36.6 

35.5 

34.5 

33.4 

32.5 

31.5 

30.7 

29.9 

27.1 

9 

37.3 

36.1 

35.1 

34.0 

33.0 

32.0 

31.1 

30.3 

29.5 

26.7 

10 

33.8 

34.1 

31.6 

30.7 

29.7 

28.9 

28.1 

27.4 

26.6 

24.1 

the  cost  will  usually  vary  from  43  to  54  cents  a  square  yard  ex- 
clusive of  freight.  The  price  of  re-pressed  blocks  at  the  kiln  varies 
from  $12.00  to  $14.00  a  thousand;  and  assuming  the  size  to  be 
3"  X  4"  X  9"  of  which  46  are  required  to  lay  a  square  yard  (see 
Table  52),  the  cost  of  the  blocks  exclusive  of  freight  will  usually 
vary  from  55  to  65  cents  a  square  yard.  In  estimating  the  freight, 
it  may  be  helpful  to  know  that  a  brick  2"  X  4"  X  8"  will  weigh 
about  5  pounds,  and  one  2\"  X  4"  X  8J"  about  7  pounds,  and  a 
block  3"  X  4"  X  9"  about  9  pounds.  In  estimating  freight,  the 
fact  should  not  be  overlooked  that  for  one  reason  or  another  a  con- 
siderable number  of  bricks  are  rejected.  With  careful  grading  at 
the  kiln  the  broken  and  rejected  brick  is  likely  to  be  2  to  4  per  cent. 
The  cost  of  hauling  and  piling  on  the  side  of  the  street  is  about 


ART. 


CONSTRUCTION. 


519 


TABLE   52. 

Number  of  Bricks  Required  for  One  Square  Yard  of  Top  Course. 

The  upper  number  in  each  case  is  for  |-inch  joints,  and  the  lower  for 
^-inch  joints. 


Length 
of  Brick. 

Thickness  of  Brick,  in  Inches. 

Tnches. 

H 

_2_ 

77.6 
72.0 

2* 

73.2 
68.0 

2\ 

69.3 
64.8 

2* 

65.8 
61.8 

» 

2| 

21 

2|     !      3            4 

7! 

82.1 
76.2 

62.8 
58.9 

59.7 
56.4 

57.5 
54.0 

54.9 
52.0 

52.7 

49.8 

39.9 
38.1 

7* 

81.1 
75.3 

76.2 
70.8 

72.0 
67.2 

68.0 
63.9 

64.8 
60.8 

61.8 
58.1 

58.9 
55.4 

56.4 
53.1 

54.0 
51.1 

52.0 
49.1 

39.3 
37.6 

8 

80.1 
74.1 

75.3 

69.8 

70.8 
66.1, 

67.2 
62.9 

63.9 
60.0 

60.8 
57.0 

58.1 
54.4 

55.4 
52.5 

53.1 

50.8 

51.1 

48.4 

38.7 
36.9 

H 

78.5 
72.8 

74.1 

58.9 

69.8 
65.1 

66.1 
62.0 

62.9 
59.2 

60.0 
56.4 

57.1 
53.8 

54.4 
51.6 

52.5 
49.7 

50.4 
47.7 

38.1 
36.4 

8i 

77.1 
72.0 

72.8 
67.9 

58.9 
64.2 

65.1 
61.1 

62.0 
58.1 

59.2 
55.5 

56.4 
52.9 

53.8 
50.8 

51.6 

48.9 

49.7 
47.0 

37.6 
35.9 

81 

76.2 
70.8 

72.0 
66.8 

67.9 
63.2 

64.2 
60.0 

61.1 
57.4 

58.1 
54.7 

55  5 
52.3 

52.9 
50.0 

50.8 
48.2 

48.9 
46.3 

37.0 
35.3 

8| 

75.4 
69.7 

70.8 
65.8 

66.8 
62.3 

63.2 
59.2 

60.0 
56.6 

57.4 

53.8 

54.7 
51.4 

52.3 
49.3 

50.0 
47.5 

48.2 
45.7 

36.5 
34.8 

8f 

74.1 
68.9 

69.7 
64.8 

65.8 
61.4 

62.3 
58.4 

59.2 
55.9 

56.6 
53.1 

53.8 
50.6 

51.4 

48.7 

49.3 
46.8 

47.5 
45.1 

36.0 
34.4 

8! 

73.2 
67.9 

68.9 
63.8 

64.9 
60.6 

61.4 
576 

58.4 
54.9 

55.9 
52.5 

53.1 
50.0 

50.0 
48.0 

48.7 
46.1 

46.8 
44.4 

35.4 
34.0 

81 

72.0 
67.1 

67.9 
632 

63.8 
59.7 

60.6 
56.8 

57.6 
54.2 

54.9 
51.6 

52.5 
49.3 

50.8 
47.3 

48  0 
45.5 

46.0 
43.7 

35.0 
33.4 

9 

71.2 
66.1 

67.1 
62.3 

63.2 
58.9 

59.7 
56.1 

56.8 
53.6 

54.2 
51.0 

51.6 

48.7 

49.3 
46.8 

47.2 
44.9 

45.5 
43.1 

34.5 
33.0 

10 

64.1 
59.7 

60.3 
56.1 

58.6 
52.9 

53.8 
50.6 

51.2 

48.3 

4S.9 
45.9 

46.6 
44.1 

44.5 
42.2 

42.6 
40.5 

41.0 
38.9 

31.1 
29.7 

$1.00  per  thousand  for  a  haul  of  1  mile,  of  which  sum  about  half 
is  the  cost  of  loading  and  unloading  and  half  the  cost  of  team  and 
driver;  but  this  cost  for  team  and  driver  necessitates  the  use  of 
three  wagons  with  each  team. 


520  BRICK  PAVEMENTS.  [CHAP.  XIV. 

The  number  of  bricks  that  a  man  can  set  in  a  day  varies  with 
the  size  of  the  bricks  or  the  blocks.  An  average  laborer,  exclusive 
of  preparing  the  surface,  can  set  10,000  to  12,000  small  brick  in 
10  hours;  and  an  expert  will  set  15,000  in  10  hours.  "Under 
unfavorable  circumstances  nine  men  in  13  hours  prepared  the  sand 
bed,  set  the  brick,  and  completed  the  pavement  at  the  rate  of 
3,160  bricks  per  hour  per  man."  *  An  ordinary  laborer  can  set 
8,000  or  10,000  3"  X  4"  X  9"  blocks  in  10  hours,  and  a  good  man 
will  set  10,000  to  12,000. 

The  organization  of  a  paving  gang  is  usually  about  as  follows : 

1  man  in  charge  of  spreading  the  sand  cushion $2 .  50 

1  helper  on  the  sand  cushion 1 .  50 

6  men  wheeling  blocks  from  wagons 9 .  00 

4  men  setting  blocks 10 .  00 

1  man  sweeping  pavement  and  filling  joints  with  sand 1 .  50 

1  foreman  in  general  charge 5 .  00 

Total  per  day  of  10  hours $29.50 

This  gang  should  lay  at  least  1,000  square  yards  in  10  hours, 
and  under  very  favorable  conditions  should  lay  1,200  square  yards; 
and  consequently  the  cost  of  setting  the  brick  will  be  about  2?  to 
3  cents  per  square  yard.  If  the  brick  blocks  are  piled  upon  the 
side  of  the  street,  the  cost  of  laying  will  be  increased  2  or  3  cents 
per  square  yard,  owing  to  the  expense  of  first  piling  them  upon 
the  side  of  the  street  and  also  to  the  increased  cost  of  delivering 
the  blocks  to  the  setters.  Not  infrequently  the  total  cost  of  lay- 
ing the  brick  is  8  or  9  cents  per  square  yard ;  but  this  excessive 
cost  is  due  to  poor  management. 

In  a  particular  case,  80  hours  were  required  to  turn  the  chipped 
blocks  and  to  replace  the  rejected  blocks  with  good  ones,  in  1,633 
square  yards  of  pavement,  or,  say,  1  hour  for  each  20  square  yards. 
The  blocks  were  3"  X  4"  X  9",  and  about  2  per  cent  were  turned 
and  about  2  per  cent  were  rejected. 

The  cost  of  filling  the  joints  of  a  brick  pavement  is  about  as 
follows:  with  sand,  2  cents  per  square  yard  (§  774);  with  tar,  10  to 

*  Municipal  Engineering,  Vol.  3,  p.  129. 


ART.   2.]  CONSTRUCTION.  '       521 

12  cents  (§  775),  and  with  Portland-cement  grout  mixed  in  small 
quantities  and  dipped  upon  the  pavement,  10  to  12  cents  per 
square  yard  (§  777),  and  with  uniform  brick  and  care  in  getting  thin 
joints  may  be  only  9  or  10  cents. 

The  expansion  joints  will  require  a  gallon  of  tar  for  each  5  or  6 
square  yards  of  pavement  at  a  cost  of,  say,  8  cents  per  gallon,  or 
1J  cent  per  square  yard  of  pavement. 

A  summary  of  the  preceding  data  on  the  cost  of  brick  pave- 
ments is  as  follows: 

Ttitmq  Cost  per 

Items-  Sq.  Yd. 

Subgrade:  rolling $0 .002 

Concrete,  6  inches:  materials  (see  §  790) 40 

labor  laying 07 

Sand  cushion:  2  inches  of  sand  at  90  cents  per  cu.  yd 05 

labor  spreading 005 

Brick  blocks,  4  inches  deep:  f.  o.  b.  cars  at  destination 60 

hauling  to  the  street 04 

setting 03 

rolling 003 

turning  and  removing 01 

Filling  joints  with  sand  and  top  dressing - 02 

Total,  exclusive  of  administration,  tools,  profits,  etc $1 .27 

If  the  joints  are  to  be  filled  with  Portland-cement  grout  1  to  1 
in  the  best  manner  (see  §  777) ,  add  10  cents  per  square  yard  to  the 
above  for  the  grout  filling,  and  1J  cents  per  square  yard  for  the 
expansion  joints. 

791.  The  average  cost  of  17,000  square  yards  of  brick  pave- 
ment constructed  by  the  City  of  Minneapolis,  Minn.,  in  1897  by  the 
city's  force  is  given  below.*  The  foundation  consisted  of  6  inches 
of  concrete  composed  of  1  part  natural  cement,  2  parts  sand,  and 
5  parts  broken  stone.  The  sand  cushion  was  1  inch  thick.  The 
bricks  were  re-pressed,  and  were  made  in  Galesburg,  111.  They 
were  2\"  X  4"  X  8",  and  cost  $15.54  per  thousand,  or  87  cents 
per  square  yard,  f.  o.  b.  cars  Minneapolis.  The  joints  were  filled 
with  a  patent  filler,  under  contract  with  the  patentee.  Half-inch 
expansion  joints  were  inserted  across  the  street  about  150  feet 

*  Jour.  Assoc,  of  Engineering  Societies,  Vol.  20,  p.  235-38. 


522  BRICK    PAVEMENTS.  [CHAP.    XIV. 

apart.      The  wages  of   common   labor  were  $1.75  per  day,  and 
of  pavers  $2.00.     Teams  received  $3.50  per  day. 

Ttfms  Cost  per 

lTEMS-  Sq.  Yd. 

Removing  old  pavement $0 .  035 

Grading 0.032 

Concrete 0.467 

Planking  concrete,  lumber,  and  miscellaneous 0 .008 

Brick 0.870 

Hauling 0 .  038 

Sand  cushion 0 .  018 

Laying  brick * 0 .  032 

Murphy  joint  filler 0 .  175 

Total $1 .675 

792.  The  cost  of  brick  pavements  varies  greatly  with  the  lo- 
cality, chiefly  owing  to  the  difference  in  the  cost  of  transportation; 
but  in  the  states  of  Ohio,  Indiana,  Illinois,  and  Iowa,  and  the 
nearby  portions  of  the  adjoining  states,  the  cost  of  a  pavement 
composed  of  re-pressed  bricks  or  blocks  on  a  6-inch  concrete 
foundation  generally  ranges  from  $1.20  to  $1.70  per  square  yard.* 
If  no  concrete  is  required  for  a  foundation,  the  above  prices  may 
be  reduced  48  or  55  cents  per  square  yard. 

Art.  3.     Maintenance. 

793.  The  maintenance  of  a  brick  pavement  consists  in  watch- 
ing it,  especially  during  the  first  year  or  two,  to  see  that  no  de- 
pressions occur  due  to  insufficient  foundation  or  to  the  use  of 
defective  brick.  Any  low  place  due  either  to  the  settling  of  the 
foundation  or  to  the  wear  of  a  soft  brick,  is  rapidly  increased  both 
in  depth  and  in  area  by  the  impact  of  the  wheels  in  dropping  into 
the  hole.  When  any  unevenness  of  surface  from  either  of  these 
causes  appears,  it  should  be  at  once  rectified  before  the  pavement 
wears  unevenly. 

Brick  pavements  that  have  been  constructed  of  good  ma- 
terial and  have  been  kept  in  good  surface  during  their  early  use, 

*  For  the  cost  of  brick  paving  in  eighty-one  cities  during  the  years  1895-97, 
see  Proc.  Amer.  Soc.  Municipal  Improvements,  Vol.  4,  p.  138.  The  above  were 
years  of  great  industrial  depression,  and  hence  the  data  are  not  of  much  value. 


ART.  3.]  MAINTENANCE.  523 

wear  down  uniformly  and  keep  smooth  with  practically  no  expense 
for  repairs.  A  striking  example  of  this  is  seen  in  Terre  Haute,  Ind., 
a  city  having  a  population  in  1900  of  36,673,  where  a  brick  pave- 
ment having  a  concrete  base  and  cement-filled  joints,  on  the  prin- 
cipal business  street,  after  eleven  years  of  wear  without  any  re- 
pairs, is  nearly  as  smooth  as  a  marble  mosaic.  The  top  faces  of 
the  brick  are  flat,  and  the  joints  are  level  full  of  cement  grout. 
Scarcely  a  single  chipped  or  broken  brick  can  be  found;  and 
the  general  wear  in  the  middle  third  of  the  street  has  been  only 
about  eV  to  -J?  of  an  inch  of  depth,  with  a  very  few  holes  J  inch 
deep  caused  by  soft  brick.  Other  pavements  of  several  other  lots 
of  brick  that  have  been  in  service  a  shorter  time  are  proportionally 
as  durable.  The  brick  are  probably  not  as  good  as  those  made  at 
the  present  time;  but  the  pavement,  particularly  for  that  time, 
was  unusually  well  constructed.  It  was  provided  with  an  adequate 
foundation,  the  brick  were  well  burned,  and  were  carefully  and 
thoroughly  rolled,  and  the  joints  were  entirely  filled  with  good 
Portland-cement  grout,  and  consequently  this  pavement  has  worn 
exceedingly  well.  Of  course  other  pavements  constructed  with 
as  good  material  and  with  the  same  care  would  wear  equally 
well. 

794.  GUARANTEE.  Only  a  comparatively  few  cities  require 
a  guarantee  of  brick  pavements  (see  §  450).  Below  are  the 
specifications  employed  by  the  City  of  Buffalo,  N.  Y.,  to  determine 
whether  or  not  the  pavement  shall  be  repaired.  A  few  other 
cities  use  a  somewhat  similar,  but  less  severe,  specification. 

"During  the  period  of  maintenance,  whenever  the  surface  becomes  un- 
even, holding  water  more  than  one  eighth  inch  in  depth,  or  when  the  pave- 
ment has  settled  over  trenches,  or  heaved,  showing  a  variation  of  more  than 
three  eighths  inch  from  the  line  of  a  4-foot  straight  edge,  the  brick  shall  be 
then  taken  up  and  be  re-laid  at  proper  crown  and  grade.  If  in  any  continu- 
ous 300  lineal  feet  of  the  pavement,  it  is  found  necessary  to  repair  more  than 
one  third  of  the  area,  or  if  the  cracks  in  the  brick  exceed  the  proportion  of 
3  linear  feet  of  cracks  to  1  linear  foot  of  pavement,  all  the  brick  shall  then 
be  taken  up  in  the  area  included  in  the  300-foot  lines  and  the  curb  lines,  and 
shall  be  re-laid.  During  the  last  year  of  maintenance,  any  brick  in  the  pave- 
ment shall  show  not  less  than  one  half  the  original  width  or  thickness  of  such 
brick,  and  the  wear  or  abrasion  at  the  end  of  any  brick  shall  not  exceed 
more  than  three  fourths  of  an  inch  " 


524  BRICK    PAVEMENTS.  [CHAP.   XIV. 

795.  The  following  is  the  method  employed  by  the  City  of 
Albany,  N.  Y.,  in  1899. 

"  During  the  progress  of  the  work,  the  city  engineer  shall  weigh  not 
less  than  fifty  of  the  bricks  of  apparent  average  quality  and  appearance, 
and  file  a  certificate  of  the  result.  During  the  ten-year  guarantee  period,  the 
proper  officer  shall  take  up  and  re-weigh  fifty  brick  from  time  to  time,  and 
whenever  a  15  per  cent  loss  of  weight  is  found  in  any  bricks  on  the  street, 
they  must  be  replaced  with  bricks  as  nearly  as  possible  of  the  size  and 
quality  of  the  original." 


CHAPTER  XV. 
COBBLE-STONE  PAVEMENT. 

797.  A  cobble-stone  pavement  consists  of  cobble  stones  or 
small  bowlders  placed  side  by  side  upon  a  bed  of  sand  or  upon 
the  natural  soil.      Fig.  136  shows  a  transverse   section  of  such 


Fig.  136. — Section  of  Cobble-stone  Pavement. 

a  pavement.  The  earliest  pavements  in  many  of  the  older  Amer- 
ican cities  were  of  this  form,  and  until  recent  years  on  account  of 
their  comparatively  low  first  cost  were  quite  common.  In  1884, 
93  per  cent  of  all  the  pavements  in  Philadelphia  were  made  of 
cobble  stones;  but  in  1901  less  than  6  per  cent  were  of  this  kind. 
At  present  Baltimore  has  321  miles  of  cobble-stone  pavement, — 
more  than  any  other  city  in  the  United  States, — over  90  per  cent 
of  the  pavements  being  cobble  stones.  In  September,  1901,  New 
York  City  still  had  229  miles  of  streets  paved  with  cobble  stones, 
although  they  are  rapidly  being  replaced  with  better  pavements. 

525 


526  COBBLE-STONE    PAVEMENT.  [CHAP.   XV. 

Since  the  introduction  of  asphalt  and  brick  pavements,  and  since 
the  decrease  in  the  cost  of  stone-block  pavement  by  the  introduction 
of  improved  methods  of  quarrying,  and  since  the  decrease  in  the 
cost  of  crushed-stone  roads  by  the  invention  of  the  machine  rock- 
crusher  and  the  steam  road-roller,  there  is  little  excuse  for  the  con- 
struction of  cobble-stone  pavements.  The  construction  of  such 
pavements  have  been  practically  abandoned,  and  in  some  cities  it 
has  been  prohibited  by  law — like  theft  and  murder. 

However,  because  of  their  historic  interest  and  because  yards 
and  alleys,  and  also  gutters  and  crossings  of  unpaved  streets  are 
still  sometimes  paved  with  cobble  stones,  this  form  of  pavement 
will  be  briefly  considered.  The  ordinary  European  cobble-stone 
pavement  is  much  superior  to  that  of  this  country;  but  with  a  little 
care  a  cobble-stone  pavement  can  be  constructed  which  is  much 
superior  to  that  ordinarily  seen  in  American  cities. 

798.  GRADING.  The  earth,  stone,  and  other  materials  neces- 
ary  to  be  removed  should  be  taken  out  for  a  depth  of  12  inches 
below  the  top  line  of  the  finished  pavement.  All  spongy  material 
or  vegetable  matter  remaining  in  the  bed  should  be  removed  and 
be  re-placed  with  clean  sand  or  gravel,  which  should  be  well  com- 
pacted by  ramming  or  rolling.  Upon  the  subgiade  should  be 
spread  5  inches  of  clean  gravel,  which  should  be  firmly  tamped  or 
rolled.  Upon  this  gravel  bed  should  be  spread  a  3-inch  or  4-inch 
layer  of  loamy  sand  to  serve  as  a  bed  for  the  cobble  stones.  Loamy 
sand  holds  the  stones  better  than  that  which  is  perfectly  clean. 

799.  THE  STONES.  The  stones  should  be  hard,  durable 
cobble  or  kidney  stones,  not  less  than  4  inches  nor  more  than  6 
inches  long,  and  not  less  than  2  inches  nor  more  than  4  inches  in 
diameter.  They  should  be  sorted  as  they  are  brought  upon  the 
work,  and  the  several  sizes  should  be  piled  separately. 

800.  Setting  the  Stones.  The  work  should  proceed  up 
grade  and  from  the  gutter  toward  the  crown,  and  with  the  sides 
in  advance  of  the  center — so  that  the  stones  as  laid  will  tend  to 
crowd  together  and  not  apart.  The  paver  should  stand  upon  the 
stones  already  set,  and  should  disturb  the  sand  cushion  as  little  as 
possible.  With  the  hammer  shown  in  Fig.  137,  page  527,  the 
paver  makes  a  hole  into  which  he  sets  a  stone  with  its  long  axis 
vertical.      No  stone  is  to  be  laid  on  its  longest  side.     It  is  usual  to 


COST. 


527 


give  the  required  convexity  to  the  surface  by  placing  the  largest 

stones  in  the  middle  of  the  street,  and  suitably  graduating  the  sizes 

toward  the  sides.     The  stones  are  set  as  closely  and 

compactly  together  as   possible,  and   to   a    uniform 

grade;   and  should   break  joints  as   far   as  possible. 

After  the  stones  have  been  set,  all  joints  and  cavities 

should  be  filled  with  pebbles  and  paving  sand,  and 

then  the  pavement  should  be  carefully  and  thoroughly 

rammed  until   no  further    settlement  occurs.      The 

ramming  is  done  with  the  rammer  shown  in  Fig.  138, 

which  weighs  from  40  to  55  pounds.     If  in  ramming, 

any  of  the  stones  do  not  come  to  the  correct  grade, 

they  should  be  taken  out, 

re-set,  and  again  rammed. 

During  the  ramming  the 

joints  should  be  kept  full 

o  f    sand    and    pebbles ; 

and  when  the  ramming  is 

completed,  the  surface  of 

the  pavement  should  be 

covered  half  an  inch  deep  with  paving  sand. 

801.  COST.     The  following  is  the  cost  of  constructing  cobble- 
stone pavements  in  Baltimore,  Md.,  in  1901. 

Ttfm„  Cost  per 

1TEMS-  Sq.  Yd. 

Stones  at  $1.60  per  perch  of  2  800  lb $0 .  29 

Paving  sand  at  60  cents  per  cu  yd.,  delivered . . . ." 0 .  20 

Labor  laying  and  ramming . 

1  foreman  at  $3 .  00  for  8  hours  = $3 .  00 

4  pavers       "     3.00    "   8     "       - 12 . 00 

2  rammers  "     2.00    "8     "       = 4.00 

6  laborers    w      1 .66    "   8     "       = 10.00 


Fig.  137.— Cobble-stone 
Hammer. 


Fig.   138  — 

Cobble-stone 

Eammer. 


Total  for  200  sq.  yds.  = 29 .00 


0.14 


Total  cost  exclusive  of  administration,  tools  and  profits $0.63 

802.  MERITS  AND  DEFECTS.  Low  first  cost  is  the  only  merit 
of  a  cobble-stone  pavement.  It  is  unstable,  since  it  consists  of 
double-curved  surfaces  in  contact  at  points  only,  and  the  points 
of  contact  are  seldom  in  the  same  horizontal  plane.  Its  surface  is 
hard  to  maintain,  and  the  large  joints  are  receptacles  for  filth. 


CHAPTER  XVI. 
STONE-BLOCK   PAVEMENT. 

804.  NOMENCLATURE.  The  earliest  pavements  of  ancient 
times  consisted  of  irregular  dressed  blocks  of  stone  more  or  less 
accurately  fitted  together.  The  form  and  size  of  the  blocks  have 
varied  greatly  from  time  to  time,  a  fact  which  has  given  rise  to 
different  classes  of  pavements.  A  few  of  these  will  be  briefly 
described. 

805.  Roman  Roads.  The  Roman  roads  so  frequently  referred 
to  by  modern  writers  are  the  earliest  examples  of  stone-block 
pavements.  The  details  of  construction  varied  somewhat,  but  as 
a  rule  they  were  about  as  follows:  The  foundation  was  laid  in  a 
trench  about  3  feet  deep,  with  no  attempt  at  underdrainage. 
The  base  was  formed  of  one  or  sometimes  two  courses  of  large  flat 
stones  laid  in  lime  mortar,  and  was  usually  about  15  inches  thick. 
Upon  this  was  laid  a  9-inch  course  of.  small  fragments  of  stone 
imbedded  in  lime  mortar,  the  intention  of  this  course  apparently 
being  to  bind  together  the  tops  of  the  large  stones  in  the  course 
below.  Next  was  laid  a  6-inch  layer  of  concrete,  apparently 
to  make  a  smooth  bed  to  receive  the  stones  of  the  top  course. 
The  wearing  surface  consisted  of  closely-jointed,  irregular-shaped 
stones,  about  6  inches  thick.  The  total  thickness  of  the  road  was 
about  36  inches.  In  and  near  the  cities,  the  top  course  was  formed 
of  irregular  blocks  of  basalt,  porphyry,  or  lava  which  had  a  top  area 
of  4  or  5  square  feet  and  a  thickness  of  12  to  15  inches,  and  which 
were  dressed  and  fitted  together  with  extreme  accuracy  and  were 
imbedded  in  cement.  These  ancient  pavements  have  aptly  been 
described  as  "masonry  walls  laid  on  their  sides. " 

The  Romans  seem  to  have  located  their  roads  in  straight  lines, 
running  them  toward  prominent  land-marks  without  much  regard 

528 


NOMENCLATURE.  529 


to  the  topography  or  to  natural  obstacles.  They  were  wasteful  of 
materials  and  labor,  which,  however,  cost  nothing  but  the  lives 
of  captives  who  were  forced  to  build  these  roads  for  the  armies  of 
their  captors.  The  results  were  roads  which  are  remarkable  chiefly 
for  their  cost,  and  which  were  inferior  to  modern  pavements  cost- 
ing only  one  quarter  to  one  eighth  as  much.  The  durability  of 
these  roads  does  not  seem  so  remarkable  when  it  is  remembered 
that  the  traffic  was  light,  and  consisted  mostly  of  footmen,  unshod 
horses,  and  ox-carts  having  wooden  wheels,  and  also  that  probably 
the  surface  of  the  road  was  kept  covered  with  earth  two  or  three 
inches  deep. 

806.  Russ  Pavement.  The  earliest  dressed  stone-block  pave- 
ment in  this  country  was  the  Russ  patent  laid  on  Broadway,  New 
York  City,  in  1849.  This  consisted  of  a  6-inch  natural-cement 
concrete  foundation  on  which  was  laid  rectangular  granite  blocks, 
10  to  18  inches  long,  5  to  12  inches  wide,  and  10  inches  deep,  the 
sides  of  the  blocks  making  an  angle  of  45  degrees  with  the  line  of  the 
street. 

807.  Rubble  Paving.  In  some  cities  having  no  cobble  stones 
but  having  comparatively  plenty  of  even  bedded  sandstone  or 
limestone,  the  streets  were  paved  by  laying  rough  rubble  stones 
flatwise,  the  stones  being  4  to  6  inches  thick  and  having  a  top 
surface  of  4  to  6  square  feet.  The  irregular  joints  between  the 
stones  were  filled  with  spalls.  The  blocks  chipped  on  the  edges, 
wore  round  on  top,  and  readily  got  out  of  place,  thus  making  an 
exceedingly  rough  pavement. 

808.  Belgian  Block.  In  Europe  the  first  modern  pavements 
were  made  of  rectangular  blocks  having  several  square  feet  of  top 
surface,  which  were  laid  lengthwise  of  the  street;  but  as  traffic 
increased  it  was  found  that  the  long  joints,  being  parallel  to  the 
direction  of  the  travel,  rapidly  wore  into  ruts  and  the  pavement 
became  rough  and  uneven.  To  obviate  this,  the  blocks  were 
made  square  and  were  laid  with  their  sides  at  an  angle  of  45  degrees 
with  the  line  of  the  street.  It  was  soon  discovered,  however,  that 
large  blocks  were  not  suitable  for  heavy  traffic,  as  it  was  difficult  to 
bed  them  so  they  would  keep  their  place,  and  as  their  large  surface 
did  not  afford  a  good  foothold  for  horses.  This  led  to  the  use  of 
small  square  blocks  laid  with  their  edges  parallel  and  perpendicular 


530  STONE-BLOCK    PAVEMENT.  [CHAP.   XVI. 

to  the  line  of  the  street.  For  many  years  this  form  of  pavement 
has  been  very  common  in  the  cities  of  Europe,  the  blocks  usually 
having  a  top  surface  5  to  7  inches  square  and  a  depth  of  about  6 
inches.  This  form  of  pavement  seems  to  have  been  used  first  in 
the  city  of  Brussels,  Belgium;  and  in  this  country  is  known  as 
Belgian-block  pavement. 

The  Belgian  block  was  introduced  in  this  country  about  1850, 
and  for  a  time  was  much  employed.  The  objections  to  the  Bel- 
gian pavement  are:  1.  On  account  of  the  size  and  form  of  the 
blocks,  it  is  difficult  to  keep  them  in  place;  2,  the  blocks  are  of  such 
a  form  as  to  give  a  poor  foothold  to  horses;  and  3,  there  is  always 
a  considerable  length  of  joints  parallel  to  the  line  of  travel,  which 
causes  ruts  to  form  in  the  pavement.  Belgian  blocks  have  usually 
been  laid  with  their  sides  perpendicular  and  parallel  to  the  sides 
of  the  street;  but  if  a  square  block  is  to  be  used,  it  should  be  laid 
in  courses  diagonal  to  the  street,  so  that  no  joints  shall  be  parallel 
to  the  line  of  travel,  a  method  which  would  add  some  extra  expense. 
The  Belgian  block  has  been  discarded  in  this  country  for  the  ob- 
long block. 

809.  Guidet  Pavement.  This  pavement  consisted  of  stone 
blocks  having  a  hexagonal  top  surface,  the  joints  running  perpen- 
dicular to  the  street  being  comparatively  wide  and  those  parallel 
with  it  being  comparatively  narrow.  About  1869  a  considerable 
amount  of  this  pavement  was  laid  in  New  York  city  and  Brooklyn, 
at  a  cost  of  about  $7.00  per  square  yard. 

810.  Standard  Stone  Block.  At  present  the  only  stone  paving- 
blocks  employed  in  this  country  are  3  to  4  inches  wide,  8  to  10 
inches  long,  and  7  to  8  inches  deep,  and  these  are  laid  with  their 
longest  dimension  perpendicular  to  the  line  of  the  street. 

Stone-block  pavements  of  any  and  all  kinds  are  at  present  con- 
structed much  less  frequently  than  formerly,  brick  or  asphalt  being 
employed  instead;  but  it  is  probable  that  stone  blocks  will  con- 
tinue to  be  employed,  at  least  for  some  time,  on  heavy  traffic 
streets,  and  for  medium  traffic  streets  where  suitable  stone  is  plen- 
tiful and  brick  is  expensive. 


ART.   l.j  THE   STONE.  531 

Art.  1.    The  Stone. 

811.  As  stone-block  pavements  are  employed  only  where  the 
traffic  is  heavy,  the  material  of  which  the  blocks  are  made  should 
be  hard  enough  to  resist  the  abrasive  action  of  the  traffic,  and 
tough  enough  to  prevent  being  broken  by  the  impact  of  loaded 
wheels.  The  hardest  stones  will  not  necessarily  give  the  best 
results  in  the  pavement,  since  a  very  hard  stone  usually  wears 
smooth  and  becomes  slippery,  and  the  edges  of  the  block  chip  off 
and  the  upper  face  becomes  rounded,  thus  making  the  pavement 
very  rough.  A  hard  stone  may  be  necessary  under  a  heavy  traffic, 
but  under  medium  traffic  a  softer  stone  may  give  more  satisfactory 
results. 

The  stone  could  be  tested  to  determine  its  strength  and  dura- 
bility much  as  paving  bricks  are  tested,  but  it  is  not  known  that 
any  such  tests  have  been  made.  An  examination  of  a  stone  as  to 
its  structure,  the  closeness  of  its  grain,  its  homogeneity,  etc.,  may 
assist  in  forming  an  opinion  as  to  its  value  for  use  in  a  pavement; 
but  in  the  present  state  of  our  knowledge,  a  service  test  in  the 
pavement  is  the  only  certain  guide. 

Granite,  trap,  sandstone,  and  limestone  have  been  used  for 
paving  blocks. 

812.  GRANITE.  This  is  a  massive,  unstratified,  granular  rock 
composed  essentially  of  quartz  and  feldspar,  but  almost  always 
containing  other  components,  such  as  mica,  hornblende,  and  tour- 
maline in  varying  proportions.  The  quartz  and  the  feldspar  are 
called  essential  ingredients,  since  their  presence  is  necessary  to 
form  a  granite;  while  the  other  constituents  are  called  accessories, 
since  they  merely  determine  the  variety  of  the  granite.  The 
term  granite  is  popularly  applied  to  any  feldspathic  granular  rock, 
and  includes  gneiss,  syenite,  and  porphyry,  or  any  crystalline 
rock  whose  uses  are  the  same  as  granite.  Gneiss  is  a  rock  of  granitic 
composition  that  has  a  decided  banding  or  parallel  arrangement 
of  its  mineral  constituents.  Syenite  is  a  granitic  rock  containing 
no  quartz.  Porphyry  is  popularly  any  fine-grained  compact  rock 
having  large  crystals  scattered  throughout  its  mass. 

Granite  varies  in  texture  from  very  fine  and  homogeneous  to 
coarse  porphyritic  rocks  in  which  the  individual  grains  are  an 


532  STONE-BLOCK    PAVEMENT.  [CHAP.  XVi. 

inch  or  more  in  length.  The  color  may  be  red,  dark  mottled, 
light  to  dark  gray  or  almost  black.  The  durability  is  closely 
related  to  the  accessory  minerals  present;  and  although  granite 
is  popularly  regarded  as  the  hardest  and  most  durable  stone, 
there  are  some  notable  exceptions.  A  quartoze  granite,  one  in 
which  quartz  predominates,  is  too  brittle  for  paving  purposes; 
a  f  eld  spathic  granite,  one  containing  an  excess  of  feldspar,  is  too 
easily  decomposed;  and  a  micaceous  granite,  one  containing 
considerable  mica  in  parallel  lamina,  is  too  easily  split  for  use  in 
paving  blocks.  Gneiss  is  usually  too  much  stratified  to  make  a 
good  paving  material.  Syenite  is  one  of  the  best  materials  for 
paving  blocks,  and  usually  the  darker  the  color  the  better  the 
stone. 

The  average  specific  gravity  of  granite  is  2.66,  and  therefore 
the  stone  weighs  166^  pounds  per  cubic  foot,  or  practically  2  tons 
per  cubic  yard.  Granites  ordinarily  contain  about  0.8  per  cent  of 
water,  and  are  capable  of  absorbing  about  0.2  per  cent  more.  The 
crushing  strength  is  quite  variable,  but  usually  lies  between  15,000 
and  20,000  pounds  per  square  inch. 

A  most  important  property  possessed  by  all  granitic  rocks  is 
that  of  splitting  in  three  planes  at  right  angles  to  each  other,  so 
that  paving  blocks  may  readily  be  formed  with  at  least  nearly  plane 
faces  and  square  corners.  So  far  as  discovered,  this  valuable 
property  is  possessed  only  by  the  granitic  and  trappean  rocks. 
This  property  is  called  rift  or  cleavage,  and  was  caused  by  pressure 
before  the  rock  was  consolidated.  The  principal  rift  or  plane  of 
cleavage  is  always  perpendicular  to  the  line  of  pressure;  and  the 
character  of  the  rift  depends  upon  the  amount  of  pressure  ind 
the  grain  of  the  stone.  The  fine-grained  granites  possess  the  most 
perfect  rift,  and  it  decreases  as  the  size  of  the  grains  increase,  so 
that  a  coarse-grained  variety  is  likely  to  require  considerable 
dressing  to  bring  the  faces  of  the  blocks  to  a  plane  surface. 

813.  Granite  paving  blocks  are  produced  in  large  quantities 
in  Maine,  California,  Massachusetts,  Wisconsin,  Missouri,  New 
Jersey,  Pennsylvania,  South  Dakota,  New  Hampshire,  and  Georgia. 
The  order  in  the  above  list  is  that  of  the  number  of  blocks  produced 
in  1889,  the  first  two  states  producing  more  than  all  the  others.* 
*  Eleventh  Census  of  the  United  States. 


ART.  1.]  THE    STONE.  533 

In  the  last  few  years  the  production  of  granite  paving  blocks  has 
greatly  fallen  off,  apparently  more  than  one  half,  probably  owing 
to  the  substitution  of  asphalt  and  brick  for  stone  blocks  for  paving 
purposes. 

Maine,  New  Hampshire,  Massachusetts  and  Connecticut  abound 
in  granite  deposits  suitable  for  the  manufacture  of  paving  blocks, 
1 '  Rocks  of  a  similar  nature  occur  in  the  Blue  Ridge  section  of  the 
Appalachians  as  far  south  as  Georgia,  though  in  the  more  southern 
portions  of  the  region  the  process  of  decay  has  extended  so  deeply 
as  in  general  much  to  reduce  their  value  as  sources  of  paving 
blocks.  Still,  blocks  of  granite  of  good  quality  are  quarried  near 
Atlanta.  In  the  Cordilleran  district,  there  are  many  granite  rocks 
which  are  likely  in  time  to  serve  as  sources  of  paving  stone.  It  is 
probable  that  some  of  the  granite  materials  in  the  Ozark  district 
of  Arkansas  ma}''  also  serve  this  need." 

Granite  is  employed  for  paving  blocks  much  more  than  any 
other  variety  of  stone;  and  because  of  this  fact,  the  term  granite 
paving  is  generallly  used  as  being  synonymous  with  stone-block 
paving. 

814.  TRAP.  This  is  a  popular  term  applied  to  any  dark- 
colored,  massive,  igneous  rock.  There  are  twTo  varieties,  diabase 
and  basalt,  which  do  not  differ  materially  except  in  geological 
origin.  Trap  is  hard,  compact,  and  tough;  and  as  a  rule  is  finer- 
grained  than  granite,  but  is  not  so  easily  broken  into  regular  shapes. 
Diabase  is  found  in  large  quantities  in  the  Palisades  of  New  Jersey, 
and  to  some  extent  in  Connecticut  and  Pennsylvania;  and  basalt 
is  found  principally  wTest  of  the  Mississippi,  especially  in  California 
and  Oregon.  Owing  to  the  difficulty  of  making  them  trap  is  not 
much  used  for  paving  blocks. 

815.  SANDSTONE.  Sandstones  are  rocks  made  up  of  grains  of 
sand  which  are  cemented  together  by  siliceous,  ferruginous,  calca- 
reous, or  argillaceous  material.  In  most  cases  the  cementing  ma- 
terial determines  the  color,  the  various  shades  of  red  and  yellow 
being  due  to  iron  oxide,  the  purple  tints  to  oxide  of  manganese,  the 
gray  and  blue  tints  to  iron  in  the  form  of  ferrous  oxide  or  carbonate. 
The  texture  of  the  stone  varies  according  to  the  sizes  of  the  sand 
grains,  of  which  there  are  all  gradations  from  those  that  are  so  fine 
as  to  be  barely  discernible  to  those  that  are  very  coarse.     The 


534  STONE-BLOCK   PAVEMENT.  [CHAP.   XVL> 

hardness,  strength,  and  durability  of  the  stone  is  dependent  upon 
the  character  of  the  cementing  material.  Only  the  harder  and 
tougher  sandstones,  generally  those  in  which  the  cementing  ma- 
terial is  siliceous,  are  used  for  paving.  Sandstone  paving  blocks 
are  common  in  the  Lake  and  Western  cities.  The  principal  quar- 
ries from  which  sandstone  paving  blocks  are  obtained  will  be 
briefly  described. 

816.  Medina  Sandstone.  This  stone  is  found  in  the  state  of 
New  York,  extending  from  Oneida  and  Oswego  counties  on  the 
east  along  the  shores  of  Lake  Ontario  westerly  to  the  Niagara 
river.  It  continues  into  Canada,  and  is  found  also  to  some  extent 
in  Pennsylvania  and  Virginia.  It  is  generally  a  deep  brownish 
red  in  color,  though  sometimes  light  and  yellowish,  and  in  a  few 
localities  gray.  The  coloring  matter  is  oxide  of  iron.  It  is  both 
fine  grained  and  coarse  grained  in  texture,  the  latter  being  of  a 
deeper  color  as  the  iron  cement  more  easily  penetrates  the  inter- 
stices between  the  larger  grains.  The  principal  mineral  constituent 
is  quartz  associated  with  some  kaolinized  feldspar.  The  cementing 
material  is  mainly  oxide  of  iron  with  some  carbonate  of  lime.  The 
stone  is  evenly  bedded,  and  the  beds  are  divided  into  blocks  by 
systems  of  vertical  joints,  generally  at  right  angles  to  each  other, 
an  arrangement  which  greatly  facilitates  the  work  of  quarrying. 
It  has  a  specific  gravity  of  about  2.60,  and  consequently  it  weighs 
about  148  pounds  per  cubic  foot.  It  absorbs  2£  to  3J  per  cent  of 
water,  but  it  is  not  materially  affected  by  alternate  freezing  and 
thawing. 

This  stone  is  much  used  for  paving  in  the  Lake  cities,  where  it 
is  often  preferred  to  granite  since  it  does  not  wear  slippery. 

817.  Potsdam  Sandstone.  This  formation  is  worked  at  a 
number  of  places  in  the  state  of  New  York,  but  the  largest  quarries 
are  near  Potsdam.  In  general  the  stone  is  grayish,  yellow,  brown, 
and  sometimes  red  in  color,  according  to  the  amount  and  kind  of 
iron  in  composition ;  and  it  varies  in  texture  from  a  strong  compact 
quartzite  to  a  loosely  coherent  granular  mass.  That  quarried  at 
Potsdam  is  hard  and  compact,  evenly  grained,  and  reddish  in 
color.  It  is  largely  used  as  a  building  stone  and  to  a  considerable 
extent  also  for  pavements.  It  consists  almost  entirely  of  quartz 
and  the  cementing  material  is  almost  wholly  silica. 


ART.   1.]  THE    STONE.  535 

818.  Colorado  Sandstone.  In  Boulder  County,  Colorado,  are 
several  deposits  of  sandstone  that  furnish  stone  for  building  and 
also  for  paving  purposes.  The  stone  varies  in  color  from  gray  to 
a  light  red  according  to  the  composition  of  the  iron  compounds. 
It  is  found  in  layers  varying  from  J  inch  to  several  feet  in  thickness, 
splits  easily,  and  breaks  readily  at  right  angles,  so  that  it  is  formed 
into,  flagging,  curb  stones,  and  paving  blocks  without  difficulty. 
It  is  hard  and  tough,  and  wears  well  in  a  pavement.  Its  grain  and 
texture  are  such  that,  although  it  wears  smooth,  it  is  never  slip- 
pery ;  and  after  a  little  wear  it  forms  a  smooth  and  pleasing  pave- 
ment, very  similar  to  one  made  of  Medina  stone. 

819.  Sioux  Falls  Quartzite.  This  is  a  metamorphic  sandstone 
quarried  at  Sioux  Falls,  South  Dakota.  The  stone  is  almost  pure 
silica  with  only  enough  iron  oxide  to  give  it  color,  which  varies 
from  light  pink  to  jasper  red.  It  is  very  close  grained,  and  will 
take  a  polish  almost  like  glass.  It  is  said  to  be  the  hardest  stone 
in  this  country.  Its  crushing  strength  is  about  25,000  pounds 
per  square  inch.  It  possesses  a  remarkably  good  rift  and  grain, 
although  not  as  perfect  as  that  of  granite.  It  is  used  considerably 
as  a  paving  material,  being  shipped  as  far  east  as  Chicago;  but  it 
wears  smooth  with  a  glassy  surface. 

820.  Kettle  River  Sandstone.  This  is  a  fine-grained,  light- 
pink  sandstone,  found  in  large  quantities  at  Sandstone,  Minn., 
about  a  hundred  miles  north  of  Minneapolis,  which  has  been 
used  for  paving  purposes  in  Wisconsin  and  Minnesota.  The  stone 
wears  flat,  does  not  polish,  and  approaches  granite  in  its  resist- 
ance to  crushing. 

821.  LIMESTONES.  These  differ  greatly  in  structure,  from  a 
light  friable  variety  highly  charged  with  fossils  to  a  hard  compact 
rock  denser  and  heavier  than  granite.  They  also  vary  in  color 
according  to  the  iron  and  carbonaceous  compounds  that  may  be 
present.  The  thin  bedded  varieties  are  easily  broken  into  paving 
blocks.  Although  some  varieties  of  limestone  are  very  dense  and 
strong,  it  wears  unevenly  when  used  as  a  paving  material,  and  the 
blocks  are  speedily  shivered  by  traffic  and  split  by  frost,  owing  to 
the  fact  that  the  lamination  is  vertical. 


536 


STONE-BLOCK    PAVEMENT. 


[CHAP.   XVI. 


Art.  2.     Construction. 

Fig.  139  shows  a  transverse  section  of  the  better  form  of  stone- 
block  pavements. 


Fig.  139. — Section  of  Stone -block  Pavement. 

822.  FOUNDATION.  The  method  of  preparing  the  subgrade 
has  already  been  discussed — see  Art.  1,  Chapter  XII.  Formerly 
the  foundation  always  consisted  of  a  bed  of  sand  upon  the  natural 
soil  (§  565),  but  at  present  it  is  often  a  layer  of  concrete  (Art.  2, 
Chapter  XII).  The  sand  foundation  is  cheaper,  but  with  it  the 
pavement  does  not  keep  its  surface.  At  present  stone-block 
paving  is  laid  only  on  streets  subject  to  heavy  traffic,  in  which 
case  a  concrete  foundation  is  specially  desirable.  Of  course,  if  the 
subsoil  is  solid  and  not  easily  affected  by  moisture,  it  may  be  suffi- 
cient to  lay  the  blocks  upon  the  natural  soil;  but  on  account  of 
the  heavy  traffic  which  stone  blocks  are  intended  to  support,  it 
is  seldom  wise  to  dispense  with  a  concrete  foundation. 

823.  SAND  CUSHION.  The  thickness  of  the  bed  of  sand  upon 
which  the  blocks  are  laid  should  vary  with  the  regularity  of  form 
of  the  blocks.  Experience  with  brick  pavements  has  abundantly 
proved  that  the  sand  cushion  should  be  2  inches  thick ;  and  as  stone 
blocks  are  never  as  regular  in  form  as  brick  blocks,  the  sand  cushion 
for  the  former  should  never  be  less  than  2  or  2\  inches,  so  as  to  give 
sufficient  depth  to  bring  the  top  of  the  blocks  to  a  uniform  surface. 


ART.  2.J  CONSTRUCTION".  537 

A  2-inch  sand  cushion  is  usually  employed,  but  experience  with 
brick  pavements  seems  to  indicate  that  a  thicker  cushion  would 
give  a  smoother  pavement.  The  sand  should  be  fine,  clean,  dry, 
and  sharp.  The  sand  should  be  fine,  so  as  to  make  a  smooth  bed; 
should  contain  no  clay  or  loam,  so  as  not  to  be  affected  by 
moisture;  should  contain  no  organic  matter  so  as  to  be  incom- 
pressible; should  be  dry,  so  as  to  pack  well;  and  should  be  sharp, 
since  it  is  then  less  mobile.  No  great  care  is  required  in  spreading 
the  sand  cushion,  since  it  is  likely  to  be  considerabfy  disturbed  in 
setting  the  blocks.  The  sand  is  usually  spread  with  shovels — 
compare  §  763. 

824.  THE  BLOCKS.  The  blocks  should  be  made  of  sound  and 
durable  stone,  free  from  weather  marks  and  seams,  and  should 
be  of  uniform  hardness,  since  the  pavement  will  wear  unevenly  if 
hard  and  soft  blocks  are  laid  together.  For  the  appearance  of  the 
pavement,  it  is  desirable  that  blocks  of  only  one  color  be  laid  to- 
gether. 

825.  Dressing.  The  blocks  should  be  split  and  dressed  so  as 
to  have  as  nearly  as  possible  plane  rectangular  faces  and  square 
corners.  There  is  a  marked  difference  in  the  regularity  of  paving 
blocks  of  different  varieties  of  stone  and  also  from  different  quar- 
ries of  the  same  variety.  As  a  rule  stone  paving-blocks  are  more 
carefully  dressed  in  Europe  than  in  America,  but  recently  more 
attention  has  been  given  in  this  country  to  the  form  of  the  blocks. 
The  more  regular  the  blocks  the  thinner  the  joints,  and  consequently 
the  smoother  and  more  durable  the  pavement.  In  a  general  way, 
the  ordinary  stone-block  pavement  in  this  country  has  joints  from 
\  to  1  inch  wide  with  an  average  of  about  f  inch,  while  some  of 
the  better  constructed  pavements  recently  made  have  joints  from 
}  to  \  inch  wide  with  an  average  of  about  |  inch.  The  surface  of  a 
recently  finished  pavement  laid  with  ordinary  blocks  will  show 
depressions  of  about  1  inch  under  a  3-foot  straight  edge  laid  par- 
allel to  the  curb,  while  the  most  carefully  dressed  blocks  will  show 
about  \  inch.  Of  course,  these  limits  vary  considerably  with  the 
variety  of  the  stone.  The  two  grades  of  paving  as  above  are 
very  common,  the  former  being  called  ordinary  stone  block,  and 
the  latter  specially  dressed  stone  block. 

The  blocks  should  not  taper  much  in  any  direction;  and  for 


5,38  STONE-BLOCK    PAVEMENT.  [CHAP.   XVI. 

ordinary  blocks  it  is  often  specified  that  the  length  of  a  block  shall 
not  differ  at  top  and  bottom  by  more  than  1  inch,  the  width  by 
more  than  £  inch,  and  the  depth  by  not  more  than  J  inch.  The 
faces  should  be  free  from  lumps  or  bunches;  and  for  ordinarv 
blocks  it  is  often  specified  that  there  shall  be  no  projection  greater 
than  \  inch,  and  for  specially  dressed  blocks  J  inch. 

826.  Size  of  Blocks.  There  has  been  much  discussion  as  to  the 
best  dimensions  for  stone  paving-blocks;  but  the  proper  size  is  a 
matter  of  judgment  and  does  not  admit  of  determination  except 
within  limits. 

The  width  should  be  such  as  to  give  a  good  foothold  for  horses; 
and  since  the  horse  must  depend  for  a  foothold  chiefly  upon  the 
shoe-calks'  catching  in  the  transverse  joints  of  the  pavement,  the 
width  of  a  block  should  be  about  equal  to  the  distance  between 
the  toe  and  the  heel  calks  of  a  horse's  shoe.  On  the  other  hand,  if 
the  blocks  are  too  narrow  the  number  of  transverse  joints  wall  be 
unduly  increased  and  the  pavement  will  wear  rapidly  and  be- 
come rough. 

The  block  should  not  be  so  long  that  it  will  fail  to  conform 
to  the  surface  of  the  pavement,  nor  so  short  as  to  make  too  many 
longitudinal  joints. 

The  depth  should  be  sufficient  to  keep  the  block  in  position. 
It  is  usually  assumed  that  this  is  6  inches,  but  the  stability  of  the 
block  varies  greatly  with  the  manner  of  filling  the  joints  (§  832), 
and  it  is  quite  probable  that  since  the  substitution  of  tar  or  hy- 
draulic cement  as  a  joint  filling  material  a  less  depth  would  suffice. 
Not  infrequently  the  depth  is  made  greater  than  is  necessary  for 
stability,  to  allow  for  wear;  but  before  any  considerable  depth  is 
worn  away,  the  blocks  become  very  uneven  and  rough,  and  the 
pavement  should  be  re-laid.  The  blocks  may  then  be  taken  up, 
and  be  re-dressed,  and  be  laid  again.  In  America  the  depth  of 
adjoining  blocks  is  usually  allowed  to  vary  as  much  as  1  inch, 
while  in  England  the  limit  is  \  inch.  The  wide  variation  in  the 
depth  of  adjoining  blocks  is  the  most  common  cause  of  the  great 
roughness  of  ordinary  stone-block  pavements,  the  shorter  block 
having  the  greater  depth  of  sand  under  it  settles  more  than  its 
deeper  neighbor. 


ART.  2.] 


CONSTRUCTION. 


539 


Table  53  gives  the  dimensions  of  stone  paving-blocks  employed 
in  various  cities. 


TABLE  53. 

Sizes  of  Stone  Paving-blocks. 


Ref. 

No. 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 


19 
20 
21 
22 
23 
24 
25 
26 


Cities. 


American 

Albany,  N.  Y 

Baltimore,  Md 

Boston,  Mass.,  small... 
"  "       large  .  . 

Buffalo,  N.  Y 

Cambridge,  Mass 

Chicago,  111 

Cincinnati,  O 

Cleveland,  O 

Columbus,  O 

New  Haven,  Conn 

Newark,  N.  J 

New  York,  N.  Y 

Philadelphia,  Pa 

Pittsburgh,  Pa 

Providence,  R.  I 

St.  Louis,  Mo 

Washington,  D.  C.  . . . 

Foreign : 

Berlin 

Liverpool 

London  

Manchester 

Paris,  large 

"       medium 

"       small 

Vienna 


Dimensions,  in  Inches. 


Width. 


3  -U 
3  -4" 
34-4 

34-44 
3  -4f 
34-4 

34-44 
3  -44 
31-5 
3  -5 
34-44 
34-4* 
34-4* 
34-4* 
3*-4* 
3  -4 
34-44 
3  -5 


74-7f 

31 
3  -44 
3  -34 
61-9 
54-7 
41-54 

71 


Length. 


8  -14 

9  -12 

6-8 
8  -12 

7  -12 
7-8 

8  -10 
8  -12 
8  -13 
6  -12 
8  -14 
8  -12 
8  -12 
8  -12 
6  -10 

8  -12 

9  -12 
6-8 


74-71 

31 
8  -14 
5-7 

9 
6-8 
6-8 

71 


Depth. 


7  -8 
6  -7 
74-8 
74-8 
64-7 
74-8 

6 
6  -7 
6  -64 

6  -7 

7  -8 
7  -8 
7  -8 
6  -64 

6  -7 

7  -8 

74-84 

54-6 


61 

6 

6  -64 

9 

6  -8 

41-7 

71 


827.  Usually  the  contractor  buys  the  blocks  by  the  thousand, 
but  gets  paid  for  them  by  the  square  yard;  and  therefore  it  is  to 
his  financial  advantage  to  use  as  many  large  blocks  as  possible. 
Again,  the  man  who  sets  the  blocks  is  usually  paid  by  the  square 
yard,  and  therefore  it  is  to  his  financial  advantage  to  make  the 
joints  as  wide  as  he  may.  It  is  very  undesirable  that  it  should  be 
to  the  financial  interests  of  the  contractor  and  of  the  paver  to 
secure  a  poor  pavement,  i.  e.,  one  having  large  blocks  and  wide 
joints.     An  excess  in  the  width  of  the  block  is  more  important  than 


540  STONE-BLOCK    PAVEMENT.  [CHAP.  XVI. 


in  the  length,  since  it  is  proportionally  a  larger  matter,  and  also 
since  it  has  a  more  important  influence  upon  the  quality  of  the 
pavement;  and  therefore  special  care  should  be  taken  to  prevent 
an  excessive  width  of  blocks  or  too  thick  side-joints.  To  identify 
as  far  as  possible  the  interests  of  the  contractor  with  those  of  the 
city,  the  following  method  of  measuring  a  stone-block  pavement 
has  been  proposed.* 

"The  blocks  must  be  substantially  smooth  and  square  on  all  their  faces, 
and  within  the  limits  of  the  following  dimensions:  Not  less  than  3£  inches* 
nor  more  than  4^  inches  wide  across  their  upper  and  lower  faces;  not  less 
than  7  nor  more  than  8  inches  deep;  and  not  less  than  8  nor  more  than  14 
inches  long,  except  where  shorter  stones  are  necessary  to  fill  out  courses. 

"The  sum  to  be  paid  per  square  yard  shall  be  ascertained  as  follows:  The 
number  of  blocks  per  square  yard  upon  which  the  bid  of  the  contractor  is 
based  shall  be  22|.  The  actual  average  number  of  blocks  laid  per  square 
yard  shall  be  determined  as  follows:  The  City  Engineer  shall  from  time  to 
time,  during  the  progress  of  the  work,  measure  the  width  of  50  to  100 
courses,  and  from  this  deduce  the  average  width  of  a  course.  The  average 
length  of  the  blocks  is  hereby  fixed  for  the  purpose  of  computing  the 
number  of  blocks  laid  per  square  yard,  at  12J  inches. f 

"  For  each  block  or  fractional  part  thereof  that  the  average  number  laid 
per  square  yard  shall  exceed  22£,  there  shall  be  added  to  the  contractor's 
bid  per  square  yard  an  amount  computed  at  the  rate  of  9^  cents  per  block. 
For  each  block  or  fractional  part  thereof,  that  the  average  number  laid  per 
square  yard  shall  fall  short  of  22\,  there  shall  be  deducted  from  the  con- 
tractor's bid  per  square  yard  an  amount  computed  at  the  rate  of  9J  cents 
per  block." 

According  to  this  method,  if  the  contractor  uses  narrow  blocks 
and  thin  joints,  the  price  per  square  yard  is  proportionally  in- 
creased; but  if  he  uses  thick  blocks  and  wide  joints,  the  price  per 
yard  is  decreased.  To  meet  the  case  in  which  a  contractor  should 
buy  large  blocks  at  a  considerable  reduction,  it  might  be  wise  to 
make  the  amount  per  block  to  be  deducted  greater  than  that  added. 
For  convenience  in  applying  the  above  method,  a  table  is  computed 
which  gives  in  one  column  the  width  of  50  courses  and  in  a  second 
column  the  corresponding  number  of  blocks  per  square  yard.     Of 


*  By  Horace  Andrews,  City  Engineer  of  Albany,  N.  Y.,  in  1890  in  Engineering 
Record,  Vol.  21,  p.  314  and  329 ;  Vol.  25,  p.  110-11. 

fThis  value  was  determined  by  measuring  a  number  of  blocks  in  pavements 
laid  with  blocks  of  the  size  stated  above. 


ART.   2.]  CONSTRUCTION".  541 

course,  the  number  of  blocks  to  a  square  yard  would  vary  with 
the  specified  dimensions  of  the  blocks  and  with  the  width  of  joints, 
which  latter  would  vary  with  the  different  kinds  of  stone  and  even 
with  the  same  kind  from  different  quarries,  and  could  be  deter- 
mined in  any  particular  case  only  by  measuring  the  combined 
width  of  a  number  of  courses  of  blocks  in  the  pavement.  The 
normal  or  contract  number  of  blocks  per  square  yard  should  be 
stated  according  to  the  quality  of  work  desired. 

Some  cities  buy  the  blocks  and  contract  for  laying  them,  a 
method  which  eliminates  the  interest  of  the  contractor  in  using 
large  blocks.  In  some  cities  it  is  the  custom  for  the  contractor  to 
buy  the  blocks  by  the  square  yard  in  the  pavement,  in  which  case 
the  contractor  pays  only  for  the  blocks  accepted,  and  has  no  finan- 
cial interest  in  the  size  of  the  blocks  or  the  thickness  of  the  joints. 
In  Great  Britain  it  is  customary  to  buy  the  blocks  by  weight,  a 
method  which  eliminates  any  interest  of  the  contractor  in  the  size 
of  the  blocks. 

828.  Some  cities  require  the  blocks  to  be  inspected  and  sorted 
to  sizes  before  being  piled  on  the  street.  The  advantages  of  this 
are:  (1)  when  stacked  upon  the  street,  only  the  outside  blocks  of 
the  pile  can  be  inspected;  (2)  when  the  blocks  are  being  laid,  the 
inspector  has  enough  to  do  to  watch  the  quality  of  the  workman- 
ship without  having  also  to  inspect  the  blocks;  (3)  removing 
rejected  blocks  from  the  pavement  delays  the  opening  of  the  street; 
and  (4)  if  the  blocks  are  sorted  before  being  piled  upon  the  street, 
different  sizes  are  not  so  likely  to  get  into  the  same  course,  and 
therefore  the  joints  will  be  narrower. 

In  Cleveland,  Ohio,  where  the  specified  width  of  the  stone 
paving-block  is  from  3J  to  5  inches,  the  blocks  are  sorted  into  three 
classes.  Class  No.  1  includes  blocks  from  S\  to  3J  inches,  Class 
No.  2  blocks  from  3|  to  4|  inches,  and  Class  No.  3  embraces  blocks 
from  4J  to  5  inches.  Blocks  in  Class  No.  1  are  marked  with  red 
paint,  blocks  in  Class  No.  2  with  blue  paint  and  those  in  Class  No. 
3  with  black  paint,  so  that  when  the  blocks  are  delivered  on  the 
street  each  class  can  be  easily  recognized  and  laid  by  themselves 
in  the  pavement. 

Some  cities  specify  that  thinner  blocks  shall  be  used  on  steep 
grades  than  on  level  portions,  to  improve  the  foothold. 


542  STOXE-BLOCK    PAVEMEXT.  [CHAP.   XVI. 

829.  SETTING  THE  BLOCKS.  In  placing  the  blocks,  the  work- 
man should  stand  upon  the  finished  work,  that  the  sand  cushion 

may  not  be  disturbed;  but  he  usually 
stands  on  the  sand  cushion,  the  blocks 
being  piled  on  the  sand  bed  behind 
the  paver.  The  workman  with  the 
Fig.  140,-Stone  paver's  Hammer,   pointed  end  6i  the  hammer  shown  in 

Fig.  140,  excavates  a  hole,  if  need  be, 
into  which  to  set  the  block. 

To  secure  the  proper  form  to  the  surface  of  the  pavement,  a 
chalk  line  is  made  upon  each  curb  or  a  string  is  stretched  in  each 
gutter  to  indicate  the  top  of  the  blocks,  and  a  row  of  blocks  20  to  25 
feet  apart  is  set  in  the  center  of  the  street  with  their  tops  to  grade, 
as  determined  by  measuring  down  from  a  string  stretched  from 
curb  to  curb.  If  the  street  is  wide,  one  or  more  rows  of  blocks 
are  placed  between  the  curb  and  the  crown.  Ordinarily  the  sur- 
face of  the  pavement  is  brought  to  grade  between  the  guide  blocks 
with  the  unaided  eye;  but  in  the  best  work,  a  straight  edge  or 
string  is  placed  parallel  to  the  line  of  the  street  on  the  guide  blocks, 
by  which  to  grade  the  surface,  and  between  these  lines  the  blocks 
are  brought  to  the  surface  indicated  by  a  straight  edge  parallel  to 
the  line  of  the  street  resting  upon  the  pavement  already  completed. 

The  blocks  should  be  set  with  their  long  dimension  across  the 
street,  except  at  street  intersections;  and  should  be  placed  in 
straight  rows  with  as  close  joints  as  possible.  Each  course  should 
be  formed  of  blocks  of  uniform  width  and  depth;  and  the  bond 
should  be  approximately  half  the  length  of  a  block,  or  at  least  3 
inches.  As  the  blocks  are  of  uneven  lengths,  the  securing  of  the 
proper  bond  will  require  careful  attention.  The  paver  is  instructed 
to  secure  thin  joints,  and  consequently  has  a  tendency  to  set  the 
block  with  the  larger  end  up;  but  when  set  in  this  way  the  block 
will  surely  sink  under  traffic.  Placing  the  large  end  of  the  block 
down  makes  a  wide  joint,  which  is  objectionable  if  the  joints  are 
to  be  filled  only  with  sand  and  pebbles  (see  §  832),  but  is  no  serious 
objection  if  the  joints  are  to  be  filled  with  hydraulic-cement  grout 
(see  §  832). 

The  courses  at  street  intersections  are  arranged  substantially 
as  in  brick  pavements  (see  §  768).     The  work  should  progress  up 


ART.  2.] 


CONSTRUCTION, 


543 


grade  and  from  the  gutter  towards  the  crown,  so  that  the  blocks 
may  have  no  tendency  to  settle  away  from  each  other  and  thus 
increase  the  width  of  the  joints. 

830.  RAMMING  THE  BLOCKS.  After  the  blocks  have  been 
placed,  they  should  be  thoroughly  rammed  until  they  come  to  a 
firm  bearing.  As  a  rule  the  workman  is 
more  interested  in  securing  a  uniform  sur- 
face than  in  bringing  the  blocks  to  an  un- 
yielding bearing.  Each  block  should  re- 
ceive at  least  three  hard  blows  —  one 
near  each  end  and  one  in  the  middle.  The 
rammer  employed,  Fig.  141,  weighs  from 
50  to  90  pounds,  ordinarily  60  to  75  pounds. 

If,  after  being  rammed,  a  block  does 
not  conform  to  the  general  surface  of  the 
pavement,  it  should  be  lifted  out,  and 
sand  should  be  added  to  the  sand  bed  or 
extracted  from  it  to  bring  the  top  of  the 
block  to  the  proper  elevation.  Any 
imperfect  or  broken  blocks  should  be 
removed  and  be  replaced  with  perfect 
ones.  Finally  each  block  should  be  ad- 
justed so  that  it  stands  perpendicular  to 

the  sand  bed  and  has  its  top  face  conforming  to  the  surface  of 
the  pavement.  The  quality  of  the  pavement  depends  largely 
upon  the  care  with  which  this  adjustment  is  made. 

To  secure  a  thorough  ramming  of  the  pavement,  it  is  sometimes 
specified  that  there  shall  be  one  rammer  to  each  paver,  and  occa- 
sionally one  rammer  to  two  pavers.  No  ramming  should  be  al- 
lowed within  20  or  25  feet  of  the  course  last  laid,  to  prevent  the 
tipping  of  the  blocks  out  of  the  vertical  position. 

831.  FILLING  THE  JOINTS.  After  the  blocks  have  been 
rammed,  the  joints  are  swept  full  of  pebbles.  For  ordinary  stone 
blocks,  it  is  usually  specified  that  the  pebbles  shall  pass  a  sieve 
having  a  f-inch  mesh  and  be  retained  by  a  |-inch  mesh.  If  the 
pebbles  are  too  small,  they  will  not  permit  the  tar  or  cement  grout, 
with  which  the  joints  are  to  be  filled,  to  flow  freely  to  the  bottom 
of  the  joint.     After  the  joints  have  been  filled  with  these  pebbles, 


Fig.  141.— Stone-block 
Rammer. 


544  STONE-BLOCK    PAVEMENT.  [CHAP.   XVI. 

they  are  tamped  with  a  bar  having  a  chisel-shaped  end.     The  joints 
are  then  again  swept  full  of  pebbles  and  again  tamped. 

832  Three  methods  are  in  more  or  less  common  use  for  com- 
pleting the  filling  of  the  joints. 

1.  The  filling  of  the  joints  is  completed  by  spreading  fine  sand 
over  the  pavement  to  a  depth  of  J  to  1  inch,  and  allowing  traffic  to 
work  it  into  the  joints.  Until  recently  this  was  the  only  method 
employed,  and  even  yet  it  is  by  far  the  most  common.  When 
filled  in  this  way,  the  joints  are  not  impervious;  and  the  filling 
does  not  aid  much  in  keeping  the  blocks  in  position. 

2.  Recently  it  has  become  the  custom  with  the  better  class  of 
stone-block  paving  to  complete  the  filling  of  the  joints  by  pouring 
hot  tar,  or  a  mixture  of  tar  and  asphalt,  over  the  pebbles.  The  tar 
is  applied  in  substantially  the  same  way  as  in  the  case  of  brick 
pavements — see  §  775.  The  pebbles  should  be  perfectly  dry,  for 
an  almost  inappreciable  amount  of  water  will  cause  the  tar  to  foam 
and  will  prevent  it  from  adhering  to  the  pebbles  and  from  forming 
a  solid  joint.  It  may  be  necessary  to  dry  the  pebbles  artificially. 
The  tar  must  not  be  applied  when  the  pebbles  are  very  cold.  The 
joints  should  be  entirely  filled  with  the  tar,  to  secure  which  it  is 
usually  necessary  to  pour  the  joints  twice.  To  keep  the  con- 
tractor from  having  a  financial  interest  in  not  filling  the  joints 
entirely  full,  it  is  sometimes  specified  that  there  shall  be  brought 
upon  the  ground  not  less  than  a  stated  number  of  gallons  of  paving 
cement  for  each  square  yard  of  pavement,  whatever  remains  after 
the  completion  of  the  work  being  the  property  of  the  city. 

The  quantity  of  tar  required  to  fill  the  joints  varies  from  1  to 
3^  gallons  per  square  yard,  according  to  the  width  of  the  joints, 
which  varies  with  the  quality  of  the  stone  and  the  workmanship. 

The  tar  in  the  joints  makes  the  pavement  impervious,  and 
therefore  more  sanitary.  The  tar  also  assists  in  keeping  the  blocks 
in  position,  and  therefore  adds  to  the  durability  and  smoothness 
of  the  pavement. 

3.  In  a  comparatively  few  instances,  the  joints  have  been 
filled  with  Portland-cement  grout,  which  should  be  mixed  and 
applied  as  described  for  brick  pavement— see  §  777.  The  hy- 
draulic-cement grout  makes  the  joint  impervious,  holds  the  blocks 
firmly  in  position,  prevents  the  edges  from  chipping  and  the  top 


ART.   2.]  CONSTRUCTION.  545 


face  from  wearing  round,  and  adds  materially  to  the  smoothness 
and  durability  of  the  pavement. 

833.  MAXIMUM  GRADE.  Stone-block  pavements  are  freely 
employed  upon  grades  up  to  10  per  cent,  and  if  the  stone  is  a  quality 
that  does  not  wear  smooth,  they  may  be  used  upon  grades  up  to 
15  per  cent.* 

It  has  been  recommended  that  on  steep  grades  to  afford  a  good 
foothold  for  the  horses,  (1)  the  edges  of  the  blocks  be  chamfered, 
(2)  that  the  joints  be  comparatively  wTide,  and  (3)  that  the  joints 
be  filled  to  within  about  an  inch  of  the  top  with  cement  mortar. 
It  is  not  known  that  this  expedient  has  ever  been  employed;  but 
the  probabilities  are  that  wide  joints  would  be  equally  as  effective 
without  chamfering  the  blocks,  since  the  edges  spall  off  soon  when 
the  joints  are  wide  and  are  filled  with  either  gravel  or  tar.  Further, 
the  accumulation  of  dirt  in  the  wide  joints  would  probably  largely 
neutralize    their    effect.     -Fig.    142  shows   another    method  that 


Fig.  142.— Stone-block  Pavement  on  Steep  Grade. 

has  been  proposed,  but  it  is  not  known  that  it  has  ever  been 
tried. 

834.  MERITS  AND  DEFECTS.  The  only  merit  claimed  for 
stone-block,  particularly  granite-block,  pavement  is  durability. 
The  material  of  the  blocks  does  not  decay  or  wear  entirely  out; 
but  the  blocks  wear  rounding  and  slick  on  top,  and  get  displaced, 
so  that  the  pavement  becomes  excessively  rough,  noisy,  and  slip- 
pery. Even  the  best  stone-block  pavement  is  rough,  noisy,  and 
difficult  to  keep  clean. 

835.  COST.  The  price  of  stone  paving  blocks  varies  with  their 
size  and  the  quality  of  the  stone.  According  to  the  U.  S.  Eleventh 
Census,  the  average  price  of  granite  blocks  at  the  quarry  varies 


See  §  479. 


546 


STONE- BLOCK    PAVEMENT. 


[CHAP.   XVI. 


in  the  different  states  from  $32.32  to  $78.67,  although  the  range 
is  usually  between  $40  and  $60;  the  average  price  per  thousand 
for  the  entire  country  is  $48.17.  Table  54  gives  the  cost  of 
various  sized  granite  blocks  at  Quincy,  Mass. 

TABLE  54 
Cost  of  Granite  Paving-blocks  f.  o.  b.  Quincy,  Mass 


Ref. 

Dimensions  in  Inches. 

Number  per 
Sq.  Yd. 

No. 

Width. 

Length. 

Depth. 

Thousand. 

1 
2 
3 

4 

4*-5 
4£-5 
4£-5 
4*-5 

10-14 
10-14 

7-  8 
6-  8 

6-8 

6 
6-8 

6 

23 
23 
35 
35 

$50.00 
47.50 
40.00 
35.00 

836.  The  average  cost  to  the  contractor  of  laying  specially 
dressed  granite  blocks  (3 J  to  4  inches  wide,  8  to  10  inches  long,  5 
inches  deep,  of  which  28  to  31  lay  a  square  yard)  at  Chicago  in 
1902  was  about  as  follows : 

TTrw,  Cost  per 

1TEMS-  Sq.  Yd. 

Concrete,  6  inches :  materials  and  labor * $0 .  55 

Sand  cushion,  2  inches:  material  at  $2.00  per  sq.  yd 10 

labor  spreading 02 

Blocks :  cost  f .  o.  b.  Chicago 2.15 

hauling  to  street 10 

carrying  to  paver 03 

laying  and  ramming 13 

Filling  joints,  paving  gravel  at  $2.00  per  cu.  yd 11 

labor  spreading 03 

tar  at  9  cents  per  gallon 09 

labor  applying C6 

Total  cost  to  contractor  exclusive  of  tools  and  administration $3 .37 

Ordinary  granite  blocks  cost  25  to  30  cents  per  square  yard 
less  than  the  special  dressed  blocks  above,  and  the  cost  of  laying 
is  8  cents  per  square  yard  less,  and  the  total  of  the  other  items 
is  substantially  as  above,  thus  making  the  total  cost  of  the  ordinary 
granite-block  pavement  on  concrete  foundation  about  $3.00  per 
square  yard. 

837.  In  New  York  city  the  cost  of  ordinary  granite-block 
pavement  is  as  follows: 


AKT.   2.]  CONSTRUCTION".  547 

T  Cost  per 

Items.  gj  Yd 

Concrete,  6  inches:  materials  and  labor $0.55 

Sand  cushion,  2  inches:  material  at  $1.00  per  cu.  yd 05 

labor  spreading 02 

Blocks:  22\  at  5  cents  on  street 1 .24 

labor  laying 12 

Joint  filling:  3^  gallons  of  tar  at  7  cents 24 

labor  applying 03 

paving  gravel,  1 J  cu.  ft .09 

Total  cost  to  contractor  exclusive  of  administration,  tnob,  etc.  . -     $2.34 

838.  The  cost  of  Medina  sandstone  paving  at  Rochester,  N.  Y., 
in  1902  was  as  follows :  * 

t^wc  Cost  per 

Items-  Sq.  Yd. 

Concrete,  6  inches:  materials  and  labor $0 .50 

Sand  cushion,  2  inches:  at  $1.08  per  cu.  yd.  in  place 0G 

Blocks,  6  inches  deep:  cost  f.  o.  b.  quarry 1 .  15 

freight  to  Rochester 07 

loading  and  unloading 10 

hauling  1  mile 05 

distributing  and  sorting 03 

laying 06 

Filling  joints:  0.02  cu.  yd.  sand  at  $1.00 02 

1^  gallons  of  tar  at  10  cents 15 

labor  applying 06 

Superintendence:  foreman  at  40  cents  per  hour  for  30  sq.  yds 013 

2  water  and  errand  boys 007 

Total  cost  to  contractor  exclusive  of  administration,  tools,  etc.  . .   $2.40 

839.  In  Liverpool,  England,  the  cost  of  a  pavement  of  granite 
blocks  3  inches  wide,  5  to  7  inches  long,  and  1\  inches  deep,  with 

tar-filled  joints,  is  as  follows:  f 

Ttfmr  Cost  per 

lTEMS-  Sq.  Yd. 

0 .  31    ton  granite  "  sets,"  7\  inches  deep,  at  $6 .  72,  including  cartage,  $2 .  08 

0.064    "    gravel  for  bedding,                       "     1.56,        "              "  .10 

0.015    "    coal-tar  pitch,                               "     7.20,        "              "  .105 

0.6      gallon  dead  or  creosote  oil,                 "     0.30,        "              a  .02 

0.002  ton  coke  for  heating  tar,                     "     2.88,        "              "  .005 

0.018    "    shingle,  dried  and  riddled,           "     1.68,        "              "  .03 

Labor 17 

Total,  exclusive  of  administration,  tools,  etc $2 .  51 

*  Engineering  News,  Vol.  48,  p.  70. 

t  Proc.  Inst,  of  Civil  Engineers,  Vol.  58,  p.  1.] 


548  STONE-BLOCK    PAVEMENT.  [CHAP.    XVI. 

If  the  joints  are  filled  with  gravel  only,  the  cost  is  as  follows: 

Ttfm*  Cost  per- 

1TEMS'  Sq.  Yd. 

0.31    ton  granite  "sets,"  at  $6 .  72,  including  cartage,  $2 .  08 

0.096    "    gravel  for  bedding,  1  inch  thick,  "     1.56,        "  "  .18 

0.02      "        "       "    joints,  w     1.44,        "  "  .05 

Labor 10 


Total,  exclusive  of  administration,  tools,  etc $2.41 


CHAPTER  XVII. 
WOOD-BLOCK  PAVEMENTS. 

840.  Wood  appears  to  have  been  employed  as  a  paving  material 
first  in  Russia,  where,  though  rudely  fashioned,  it  has  been  used 
for  some  hundreds  of  years.  Wood  pavements  were  first  laid  in 
New  York  city  in  1835-36,  and  in  London  in  1839.  Wood-block 
pavements  are  constructed  less  frequently  in  this  country  now  than 
formerly,  the  decrease  being  probably  due  in  part  to  the  intro- 
duction of  brick  pavements.  Within  the  past  two  years,  however, 
wood  pavements  seem  to  be  growing  somewhat  in  favor. 

Art.  1.    The  Wood. 

841.  VARIETIES.  Both  the  hard  and  the  soft  varieties  of  wood 
have  been  employed  for  making  paving  blocks.  The  hard  woods 
are  used  without  preservative  treatment,  and  the  soft  ones  are  used 
both  with  and  without  preserving  (see  §  844).  In  the  United 
States,  cedar  and  cypress,  on  account  of  their  abundance,  cheap- 
ness, and  durability  against  decay,  are  more  generally  employed. 
In  Europe  nearly  all  varieties  of  the  pine  species  have  been  tried, 
as  well  as  oak,  ash,  elm,  and  gum ;  but  Baltic  fir,  Indian  teak,  and 
Swedish  deal  seem  to  be  the  favorites.  Within  the  past  few  years, 
two  Australian  hard  woods,  jarrah  and  karri,  have  been  intro- 
duced in  London  for  paving  purposes,  and  have  been  favorably 
received. 

None  of  the  woods  employed  for  making  paving  blocks  need  a 
description,  except  perhaps  the  Australian  hard  woods,  jarrah  and 
karri. 

842.  Jarrah  and  Karri.  Jarrah  is  short  grained  and  free  split- 
ting, and  breaks  with  a  clean  fracture  and  burns  with  a  black  ash. 
In  color  it  looks  nearly  like  cherry.  When  seasoned,  it  has  a  specific 
gravity  of  1.01  and  absorbs  about  10  per  cent  of  water  when  im- 

549 


550  WOOD-BLOCK    PAVEMENTS.  [CHAP.  XVII. 

mersed  48  hours.*     Its  transverse  and  crushing  strength  is  about 
the  same  as  that  of  English  oak  and  Indian  teak. 

Karri  is  interlocked  in  the  grain  and  is  difficult  to  split;  it 
splinters  in  breaking  and  burns  with  a  white  ash.  It  is  a  little 
lighter  colored  than  cherry.  When  seasoned;  it  has  a  specific 
gravity  of  1.12,  and  absorbs  about  7  per  cent  of  water  when 
immersed  48  hours.  Its  transverse  strength  is  a  little  greater 
than  that  of  English  oak  or  Indian  deal,  and  its  crushing  strength 
is  considerably  greater. 

For  street  paving,  there  is  little  difference  between  jarrah  and 
karri,  although  for  exceptionally  heavy  traffic  karri  shows  slightly 
less  wear.  Karri  shrinks  less  than  jarrah.  Both  timbers  are  very 
plentiful  in  Western  Australia,  the  trees  growing  with  large,  long^ 
straight  bodies  without  limbs.  Jarrah  and  karri  are  preferred 
in  some  vestries  of  London  to  any  other  form  of  wood  paving- 
blocks. 

843.  QUALITY  OF  WOOD.  Whatever  the  variety  of  the  wood, 
it  should  be  sound,  close-grained,  uniform  in  quality,  free  from  sap 
and  knots  and  from  the  blue  tinge  which  is  a  sign  of  incipient 
decay. 

844.  Preservation  of  Wood.  A  wood  pavement  fails 
through  wear  and  decay.  A  number  of  methods  have  been  in- 
vented for  increasing  the  durability  of  timber  against  decay;  and 
although  these  methods  have  been  employed  to  a  considerable 
extent  for  preserving  piles,  railroad  ties,  and  bridge  timbers,  they 
have  been  used  only  to  a  limited  degree  in  this  country  for  pre- 
serving paving  blocks. 

Experiments  in  wood  preserving  date  back  some  centuries, 
and  the  list  of  substances  experimented  with  seems  nearly  endless ; 
but  there  are  only  a  few  antiseptics  that  have  stood  the  test  of  time 
or  have  been  worked  commercially.  According  to  the  antiseptic 
employed,  the  principal  methods  of  preserving  timber  may  be 
grouped  into  four  classes: 

1.  Kyanizing — use  of  corrosive  sublimate. 

2.  Burnettizing — the  use  of  chloride  of  zinc. 

3.  Boucherizing — the  use  of  sulphate  of  copper. 

4.  Bethellizing — the  use  of  creosote  oil. 


*  Most  soft  woods  will  absorb  20  to  25  per  cent. 


ART.   1.]  THE   WOOD.  551 

The  only  one  of  these  methods  that  is  suitable  for  preserving  wood 
paving-blocks  is  the  last,  since  the  mineral  salts  used  by  the  others 
wash  out.  There  are  various  methods  of  using  the  above  anti- 
septics, as  applying  externally  with  a  brush,  steeping  or  immers- 
ing, exposing  to  vapors,  injecting  in  closed  tanks  under  pressure, 
etc.;  but  the  only  method  employed  for  paving  blocks  is  that  of 
injecting  the  creosote  under  pressure. 

845.  Creosoting.  This  process  consists  of  impregnating  the 
wood  with  the  oil  of  tar,  called  creosote,  from  which  the  am- 
monia has  been  expelled.  The  effect  is  to  coagulate  the  albumen 
and  thereby  to  prevent  its  decomposition,  and  also  to  fill  the  pores 
of  the  wood  with  a  bituminous  substance  which  excludes  both 
air  and  moisture,  and  which  is  noxious  to  the  lower  forms  of  animal 
and  vegetable  life. 

The  timber  to  be  preserved  should  be  thoroughly  seasoned.  It 
is  then  put  into  a  closed  cylinder,  and  the  air  is  exhausted.  Hot 
creosote  is  allowed  to  flow  in;  and  when  the  cylinder  is  full,  a 
force-pump  is  applied  and  the  pressure  raised  to  150  or  200  pounds 
per  square  inch.  The  wood  remains  under  pressure  until  it  has 
absorbed  the  requisite  quantity  of  oil,  as  indicated  by  a  gage  on 
the  tank.  For  protection  against  decay,  it  is  necessary  to  inject 
from  8  to  12  pounds  per  cubic  foot.  The  woods  which  are  best 
adapted  to  this  treatment  are  those  which  are  most  absorbent, 
and  therefore  the  easiest  and  quickest  destroyed,  as  the  gums 
and  cottonwoods.  Cypress,  cedar,  pine,  and  porous  oaks  are 
absorbent  and  can  be  successfully  treated.  Creosoting  is  quite 
expensive  owing  to  the  cost  of  the  creosote  and  to  the  expense  of 
injecting  it,  the  cost  being  from  $12  to  $18  per  1,000  feet,  board 
measure. 

Creosoted  paving  blocks  have  been  laid  during  the  last  five  or 
six  years  in  several  Western  and  Southern  cities,  notably  Indian- 
apolis, Terre  Haute,  Galveston,  and  New  Orleans.  In  Indian- 
apolis the  experience  of  six  years'  service  has  been  highly  satis- 
factory, the  pavement  showing  increased  popularity  over  all  other 
forms  of  roadway.  Creosoted  wood  blocks  are  exclusively  used 
in  Paris  and  much  used  in  London. 

846.  Creosote  is  a  good  preservative,  but  evaporates  and  is 
washed  out  by  the  rains.      To  remedy  these  defects,  two  modifi- 


552  WOOD-BLOCK   PAVEMENTS.  [CHAP.   XVII. 

cations  of  the  above  process  have  been  recently  introduced.     One  is 
called  the  kreodone-creosote  and  the  other  the  creo-resinate  process. 

847.  Kreodone-Creosote  Process.  This  consists  in  impregnating 
the  seasoned  blocks  under  pressure  with  an  oil  derived  from  creo- 
sote oil  which  possesses  the  original  preservative  properties  with 
a  longer  endurance,  and  which  also  has  the  effect  of  forming  a 
varnish-like  film  or  coating  on  the  outer  surface  of  the  wood,  thus 
protecting  it  from  the  elements.  The  blocks  are  sterilized  by 
subjecting  them  to  dry  heat  of  240°  F.  for  eight  hours.  The 
kreodone  oil  is  then  forced  into  the  fibers  of  the  wood,  under  a 
pressure  of  70  pounds  per  square  inch,  maintained  for  two  or  three 
hours,  until  12  pounds  have  been  absorbed  by  each  cubic  foot  of 
the  wood.  The  advantage  claimed  for  this  process  over  ordinary 
creosoting  is  that  the  kreodone  creosote  is  not  as  easily  washed 
out  or  as  easily  volatilized  as  creosote. 

Samples  of  this  pavement  were  laid  in  1901  in  Chicago  on 
Michigan  Avenue  in  front  of  the  Auditorium  Hotel,  and  in  Indian- 
apolis on  North  Delaware  Street. 

848.  Creo-Resinate  Process.  The  special  feature  of  this  process 
is  the  mixing  of  dead  oil  of  coal  tar  (creosote)  with  melted  resin 
and  formaldehyde.  The  resin  is  used  to  render  the  wood  water- 
proof, and  to  prevent  the  washing  away  of  the  mixture;  and  the 
formaldehyde  is  used  to  strengthen  the  antiseptic  nature  of  the 
compound.  The  creo-resinate  mixture  is  applied  hot  under  press- 
ure, and  is  followed,  in  another  cylinder,  by  the  injection  of  hot 
milk-of-lime  under  pressure,  in  order  to  fix  and  set  the  creosote. 

It  is  claimed  that  this  process  increases  the  density  of  the  wood 
and  also  its  resistance  to  impact  and  abrasion  over  either  untreated 
or  creosoted  wood.*  It  is  further  claimed  that  the  more  porous 
blocks  take  up  more  of  the  creo-resinate  mixture  than  the  denser 
ones,  and  consequently  increase  in  density  and  strength  to  a 
greater  degree,  the  process  thus  making  the  blocks  more  uniform 
in  quality.     This  is  probably  true,  but  only  in  a  slight  degree. 

Pavements  treated  by  this  process  have  been  laid  within  the 
past  two  years  in  Boston  f  and  Springfield,  Mass.,  and  in  Balti- 
more, Md.,  and  seem  to  be  giving  satisfaction. 

*  Trans.  Amer.  Soc.  Civil  Eng'rs,  Vol.  44,  p.  181-193. 

f  Proc.  Amer,  Soc.  of  Municipal  Improvements,  1901,  p.  212-17. 


AKT.  2.]  THE   CONSTRUCTION.  553 

849„  Value  of  Preserved  Wood  for  Payments.  If  the  pave- 
ment on  a  particular  street  is  worn  out  by  traffic  before  the  wood 
has  time  to  decay  materially,  then  except  in  so  far  as  the  treatment 
adds  to  its  strength,  the  preservation  of  the  wood  will  be  ineffective ; 
but  if  the  deterioration  due  to  decay  is  considerable,  then  the  pre- 
servative treatment  may  add  to  the  life  of  the  pavement.  There 
is  considerable  difference  of  opinion  as  to  the  relative  value  of 
treated  and  untreated  wood  for  paving  purposes.  The  relative 
merits  of  the  two  vary  with  the  climate,  the  amount  of  traffic,  the 
kind  of  wood,  and  the  cost  of  treatment;  and  an  economic  solution 
of  this  problem  is  dependent  upon  the  cost  of  both  forms  of  wood- 
block pavement  in  comparison  with  the  various  other  kinds  of 
pavements.  Some  vestries  in  London,  where  there  are  large  areas 
of  both  treated  and  untreated  wood-block  pavements,  favor  pre- 
served soft-wood  blocks  and  some  unpreserved  hard-wood  blocks- 
all  apparently  under  substantially  the  same  conditions.  Paris, 
which  also  has  large  areas  of  wood  pavements,  seems  to  favor 
blocks  impregnated  with  8  to  10  pounds  of  creosote  per  cubic  foot. 

850.  In  this  country  and  in  London,  there  has  been  not  a  little 
discussion  concerning  the  relative  merits  of  untreated  Australian 
hard  wood  and  treated  soft  wood  as  a  paving  material  for  the 
streets  of  London.*  The  engineers  of  some  vestries  prefer  the 
one  and  some  the  other,  but  a  significant  fact  is  that  the  loans 
made  by  the  London  County  Council  (the  central  governing  board) 
to  the  vestries  for  paving  purposes  are  payable  in  the  case  of  soft- 
wood paving  in  5  years,  and  in  the  case  of  Australian  hard-wood 
in  12  years. 

Art.  2.    The  Construction. 

851.  Much  ingenuity  and  inventive  genius  has  been  exercised 
to  discover  some  odd  or  novel  way  to  cut  and  lay  the  blocks, 
twenty -five  or  thirty  patents  having  been  issued  in  this  country 
during  the  first  twenty-five  or  thirty  years  of  the  history  of  wood- 
block pavements.  More  attention  appears  to  have  been  given 
to  the  form  of  the  block  than  to  the  strength  and  durability  of  the 
wood.     All  of  these  complicated  forms  have  been  forgotten,  and 

*  Engineering  Xews,  Vol.  43,  p.  353  ;  Vol.  44,  p.  126-27,  409  ;  Vol.  46,  p.  107. 


554 


WOOD-BLOCK   PAVEMENTS. 


[CHAP.  XVII. 


now  the  only  ones  used  are  cylinders,  and  parallel opipedons,  the 
former  frequently  being  called  round  blocks  and  the  latter  rectan- 
gular or  square  blocks;.    The  fiber  of  the  wood  is  always  set  vertical. 


A.   ROUND   WOOD-BLOCK   PAVEMENT. 

852.  This  pavement  consists  of  short  sections  of  cylindrical 
blocks  set  with  the  grain  vertical,  side  by  side  as  close  together 
as  possible.  Fig.  143  shows  a  cross  section  and  a  perspective  of 
this  form  of  pavement. 


Fig.  143.— Round  Wood-block  Pavement. 

853.  FOUNDATION.  The  blocks  are  sometimes  set  airectly 
upon  the  native  soil,  after  it  has  been  properly  shaped  and  rolled; 
and  sometimes  upon  a  layer  of  sand. 

The  usual  and  best  foundation  is  constructed  by  spreading  a 
layer  of  coarse  sand,  about  3  inches  thick,  upon  the  prepared  sub- 
grade.  Boards,  1  inch  thick  and  8  to  12  inches  wide,  are  then  laid 
lengthwise  of  the  street  from  curb  to  curb,  usually  8  feet  apart,  and 
are  carefully  bedded  in  the  sand  to  the  true  cross  section  of  the  road- 
way. These  boards  are  to  support  the  ends  of  the  planks  which 
form  the  foundation  for  the  blocks.  After  the  stringers  are  in 
place  and  well  tamped,  a  straight  edge  or  scraper  reaching  from 
one  stringer  to  another  is  drawn  from  one  side  of  the  street  to  the 
other,  thus  leveling  the  sand  flush  with  the  top  of  the  stringers. 


ART.  2.]  THE   CONSTRUCTION".  555 

If  the  sand  is  damp,  it  should  be  compacted  by  ramming.  It  is 
well  to  leave  the  sand  a  little  higher  than  the  stringers,  in  order 
to  be  sure  that  the  foundation  boards  have  a  perfect  support  upon 
the  sand  throughout  their  entire  surface.  Sand  can  easily  be  fitted 
to  the  true  surface,  while  it  would  be  almost  impossible  to  grade 
clay  or  loam  as  evenly.  The  sand  also  assists  in  draining  away 
any  water  which  percolates  through  the  paving. 

On  the  stringers  and  the  sand,  the  foundation  planks  are 
laid  close  together,  across  the  street,  the  ends  abutting  on  the 
stringers.  These  planks  should  be  a  fair  quality  of  well  seasoned 
lumber;  and  are  usually  1  inch  thick,  but  occasionally  2  inches 
thick,  and  sometimes  are  coated  with  hot  tar.  If  the  board  is  well 
seasoned  and  perfectly  dry,  the  coal  tar  will  increase  the  durability 
of  the  material;  but  if  there  is  any  sap  or  any  moisture  in  the  lum- 
ber, the  coal  tar  would  effectually  seal  it  up  and  hasten  dry  rot 
on  the  inside. 

854.  Round  blocks  are  occasionally  laid  upon  a  concrete 
foundation,  but  such  construction  is  not  advisable  under  ordinary 
conditions.  Round  wood-block  pavements  are  justifiable  only 
where  low  first  cost  is  absolutely  necessary,  in  which  case  a 
concrete  foundation  is  inappropriate. 

855.  THE  BLOCKS.  These  are  prepared  by  sawing  sections  6 
inches  long  from  poles  4  to  8  inches  in  diameter.  The  wood  is 
usually  red  or  white  cedar,*  although  tamarac,  yellow  pine,  and 
cypress  are  sometimes  used.  Cedar  is  more  durable  in  wet  ground 
than  any  other  wood.  Generally  the  bark  is  removed  from  the 
poles  before  cutting  them  into  paving  blocks;  but  about  1880 
there  was  invented  a  machine  for  removing  also  the  sap.  Machine- 
made  sapless  blocks  are  truly  circular  and  the  same  size  at  both 
ends,  and  fit  together  much  more  closely  than  rough  irregular 
undressed  blocks,  and  hence  make  a  smoother  pavement.  Ordi- 
nary cedar  blocks  have  from  25  to  35  per  cent  of  sap,  and  as  the 
sap  is  less  durable  against  decay  than  heart  wTood  and  has  less 
strength  to  resist  crushing  under  traffic,  the  sapless  blocks  do  not 
wear  round  on  the  top  face  as  rapidly  as  the  undressed  blocks. 
Sapless  blocks  were  laid  to  a  considerable  extent  in  Saginaw  and 

*  The  timber  known  as  -white  cedar  in  the  North  is  called  juniper  in  the  South. 


556  WOOD-BLOCK    PAVEMENTS.  [CHAP.   XVII. 

other  cities  in  Michigan  from  1880  to  1890;  but  owing  to  the  in- 
creasing price  of  timber,  and  to  the  introduction  of  brick  pave- 
ments, and  to  the  decrease  in  the  cost  of  asphalt  pavements,  they 
are  not  now  laid.  At  the  factory  in  East  Saginaw,  machine-made 
sapless  cedar  blocks  cost  about  10  cents  per  square  yard  more  than 
undressed  blocks. 

856.  LAYING  THE  BLOCKS.  The  blocks  are  placed  on  end 
close  together  upon  the  plank  foundation,  and  are  packed  in  such 
a  way  that  the  spaces  between  the  adjoining  blocks  have  only  three 
sides  rather  than  four  or  more.  The  closest  packing  gives  trian- 
gular spaces.  Projecting  knots  or  bunches  on  the  side  of  the  block 
should  be  cut  off,  so  that  the  blocks  may  stand  close  together. 
Occasionally  it  is  necessary  to  split  off  a  piece  of  a  block  in  order 
to  make  it  fit  up  closely  against  the  adjoining  ones;  but  no  portion 
of  a  split  block  less  than  3  inches  in  diameter  should  be  used,  and 
the  edges  of  split  blocks  should  be  cut  away  so  as  to  be  not  less  than 
1  inch  thick  at  the  thinnest  part.  Two  split  surfaces  should 
not  be  laid  in  contact  with  each  other.  In  paving  against  the 
curb,  each  alternate  block  should  be  split  in  halves,  and  the  straight 
side  be  placed  against  the  curb.  In  no  case  should  blocks  having 
the  same  diameter  be  set  in  a  row  across  the  street,  but  the  various 
sizes  should  be  intermingled  with  each  other. 

After  the  blocks  are  in  place,  the  spaces  between  them  are 
filled  with  pea  gravel.  Sometimes  the  gravel  is  simply  swept  into 
the  joints,  a  surplus  being  left  upon  the  surface  to  be  worked 
in  further  by  traffic ;  and  sometimes  the  gravel  is  tamped  into  place ; 
and  in  a  comparatively  few  cases,  tar  or  paving  cement  is  poured 
upon  the  pebbles  in  the  joints.  If  the  gravel  is  tamped  into  place, 
there  should  be  two  men  tamping  for  each  one  laying  blocks.  The 
tar  makes  the  joints  impervious  and  also  assists  in  preventing  the 
blocks  from  being  displaced  by  traffic  or  from  being  floated  away 
when  the  pavement  is  flooded.  If  paving  cement  is  used,  the 
blocks  and  the  gravel  should  be  perfectly  dry.  The  hot  tar  in 
coming  in  contact  with  moisture  forms  steam  which  blows  the  tar 
full  of  bubbles  and  destroys  its  cementing  power.  The  entire 
surface  of  the  pavement  is  finally  covered  with  about  1  inch  of  fine 
roofing  gravel,  which  should  be  heated  in  order  that  it  may  bed 
itself  into  the  tar. 


ART.   2.] 


THE   CONSTRUCTION. 


557 


857.  COST.  In  Chicago  in  1900,  a  6-inch  cedar-block  pave- 
ment on  2-inch  hemlock  planks  which  rest  on  1-inch  pine  stringers 
8  feet  apart,  with  2  inches  of  sand  foundation,  cost  from  $1.04  to 
$1.20  per  square  yard,  the  average  being  about  $1.10.  In  Michi- 
gan, Wisconsin,  and  Minnesota,  6-inch  cedar  blocks  on  1-inch 
boards  and  1-inch  stringers  cost  from  60  cents  to  $1.05  per  square 
yard,  the  range  usually  being  from  75  to  95  cents. 

B.      RECTANGULAR   WrOOD- BLOCK   PAVEMENT. 

858.  A  pavement  composed  of  parallelopipedons,  or  "  rectangu- 
lar blocks,"  was  patented  by  Nicholson  in  1848 ;  and  for  a  number 
of  years  thereafter  this  form  was  in  this  country  generally  called 
Nicholson  pavement,  and  even  yet  the  term  is  often  used.  Fig. 
144  shows  the  usual  construction.      This  form  of  pavement  is 


Fig.  144.— Rectangular  Wood-block  Pavement. 


now  used  in  this  country  only  to  a  limited  extent.  It  is  the 
only  form  of  wood  pavement  in  Europe,  and  is  used  quite  exten- 
sively in  London  and  in  Paris. 

859.  FOUNDATION.  Rectangular  blocks  may  be  laid  upon  a 
foundation  of  sand  or  upon  plank;  but  in  the  best  practice  are 
laid  upon  a  layer  of  well-consolidated  broken  stone  or  upon  a  bed 
of  concrete.     Concrete  is  used  exclusively  in  both  London  and  Paris. 


558  WOOD-BLOCK    PAVEMENTS.  [CHAP.   XVII. 

In  this  country  a  cushion  coat  of  sand  is  interposed  between 
the  concrete  and  the  blocks;  but  in  London  and  in  Paris  the  con- 
crete, after  having  been  laid  quite  smooth  and  level,  is  floated,— 
i.  e.,  the  surface  is  coated  with  a  thin  layer  of  lean  Portland-cement 
mortar  making  a  bed  for  the  blocks  almost  as  smooth  as  the  plastered 
walls  of  a  house. 

860.  THE  BLOCKS.  The  blocks  should  be  cut  from  sound 
timber  without  wind  shakes,  knots,  or  rotten  spots,  and  should 
be  free  from  sap  wood.  The  faces  should  be  flat,  and  the  corners 
square.  The  top  and  the  bottom  should  be  truly  parallel,  and  at 
right  angles  to  the  sides. 

861.  Apparently  the  best  dimensions  for  the  blocks  are:  width 
3  inches,  depth  4  to  6  inches,  length  9  inches.  Formeny  a  depth 
of  6  inches  was  almost  always  employed,  but  it  was  found  that 
after  the  blocks  had  worn  down  2  or  3  inches  the  pavement  was 
so  rough  and  uneven  as  to  require  re-laying;  and  now  the  blocks 
are  only  4  or  5  inches  deep,  even  under  the  heaviest  traffic.  If 
the  pavements  are  re-laid  before  the  surface  becomes  very  rough, 
an  original  depth  of  4  inches  is  enough.  This  is  the  depth  now 
generally  preferred  in  London,  a  city  having  not  only  many  wood 
pavements  but  also  the  finest  wood  pavements  in  the  world. 

Part  of  the  excellence  of  the  London  wood  pavements  is  due 
to  the  uniformity  of  the  blocks,  the  engineers  of  some  of  the  Ves- 
tries not  permitting  a  greater  variation  either  way  from  the  speci- 
fied width  and  length  than  TV  inch,  and  not  permitting  any  meas- 
urable variation  in  the  depth.  It  is  also  specified  that  the  corners 
of  the  blocks  shall  be  exactly  square. 

862.  PLACING  THE  BLOCKS.  The  blocks  are  set  with  the  fiber 
vertical  and  the  long  dimension  crosswise  of  the  street.  In  Lon- 
don the  more  discriminating  engineers  specify  that  the  lap  shall 
be  one  third  of  the  length  of  the  block,  a  lap  which  diminishes  the 
tendency  for  ruts  to  form  in  line  with  the  end  joints. 

Formerly  it  was  believed  that  the  side  joints  should  be  left  open 
to  afford  a  foot  hold  for  horses,  the  first  rectangular  block  pave- 
ments in  this  country  being  laid  with  a  f-inc1:  strip  between  the 
rows  of  blocks.  Wide  joints  hasten  the  destruction  of  the  wood 
by  permitting  the  fibers  to  spread  under  traffic,  which  also  causes 
the  surface  of  the  pavement  to  wear  in  small  ridges,  giving  to  it  a 


ART.   2.] 


THE    CONSTRUCTION. 


559 


corduroy  effect.  The  best  practice  seems  to  be  to  lay  the  blocks 
on  level  streets  with  joints  as  thin  as  possible;  while  on  grades  of 
3  per  cent  or  over,  some  engineers  advocate  a  |-inch  joint  made  as 
follows:  Remove  from  the  top  of  one  side  of  each  block  a  strip 
J-inch  thick  and  1  J-inches  deep  for  the  length  of  the  block.  When 
these  blocks  are  laid  as  above  described,  and  driven  closely  to- 
gether, there  is  a  quarter  of  an  inch  opening,  or  joint,  extending 
clear  across  the  street  in  each  course  of  block,  J  inch  wide,  and  1J 
inches  deep.  These  joints  are  filled  with  Portland  cement 
mortar.     Fig.  145  shows  a  section  of  pavement  having  this  form 


Fig.  145. — Rectangular  Wood-block  Pavement  with  Wide  Joints. 

of  joint.      Such  a   pavement   was   recently  laid   in   Boston  on 
Boylston  Street. 

863.  FILLING  THE  JOINTS.  When  the  blocks  are  laid  close 
together,  the  joints  are  filled  either  (1)  by  sweeping  in  fine  hot  sand 
(§  774),  or  (2)  by  pouring  in  boiling  hot  tar  or  paving  pitch  (§  775), 
or  (3)  by  sweeping  in  neat  Portland  cement  grout  (§  777).  When 
the  blocks  are  laid  with  spaces  between  them,  the  joints  are  filled 
with  a  1  to  1  Portland  cement  grout.  Whatever  the  joint  filler, 
a  light  coat  of  fine  gravel  or  paving  sand  is  strewn  over  the  surface, 
ind  then  the  pavement  is  opened  to  traffic. 

864.  EXPANSION.  All  untreated  wood  blocks  absorb  water  and 
expand  to  a  considerable  extent,  and  treated  blocks  expand  appre- 
ciably.    The  average  expansion  of  creosoted  and  untreated  wood 


560  WOOD-BLOCK    PAVEMENTS.  [CHAP.    XVII. 

blocks  after  immersion  in  water  for  forty-eight  hours  is  about  as 
follows : 

Dimension.  Per  Cent  of  Expansion. 

Untreated.  Creosoted. 

On  length  of  block 0.60  0.10 

"   width  "      "     0.83  0.57 

"    depth   «      "     0.31  0.15 

At  the  above  rates,  the  expansion  in  the  width  of  a  30 -foot  pave- 
ment would  be  2£  inches  for  untreated  blocks  and  practically  jf  inch 
for  creosoted  blocks,  provided  the  blocks  were  fully  saturated; 
but  the  blocks  will  never  be  this  wet,  and  therefore  the  maximum 
expansion  will  be  considerably  less  than  that  stated.  If  either 
treated  or  untreated  blocks  are  laid  in  contact  or  with  a  rigid  filler, 
the  expansion  due  to  absorption  of  water  is  likely  to  disturb  the 
curbs  or  lift  the  blocks  from  the  foundation.  This  expansion  may 
be  provided  for  by  the  same  method  as  that  of  brick  pavements 
due  to  heat  (see  §  786). 

In  London,  expansion  is  provided  for  by  leaving  between  the 
blocks  and  the  curb,  a  space  of  1 J  inches  which  is  filled  either  with 
clay  or  with  clean,  dry  sand,  coated  over  with  a  film  of  Portland 
cement  mortar.  In  Chicago  pine  blocks  laid  fairly  dry,  and  having 
the  joints  filled  with  sand,  do  not  ordinarily  expand  sufficiently 
to  lift  the  blocks  from  the  foundation;  but  oak  blocks  so  laid 
usually  swell  sufficiently  to  heave  the  pavement. 

865.  REPAIRS.  The  only  repairs  required,  aside  from  re-placing 
blocks  taken  up  to  get  at  water  and  gas  pipes,  etc..  is  to  remove 
soft  or  decayed  blocks  and  to  insert  new  ones.  The  hole  caused 
by  a  single  decayed  block  is  speedily  enlarged  by  the  impact  of 
wheels  dropping  into  the  depression.  The  top  face  of  the  new  block 
should  not  be  higher  than  the  general  surface  of  the  pavement  for  a 
high  block  is  fully  as  serious  a  defect  as  a  low  one. 

It  is  frequently  stated  that  the  average  cost  of  repairs  of  wood 
pavements  in  English  and  Continental  cities  is  from  1|  to  3  cents 
per  square  yard  per  annum ,  but  such  data  are  not  very  instruc- 
tive since  nothing  is  known  concerning  the  nature  and  the  amount 
of  the  traffic  per  unit  of  width,  the  details  of  the  construction  of 
the  pavement,  the  climatic  conditions,  the  cause  and  nature  of  the 
repairs,  etc. 


ART.  2.]  THE    CONSTRUCTION.  561 


866.  PERMISSIBLE  GRADES.  Rectangular  wood  blocks  with 
close  joints  are  used  on  grades  up  to  3  or  5  per  cent  without  being 
seriously  slippery.  The  limit  depends  upon  the  climate,  the  cleanli- 
ness of  the  pavement,  and  the  character  of  the  wood  employed. 
In  London  and  Paris,  it  is  customary  to  strew  coarse  sand  and 
small  pebbles  over  the  surface  of  wood  pavements  to  keep  them 
from  becoming  slippery.  The  sand  grains  and  the  pebbles  be- 
come imbedded  in  the  wood,  are  quite  effective  in  preventing  the 
horses  from  slipping,  and  add  somewhat  to  the  durability  of  the 
pavement.  In  London  the  limiting  grade  for  wood  blocks  is 
usually  considered  4  per  cent,  although  Savoy  Street,  the  grade  of 
which  is  8  per  cent,  and  Arundel  Street,  the  grade  of  which  is  7 
per  cent,  are  paved  with  wood.  On  grades  greater  than  3  to  5 
per  cent,  it  is  customary  to  lay  the  blocks  with  open  joints  (§  862). 
Sidney,  New  South  Wales,  has  a  rectangular  block  pavement  upon 
an  8  per  cent  grade,  which  gives  no  serious  trouble.  Duluth, 
Minn.,  uses  round  blocks  on  a  10  per  cent  grade  or  less,  but  on 
steeper  grades  uses  rectangular  blocks  with  f-inch  joints  filled 
with  gravel. 

867.  MERITS  AND  DEFECTS.  The  chief  merit  of  a  rectangular 
block  pavement  is  its  quietness ;  and  its  chief  defects  are  its  slipperi- 
ness,  its  lack  of  durability  if  not  preserved,  and  its  cost  if  treated. 

In  this  country  brick  or  sheet  asphalt  has  taken  the  place 
formerly  occupied  by  wood-block  pavement;  but  in  Europe,  par- 
ticularly in  London  and  Paris,  when  a  quiet  pavement  is  desired, 
the  contest  is  between  broken  stone  on  the  one  hand  and  rock 
asphalt  on  the  other. 

868.  COST.  Oregon  red-cedar  and  southern  yellow-pine  heart- 
wood  blocks,  4"  X  4"  X  9'',  creosoted  with  10  pounds  per  cubic 
foot,  were  laid  in  1899  in  Indianapolis,  Ind.,  at  a  cost  of  $2.10  to 
$2.50  per  square  yard,  including  the  concrete  base  and  a  five-year 
guarantee,  the  joints  being  filled  with  paving  cement  of  nine  parts 
of  coal  tar  to  one  part  of  asphalt,  and  the  surface  being  covered 
with  half -inch  screenings  of  crushed  granite. 

The  5-inch  kreodone-creosoted  blocks  laid  in  1901  in  front  of  the 
Auditorium  Hotel  on  Michigan  Avenue,  Chicago  (§  847),  cost  $1.90 
a  square  yard,  including  a  5-year  guarantee  but  not  including  the 
concrete  base. 


562  WOOD-BLOCK   PAVEMENTS.  [CHAP.  XVII. 

The  4-inch  creo-resinated  wood-block  pavement  laid  in  Boston 
(§  848)  in  1901  cost  from  $3.10  to  $3.50  a  square  yard,  including  a 
6-inch  concrete  foundation  and  a  10-year  guarantee. 

869.  In  London  5-inch  jarrah  blocks  cost  from  £10  to  £11 
($48.40  to  $53.20)  a  thousand,  and  karri  blocks  about  $1.20  a  thou- 
sand less;  and  the  pavement  complete  on  an  old  foundation  costs 
from  $2.50  to  $3.00  per  square  yard.  The  cost  of  a  creosoted- 
deal  pavement  on  an  old  foundation  varies  from  $1.50  to  $2.00 
per  square  yard. 

870.  In  Paris  pine  blocks  of  various  kinds,  impregnated  with 
8  to  10  pounds  of  creosote  oil  per  cubic  foot,  constitute  the  greater 
part  of  the  90  miles  of  wood  pavements,  and  cost,  including  a  6-inch 
concrete  base,  about  $3.10  per  square  yard. 


CHAPTER  XVIII. 
COMPARISONS  OF  PAVEMENTS. 

872.  Pavements  have  been  constructed  of  a  variety  of  materials; 
but  the  forms  discussed  in  the  preceding  chapters — asphalt,  brick, 
stone  block,  and  wood  block — are  the  only  ones  of  importance 
now  constructed,  and  it  is  improbable  that  any  other  paving  ma- 
terial of  value  will  be  introduced.  From  time  to  time  notices 
appear  in  the  general  newspapers  of  the  introduction  of  some  new 
pavement.  Among  the  new  paving  materials  of  which  notices  have 
recently  appeared  are  compressed  hay,  devitrified  glass,  cork,  and 
rubber.  All  such  novelties  are  either  an  attempt  of  an  eccentric 
inventor  to  sell  his  goods  or  a  construction  to  meet  limited  and 
peculiar  conditions.  For  example,  it  has  been  stated  that  rubber 
has  been  tried  as  a  paving  material  in  London;  but  the  facts  are 
that  it  has  been  used  only  to  the  extent  of  300  or  400  square  feet 
in  a  hotel  porte  cochere. 

Macadam  and  gravel  were  considered  in  Part  I  as  materials 
for  surfacing  country  roads,  but  it  will  presently  be  shown  that  they 
are  employed  as  a  covering  material  on  half  or  more  of  the  ' '  paved  " 
streets  of  the  cities  of  the  United  States ;  *  and  therefore  macadam 
and  gravel  roads  must  in  this  chapter  be  considered  as  pavements. 
These  materials  are  entirely  unsuitable  for  streets  having  a  heavy 
traffic,  on  account  of  the  surface  being  speedily  ground  to  powder 
which  makes  dust  and  mud  and  necessitates  frequent  repairs  which 
are  likely  to  hinder  traffic ;  but  they  have  some  very  desirable  quali- 
ties for  purely  residence  streets  and  for  the  main  streets  of  small 


*  In  Table  55,  page  564,  these  two  constitute  45  per  cent,  and  in  Table  56,  page 
565,  59  percent;  but  if  the  smaller  cities  were  included  the  percent  of  gravel  and 
macadam  pavements  would  probably  be  still  larger. 

563 


564 


COMPARISONS    OF    PAVEMENTS.  [CHAP.   XVIII. 


towns,  and  are  eminently  fitted  for  pleasure  drives  in  parks  and 
elsewhere. 

873.  Amount  of  Different  Kinds  of  Pavements.    Table 
55  shows  the  number  of  miles  and  also  the  relative  proportion  of 


TABLE  55. 

Number  of  Miles  and  Relative  Proportion  of  the  Different  Kinds 
of  Pavements  in  One  Hundred  and  Thirty-five  American 
Cities  in  1901.* 


Ref. 
No. 

•      j 

Kind  of  Pavements.                                    Miles. 

Per  Cent. 

1 

Asphalt — sheet  and  block 

2  061 
1  186 

13.6 

2 

Brick 

7.9 

3 

Cobble  Stone 

1034 
2  020 
2  225 
4  615 
1313 
645 

6.8 

4 
5 

Granite  and  Belgian  Blocks 

Gravel 

13.4 
14.7 

6 

Macadam. 

30.6 

7 

Wood 

8.7 

8 

All  others 

4  3 

Total 

15  099                  100.0 

1 

*  Compiled  from  Statistics  of  Cities,  Bulletin  No.  36  of  U.  S.  Department  of 
Labor,  September  1901,  p.  876-79. 

the  different  kinds  of  pavements  in  the  one  hundred  and 
thirty-five  cities  having  a  population  of  30,000  or  over  in  June, 
1901.  Notice  that  the  fourth  line  in  the  table  is  "granite  and 
Belgian  blocks,"  and  not  stone  blocks;  and  therefore  sandstone- 
and  limestonerblock  pavements  must  be  included  in  line  8,  which 
is  unfortunate  since  sandstone-block  pavements  have  substantially 
the  same  qualities  as  granite-block  pavements.  The  last  line  of 
the  table  under  the  head  of  "all  others, "  includes  sandstone  and 
limestone  block,  rubble,  shell,  tar  distillate,  granolithic,  slag  block, 
and  perhaps  telford — at  least  Boston,  Buffalo,  and  St.  Louis  usually 
separate  macadam  and  telford  pavements  in  their  official  reports. 
There  is  a  considerable  extent  of  sandstone-block  pavements, 
particularly  in  the  Lake  Cities.  In  1892,  Philadelphia  reported 
115  miles  of  rubble  pavement  (§  807),  which  was  14  per  cent  of  all 
the  pavements  in  that  city.  Some  of  the  Southern  cities  have 
rubble  pavements,  and  several  others  have  streets  paved  with  shells. 


AMOUNT   OF   DIFFERENT   KINDS    OF   PAVEMENTS. 


565 


874.  Of  the  2,061  miles  of  asphalt  pavements,  Philadelphia 
has  289  miles,  Greater  New  York  264,  Buffalo  224,  Washington 
125,  and  Chicago  103,  these  five  cities  having  practically  half  the 
asphalt  pavements  reported  in  Table  55.  Of  the  1,186  miles  of 
brick  pavements,  Philadelphia  has  128  miles,  more  than  twice  as 
much  as  any  other  city.  Of  the  1,034  miles  of  cobble  stone,  Balti- 
more has  321  miles  and  New  York  229  miles,  the  former  being 
90  per  cent  of  all  the  pavements  in  the  city  and  the  latter  13  per 
cent.  Of  the  2,020  granite-  and  Belgian-block  pavements  in  Table 
55,  New  York  has  459  miles  and  Philadelphia  358,  no  other  city 
having  more  than  88  miles.  The  milage  of  macadam  pavements 
in  the  five  largest  cities  is  as  follows :  New  York  766  miles,  Chicago 
387,  Boston  292,  St.  Louis  259,  and  Philadelphia  208.  Of  the 
1,313  miles  of  wood  pavement  in  Table  55,  Chicago  has  749  miles 
(58  per  cent  of  all  the  pavements  in  the  city),  and  Detroit  has  223 
(73  per  cent  of  all  the  pavements  in  the  city),  these  two  cities 
having  80  per  cent  of  all  the  wood  pavements  reported. 

875.  Table  56  gives  the  number  of  miles  and  relative  propor- 

TABLE  56. 
Number  of  Miles  and  Relative  Proportion  of  the  Different  Kinds 
of  Pavements  in  Two  Hundred  and  Sixty-two  American  Cities 
in  1890  * 


Ref. 

No. 

Kinds  of  Pavements. 

Miles. 

Per  Cent. 

1 

Asphalt — sheet  and  block 

394 

1*888 

1504 

3  858 

3  474 

969 

366 

3  2 

2 

Brick 

3 

Cobble  Stone 

15  1 

4 

Stone  Block 

12  1 

5 

Gravel 

31  0 

6 

Macadam. 

27  9 

7 

Wood 

7  8 

8 

All  others 

2  9 

Total 

12  453 

100  0 

*  Compiled  from  Social  Statistics  of  Cities,  Eleventh  U.  S.  Census,  1890,  p.  15-19. 

tions  of  the  different  kinds  of  pavements  in  two  hundred  and 
sixty-two  cities  having  a  population  in  1890  of  10,000  or  over. 
Table  56  is  given  in  the  same  form  as  Table  55  for  convenience  in 
making  comparisons.     Notice  that  no  brick  pavements  were  re- 


666  COMPARISONS   OF   PAVEMENTS.  [CHAP.  XVIII.. 

ported  separately  in  1890.  Notice  also  that  the  fourth  line  of 
Table  56  is  stone  block,  and  not  granite  and  Belgian  block  as  in 
the  corresponding  line  of  Table  55.  A  comparison  of  Tables  55 
and  56  shows  that  the  per  cent  of  asphalt  pavements  in  eleven 
years  increased  more  than  fourfold;  and  in  the  same  time  the  per 
cent  of  cobble-stone  and  of  gravel  pavements  decreased  more  than 
half,  while  that  of  macadam  and  of  wood  slightly  increased. 

876.  REQUIREMENTS  OF  AN  IDEAL  PAVEMENT.  The  perfect 
pavement  is  an  ideal  which  will  never  be  attained,  since  some  of 
the  qualities  required  in  a  perfect  pavement  are  antagonistic  to 
each  other.  For  instance,  perfect  durability  would  require  a 
pavement  without  friction,  for  friction  causes  wear  and  ultimately 
destruction  of  the  pavement;  but  without  friction  there  could  be 
no  adequate  foot  hold  for  horses  drawing  loads.  Again,  to  be  the 
least  injurious  to  horses,  n  pavement  should  be  soft  and  yielding; 
but  a  soft  and  yielding  pavement  is  opposed  to  ease  of  traction. 
The  conditions  to  be  fulfilled  by  the  ideal  pavement  will  first  be 
considered ;  and  subsequently  an  attempt  will  be  made  to  estimate 
the  degree  to  which  each  kind  of  pavement  approximates  the  per- 
fect ideal. 

A  perfect  pavement  should  satisfy  the  following  conditions : 

1.  It  should  be  low  in  first  cost. 

2.  It  should  be  durable,  i.  e.,  the  cost  of  perpetually  maintain- 
ing its  surface  in  good  condition  should  be  small. 

3.  It  should  have  a  smooth,  hard  surface,  so  as  to  have  a  low 
tractive  resistance. 

4.  It  should  afford  a  good  foot  hold  to  enable  horses  to  draw 
heavy  loads,  and  to  prevent  them  from  slipping  and  falling  and 
possibly  injuring  themselves  and  blocking  traffic. 

5.  It  should  be  smooth,  so  as  to  be  easily  cleaned. 

6.  It  should  be  comparatively  noiseless. 

7.  It  should  be  impervious,  so  as  to  keep  in  good  sanitary 
condition. 

8.  It  should  yield  neither  dust  nor  mud. 

9.  It  should  be  comfortable  to  those  who  ride  over  it. 

10.  It  should  not  absorb  heat  excessively. 

Each  of  the  ordinary  forms  of  pavements  will  be  considered 
under  each  of  the  above  requirements. 


KEQUIREMENTS   OF   AN   IDEAL   PAVEMENT.  567 

877.  Cost.  The  cost  of  construction  of  a  pavement  varies, with 
the  character  of  the  work  and  with  the  locality.  For  data  on  this 
subject,  see  the  several  kinds  of  pavements  in  the  preceding  chap- 
ters. 

878.  Durability.  The  durability  of  a  pavement  made  of  per- 
ishable material,  as  wood  and  to  some  extent  macadam,  gravel 
and  asphalt,  depends  upon  both  the  climate  and  the  traffic;  but 
in  general  the  durability  of  paving  materials  depends  chiefly  upon 
the  volume  of  the  traffic,  and  consequently  the  durability  of  differ- 
ent pavements  can  be  accurately  compared  only  when  the  nature 
and  the  amount  of  the  traffic  over  each  is  known.  Unfortunately 
there  are  very  little  definite  data  as  to  the  amount  of  traffic  upon 
American  pavements.  Not  infrequently  the  traffic  on  a  particular 
pavement  is  referred  to  as  being  "heavy"  or  " light,"  but  such 
general  terms  are  practically  worthless  in  comparing  the  durability 
of  different  kinds  of  pavements.  Only  a  few  detailed  observa- 
tions have  been  made  concerning  the  traffic  upon  American  pave- 
ments, and  they  are  somewhat  antiquated. 

879.  Travel  Census.  The  first  and  the  most  elaborate  census 
of  street  travel  taken  in  this  country  was  made  in  1885  under  the 
direction  of  Capt.  F.  V.  Greene.  Table  57,  page  568,  gives  a  sum- 
mary of  the  results,  and  the  following  extracts  from  Captain 
Greene's  article  *  explain  the  details  of  the  method  of  making 
the  observations. 

"The  observations  were  made  during  the  months  of  October 
and  November,  1885,  by  the  employees  of  the  Barber  Asphalt 
Paving  Company,  which  has  an  office  and  works  in  the  ten  large 
cities.  In  the  arrangements  for  taking  the  observations  two 
objects  were  kept  in  view:  first,  to  leave  as  little  as  possible  to 
the  judgment  of  the  observer;  and  second,  to  make  the  record 
permanent,  so  that  it  could  be  preserved  for  examination  in  all  its 
details  at  any  time. 

"The  agent  in  each  city  was  instructed  to  select  the  three 
streets  in  that  city  paved  with  stone,  asphalt,  and  wood  (if  any 
existed)  which,  by  common  report,  had  the  heaviest  traffic  on 
the  class  of  pavement  used  on  that  street.     The  record  was  in 


*  Trans.  Amer.  Soc.  Civil  Eng'rs,  Vol.  15,  p.  123-38. 


568 


COMPARISONS    OF    PAVEMENTS.  [CHAP.    XVIII. 


TABLE  57. 
Travel  on  Certain  Streets  in  Various  American  Cities  in  1885. 


Locality. 


City. 


New  York. . 


4  Philadelphia 

5 

6 


Chicago 


Boston 


St.  Louis 


New  Orleans 


Washington 


Buffalo. 


Louisville , 


Omaha 


Street. 


Broadway,  near  Pine 

Fifth  Ave.,  opp  Worth  Monum't 
Wall,  corner  of  Broad 

Broad,  in  front  of  P.R.R.  Depot 
Filbert,  in  front  of  City  Hall  . . . 
Chestnut,  corner  of  Fourth 

Wabash,  near  Lake 

Clark,  near  Madison 

La  Salle,  near  Locust 

Dearborn,  opp.  Washington  P'k 

Devonshire,  opp.  Post  Office 

Devonshire,  near  Milk 

Kilby,  near  State 

Washington 

Arch,  near  Summer 

Court  Square 

Locust,  near  Beaumont 

Broadway,  near  Olive 

Pine,  near  Garrison 

Chestnut,  near  Beaumont 

Olive,  near  Beaumont 

Tchoupitoulas,  near  Poydras. . . . 
St.  Charles,  near  Washington. . . 


15th,  opposite  Treasury 

9th,  between  D  and  E 

7th,  between  D  and  E 

6th,  between  Pa.  Ave.  and  B. .  . 


Main,  near  Swan 

Main,  near  Bouck  Ave. 
Linwood,  near  Ferry. . 
Main,  near  Glenwood . , 


Main,  near  3d 

8th,  near  Walnut. . 
7th,  near  Jefferson. 


Douglass,  near  15th. 
Farnham,  near  14th, 


o  — 

Number  of  Tons. 

1 

$*i 

Total 

Per 

T3  o> 

40 

per  Day. 

Vehicle. 

P^OQ 

10  905 

1.39 

273 

40 

3  744 

.68 

94 

27 

2  357 

1.00 

87 

65 

9  237 

1.52 

142 

65 

6  302 

1.24 

97 

26 

1928 

1.06 

74 

50 

7  561 

2.08 

151 

45 

6  398 

1.46 

142 

36 

2  756 

.90 

77 

38 

2  604 

1.11 

69 

27 

5  301 

.99 

196 

32 

5  028 

1.02 

157 

26 

3  265 

.93 

126 

39 

2  938 

.80 

75 

26 

1  130 

.79 

43 

24 

744 

.67 

32 

36 

3  691 

1.13 

103 

50 

3  618 

1.23 

72 

36 

2  554 

1.16 

7C 

36 

942 

.90 

27 

36 

259 

.84 

7 

40 

6  204 

1.81 

155 

30 

1065 

.94 

35 

70 

4  622 

1.02 

66 

50 

1688 

.87 

34 

50 

1445 

.88 

29 

60 

1289 

1.01 

21 

56 

2  613 

.83 

47 

42 

1505 

1.88 

36 

38 

825 

1.47 

22 

50 

714 

1.24 

14 

61 

4  176 

1.25 

69 

36 

2  402 

1.05 

67 

35 

977 

1.05 

28 

63 

2  967 

.62 

47 

60 

1449 

.59 

24 

REQUIREMENTS   OF   AN   IDEAL   PAVEMENT.  569 

every  case  made  on  six  consecutive  days  (Sunday  excepted)  at 
the  same  place,  and  it  was  continuous  from  7  a.  m.  to  7  p.  m.,  except 
when  darkness  prevented.  No  addition  was  made  for  this  omission, 
no  record  was  kept  during  the  night,  and  no  addition  was  made 
as  an  estimate  of  night  traffic. 

"The  printed  instructions  issued  to  each  observer  contained 
the  following  rules  as  a  guide  in  estimating  the  weights  of  vehicles: 

"  '  1-horse  carriages,  empty  or  loaded,  } 

1-horse  wagons,  empty  or  light-loaded,  r  Less  than  1  ton. 

1-horse  carts,  empty,  ) 

1-horse  wagons,  heavy-loaded,  } 

1-horse  carts,  loaded,  r  Between  1  and  3  tons. 

2-horse  wagons,  empty  cr  light-loaded,  J 

Wagons  and  trucks  drawn  by  two   or 


more  horses,  heavy-loaded,  f  0ver  three  tons« 

Special  note  will  be  made,  in  the  column  of  remarks,  of  any  unusu- 
ally heavy  loads,  such  as  6-horse  trucks  loaded  with  stone  or  iron, 
and  an  estimate  be  given  of  their  weight.' 

"The  traffic  is  divided  into  three  classes,  light  weight  (less 
than  one  ton),  medium  weight  (between  one  and  three  tons),  and 
heavy  weight  (more  than  three  tons);  and  in  order  to  reduce  the 
personal  equation  of  the  different  observers  to  a  minimum,  the 
directions  specify  what  classes  of  vehicles  are  to  be  counted  in  each 
class  of  weight.  Nothing  is  then  left  to  the  observer's  judgment 
and  estimation  except  the  question  of  '  heavy '  and  '  light '  loads  in 
one-horse  and  two-horse  wagons.  The  result  of  different  estima- 
tion in  this  respect  between  two  observers  would  simply  change  a 
portion  of  the  vehicles  from  one  class  to  another,  and  the  error  in 
the  final  result  could  hardly  exceed  5  per  cent. 

"The  weight  of  the  horses  is  discarded  altogether,  not  because 
they  do  not  constitute  a  factor  in  the  wear  of  the  pavement,  but 
because  they  were  discarded  in  the  English  reports,  and  it  was 
desired  as  far  is  possible  to  make  comparisons  with  them.  The 
addition  that  would  have  to  be  made  if  the  horses  were  included 
would  vary  with  the  traffic.  On  streets  where  light  vehicles  pre- 
dominate (as  on  Fifth  Avenue,  New  York),  the  addition  to  the  ton- 
nage by  including  the  weight  of  the  horses  would  be  about  85  per 
cent;  on  streets  with  heavy  vehicles  (such  as  Wabash  Avenue, 


570  COMPARISONS    OF    PAVEMENTS.  [CHAP.   XVIII. 

Chicago),  it  would  be  only  about  40  per  cent;  and  for  other  streets 
it  would  be  between  these  two  limits. 

"  The  average  daily  traffic  was  obtained  by  dividing  the  total 
record  for  six  days  by  six.  To  obtain  the  tonnage,  the  light- 
weight vehicles  were  estimated  to  average  one  half  ton  each  (in- 
cluding their  loads),  the  medium -weight  two  tons,  and  the  heavy- 
weight four  tons.  Multiplying  the  daily  average  of  vehicles  in 
each  class  by  these  figures  and  adding  together  the  products,  the 
total  tonnage  was  obtained ;  and  dividing  this  by  the  width  be- 
tween curbs,  we  get  the  daily  average  tonnage  per  foot  of  width. 

"  The  average  tonnage  per  vehicle  is  an  almost  infallible  indicator 
of  the  character  of  the  street,  i.  e.,  whether  devoted  to  residential 
or  business  purposes.  It  ranges  from  0.68  tons  on  Fifth  Avenue 
in  New  York  to  2.08  on  a  portion  of  Wabash  Avenue  in  Chicago. 
The  same  character  is  indicated  by  the  proportions  of  light  and 
heavy  vehicles  on  the  street.  On  Fifth  Avenue,  for  instance,  91 
per  cent  of  all  the  vehicles  weigh  less  than  one  ton,  while  on  Wabash 
Avenue  only  25  per  cent  of  them  have  so  little  weight.  The  general 
average  for  all  the  cities  is  as  follows:  less  than  one  ton,  67  per 
cent,  between  one  and  three  tons,  26  per  cent;  more  than  tnree 
tons,  7  per  cent." 

880  During  the  years  1888  and  1889  the  Warren-Scharf  As- 
phalt Paving  Co.*  made  observations  on  twenty-five  streets  in 
ten  cities  on  seven  kinds  of  pavements,  the  length  of  the  observa- 
tions for  a  particular  street  varying  from  one  to  seven  days.  In 
these  observations  the  tonnage  including  both  horses  and  vehicles, 
varied  from  6  to  138  tons  per  day  per  foot  of  width  of  pavement. 

In  1892  the  Board  of  Public  Works  of  Indianapolis,  Ind.,  took 
a  travel  census  of  thirteen  of  the  principal  streets  of  that  city,  the 
observations  being  made  according  to  the  system  employed  by 
Captain  Greene  (§  879). f  The  travel  varied  from  16  to  110  tons 
per  day  per  foot  of  width  of  pavement. 

In  1892  a  census  of  travel  was  taken  on  twenty-five  streets 
of  Montreal,  Canada. J     The  method  was  the  same  as  that  em- 

*  Advertising  pamphlet  published  by  the  company. 

f  Paving  and  Municipal  Engineering  (now  Municipal  Engineering),  Vol.  3.  p/ 
68-69. 

J  Annual  Report  of  City  Engineer  for  1893,  p.  295-319. 


REQUIREMENTS    OF    AN    IDEAL    PAVEMENT. 


57. 


ployed  by  Captain  Greene  (§  879)  except  that  the  observations 
were  made  from  7  a.m.  to  6  p.m.,  and  except  further  that  the 
weight  of  the  horses  was  included,  the  weight  of  each  being  esti- 
mated at  half  a  ton.  The  tonnage  varied  from  17  to  146  tons  per 
day  per  foot  of  width. 

The  City  Engineer's  Report  of  Toronto,  Canada,  for  1894  con- 
tains the  details  of  a  travel  census  upon  three  streets  in  that  city 
made  according  to  Greene's  method,  except  that  the  weight  of  the 
horses  was  estimated  at  half  a  ton  each  and  was  included.  The 
tonnage  varied  from  32  to  79  tons  per  day  per  foot  of  width. 

881.  Table  58  gives  the  travel  record  of  certain  streets  in 
London  and  Liverpool.*      The  observations  were  not  all  made 

TABLE  58. 
Travel  on  Certain  Streets  in  London  and  Liverpool 


City. 


1 

London 

2 

a 

3 

u 

4 

si 

5 

a 

6 

7 

it 

8 

9 

U 

10 

it 

11 

tt 

12 

a 

13 

K 

14 

c 

15 

it 

16 

M 

17 

t< 

18 

Liverpool . . 

19 

20 

21 

$* 

Locality. 


Street. 


Gracechurch 
King  William.. .  . 

Poultry 

Strand  and  Fleet. 

Parliament 

Oxford 

Cheapside 

Leadenhall 

Piccadilly 

Euston 

Brompton 

King  William  . .  . 

Edgeware 

Regent 

King's 

Victoria 

Sloane 


(Not  named) 


Great  Howard 
Bold 


Pavement. 


Kind. 


Asphalt 
Wood 

Asphalt 

Wood 

Macadam 

W^ood 

Asphalt 

Macadam 
Granite 
Wrood 
Granite 

(4 

Macadam 
Wood 

Macadam 
Wood 

Granite 

Wood 


32 
40 
22 
37 
45 
57 
32 
30 
37 
44 


32 
43 
52 


40 


Number  of  Tons 


Per  Day. 


13  507 

16  484 

8  330 

13  596 

14  380 

17  076 

9  260 
7  588 
9  358 

10  658 


6  506 

8  376 

9  668 


5  780 


Per 

Vehicle, 


1.11 

1.06 

1.02 

.84 

1.01 


01 

98 

08 

87 
88 


1.02 

1.02 

.90 


.96 


5* 

O  l< 

o  <u 

£3 


422 
412 
378 
367 
322 
300 
290 
253 
253 
242 
216 
203 
195 
186 
156 
145 
93 

382 
232 
231 
100 


*  Trans.  Amer.  Soc.  of  Civil  Eng'rs.  Vol.  15,  p.  131. 


572  COMPARISONS   OF   PAVEMENTS.  [CHAP.   XVIII, 

under  the  same  direction,  but  not  much  is  known  concerning  the 
methods  employed.  Some  of  the  observations  were  made  from 
8  a.  m.  to  8  p.  m.,  and  some  from  7  a.  m.  to  11  p.  m. 

In  Paris  it  is  customary  to  state  the  travel  in  number  of  *  col- 
lars "  per  unit  of  width,  no  tonnage  being  given. 

882.  It  is  desirable  that  engineers  in  charge  of  streets  and 
roads  should  ascertain  by  direct  observation  the  amount  of  ton- 
nage passing  over  each  particular  pavement,  in  order  that  the 
service  per  unit  of  cost  of  different  pavements  may  be  accurately 
compared.  The  only  measure  of  the  durability  of  a  pavement 
is  the  amount  of  travel  tonnage  it  will  bear  before  it  becomes  so 
worn  that  the  cost  of  replacing  it  is  less  than  the  expense  incurred 
by  its  use. 

Notice  that  some  of  the  above  results  include  only  vehicular 
travel  and  others  include  both  vehicles  and  horses.  No  systematic 
observations  have  ever  been  made  to  determine  the  relative  destruc- 
tiveness  of  horses  and  vehicles;  but  apparently,  compared  ton 
for  ton,  horses  are  more  destructive  than  vehicles.  The  sharp 
blows  of  horses'  shoes,  particularly  if  they  have  heel  and  toe-  calks, 
are  very  destructive  to  stone-block  and  brick  pavements,  as  they 
spall  off  the  edges  of  the  blocks. 

883.  Modifying  Elements.  Although  the  effect  of  travel  is 
dependent  chiefly  upon  the  number  of  tons  per  foot  of  width,  its 
influence  is  modified  somewhat  by  (1)  the  character  of  the  pave- 
ment, (2)  the  state  of  repairs,  (3)  the  degree  of  cleanliness,  (4)  the 
presence  or  absence  of  car  tracks,  (5)  the  width  of  pavement,  (6) 
the  character  of  the  traffic,  and  (7)  the  climate. 

1.  The  durability  of  a  particular  kind  of  pavement  will  vary 
with  the  details  of  the  method  of  construction.  The  foundation 
may  be  more  •  or  less  rigid,  the  materials  may  differ  greatly  in 
durability,  with  any  form  of  block  pavement  the  joints  may  be 
more  or  less  open,  and  the  surface  may  also  vary  more  or  less  in 
roughness. 

2.  The  durability  will  depend  upon  the  care  employed  in  re- 
pairing the  pavement.  If  holes,  depressions,  or  ruts  are  allowed 
to  remain  for  any  length  of  time,  whatever  the  material  the  pave- 
ment will  wear  abnormally  fast. 

3.  The  degree  of  cleanness  will  materially  modify  the  durability 


REQUIREMENTS   OF   AN   IDEAL   PAVEMENT.  573 

of  a  pavement.  An  imperishable  material  is  benefited  by  a  cov- 
ering of  detritus,  since  it  serves  as  a  carpet  to  protect  the  pave- 
ment ;  and  if  the  covering  is  heavy  enough  the  pavement  virtually 
becomes  a  foundation  and  is  entirely  protected  from  wear.  On 
the  other  hand,  the  decay  of  a  perishable  material,  as  wood  and 
asphalt,  is  hastened .  by  a  covering  of  street  dirt  which  collects: 
moisture  and  hastens  the  decay  and  disintegration  of  the  pavement. 

4.  The  presence  of  a  street-car  track  on  a  street  concentrates 
traffic  at  the  two  sides,  thus  virtually  narrowing  the  street,  and  also 
causes  the  travel  to  go  substantially  in  one  track,  a  result  which 
is  particularly  destructive  of  gravel  and  macadam  roads. 

5.  The  wider  a  pavement  the  more  evenly  will  it  wear,  and 
consequently  the  longer  it  will  last.  If  several  irregular  lines  of 
travel  can  be  maintained,  the  wear  will  be  much  more  even  and 
the  durability  greater  than  if  the  vehicles  are  restricted  to  prac- 
tically a  single  line. 

6.  The  durability  of  the  pavement  will  vary  with  the  weight 
per  unit  width  of  tire,  the  method  of  shoeing  the  horses,  and  the 
rapidity  of  the  travel.  In  Europe,  the  weight  per  unit  of  width 
of  tire  is  generally  regulated  by  law,  and  calks  on  the  horses'  shoes 
are  prohibited;  but  in  America  there  are  no  such  restrictions. 
Rapid  travel  is  more  destructive  to  a  block  pavement  than  slow 
travel. 

7.  The  climate  affects  the  durability  of  several  kinds  of  pave- 
ment. The  durability  of  a  wood  pavement  is  affected  by  the  heat 
and  the  moisture  conditions,  that  of  macadam  and  gravel  by 
moisture  and  winds,  and  that  of  asphalt  by  moisture,  particularly 
by  street  sprinkling.  Sprinkling  materially  affects  the  durability 
of  wood  pavement,  as  is  shown  where  a  strip  is  ordinarily  left  un- 
sprinkled  for  a  foot-way. 

884.  Comparative  Durability.  Until  more  complete  data  con- 
cerning the  volume  of  travel  on  pavements  and  the  amount  oi 
wear  are  obtained,  it  will  be  impossible  to  make  any  reliable  esti- 
mates as  to  the  durability  of  different  paving  materials. 

It  is  generally  conceded  that  granite  block  is  the  most  dur- 
able paving  material,  especially  under  very  heavy  loads. 

Asphalt  and  brick  rank  next  to  granite,  and  when  well  con- 
structed give   excellent   service   except   perhaps  under  the   very 


574  COMPARISONS   OF   PAVEMENTS.  [CHAP.  XVIII. 

heaviest  traffic ;  although  it  should  be  noted  that  as  the  method  of 
preparing  and  laying  these  materials  becomes  better  understood, 
they  are  being  laid  under  heavier  and  heavier  traffic.  For  example, 
within  the  last  year  or  two  artificial  sheet  asphalt  has  replaced 
granite  block  on  Broadway  in  the  most  congested  district  of  New 
York  city — a  street  probably  having  the  most  travel  of  any  in  this 
country  (see  Table  57,  page  568).  Again,  only  a  few  years  ago  it 
was  considered  that  bricks  were  suitable  only  for  small  cities; 
but  now  Philadelphia,  the  third  largest  city  on  this  continent,  has 
128  miles  of  brick  pavements.  The  production  of  granite  paving 
blocks  has  decreased  one  half  in  the  past  ten  years,  apparently 
because  of  the  introduction  of  asphalt  and  brick  pavements.  The 
relative  durability  of  brick  and  asphalt  is  a  matter  of  doubt,  both 
materials  showing  varying  results  due  to  differences  in  the  quality 
of  the  material  and  to  the  method  of  construction.  The  following 
examples  show  the  possible  durability  of  these  two  materials.  A 
brick  pavement  on  concrete  with  cement-filled  joints  laid  on  one 
of  the  principal  business  streets  in  Terre  Haute,  Ind.,  after  eleven 
years'  service  without  repairs,  showed  a  maximum  general  wear 
of  only  ?V  to  ^V  °f  an  mcn  with  a  few  holes  showing  a  wear  of  |*  of 
an  inch,  the  population  of  the  city  increasing  in  the  meantime  from 
30,000  to  36,600  and  there  being  a  double  track  car-line  on  the 
street.  An  asphaltic  limestone  pavement  on  Cheapside,  London, 
which  has  a  daily  travel  of  290  tons  per  foot  of  width  (see  Table 
58,  page  571),  wore  down  about  1  inch  in  seventeen  years.  It  is 
said  that  the  average  life  of  asphaltic  limestone  pavements  in 
London  and  Paris  is  about  seventeen  years.  An  artificial  sheet 
asphalt  pavement  on  Pennsylvania  Avenue,  Washington,  D.  C, 
was  re-laid  after  thirteen  years'  use.  The  method  of  repairing 
asphalt  pavements,  both  artificial  and  natural  rock,  may,  however, 
make  such  examples  as  the  last  two  misleading.  For  data  on  cost 
of  maintenance  of  asphalt  pavements,  see  §  670-74. 

Round-block  coft-wood  pavements  are  lacking  in  durability, 
but  rectangular  blocks  of  both  soft  and  hard  wood  have  given 
satisfactory  service  under  heavy  traffic  in  London  and  Paris.  For 
example,  at  the  end  of  Westminster  Bridge,  where  the  traffic  from 
6  a.  m.  to  6  p.  m.  is  334  tons  per  foot  of  width,  of  which  15  per  cent 
is  heavy  omnibuses^  the  mean  of  six  years'  wear  of  jarrah  rectangu* 


REQUIREMENTS   OF   AN"   IDEAL   PAVEMENT.  575 

lar  blocks  was  0.16  inch  per  year.*  On  Euston  Road,  London, 
where  the  travel  not  including  horses  was  529  tons  per  24  hours 
per  foot  of  width,  of  which  7.7  per  cent  was  heavy  omnibuses, 
the  maximum  wear  of  the  jarrah  and  karri  rectangular  blocks  was 
0.08  of  an  inch  per  annum  and  yellow  deal  0.46  of  an  inch.f  At 
another  place  on  Euston  Road,  where  the  travel,  not  including 
horses,  was  381  tons  per  24  hours  per  foot  of  width,  the  maximum 
wear  of  jarrah  blocks  was  T%  of  an  inch,  the  minimum  being  T\  of 
an  inch,  and  the  average  J  inch.]; 

Broken  stone  and  gravel  wear  rapidly  under  moderately  heavy 
travel,  and  are  suitable  only  for  residence  and  suburban  streets, 
and  for  park  roads  and  pleasure  drives. 

885.  In  trying  to  determine  the  probable  life  of  a  pavement, 
two  facts  should  not  be  overlooked,  viz.,  (1)  The  average  wear 
does  not  determine  the  life  of  a  pavement,  since  even  the  most  care- 
fully constructed  pavements  wear  so  unevenly  as  to  require  re-lay- 
ing before  the  wearing  coat  is  entirely  worn  out.  This  is  true  of 
macadam  and  sheet  asphalt  which  have  a  comparatively  thin 
wearing  coat,  and  is  particularly  true  of  pavements  made  of  blocks, 
as  wood,  brick,  and  stone,  since  the  edges  of  the  blocks  wear  off 
and  leave  the  top  face  rounded,  and  when  the  pavement  reaches 
this  stage  the  wear  is  much  more  rapid  than  previously.  (2)  In  a 
block  pavement  the  blocks  must  have  a  certain  depth  to  enable 
them  to  keep  their  place,  and  consequently  bricks  and  shallow 
wood  blocks  can  not  be  worn  more  than  about  half-way  through. 
If  the  blocks  are  made  deeper,  the  durability  of  the  pavement  is 
not  increased  much,  if  any,  since  owing  to  unequal  wear  the  pave- 
ment must  be  re-laid  before  any  considerable  depth  is  worn  off. 

Asphalt  and  trap-top  macadam  have  some  decided  economic 
advantages  over  other  forms  of  pavements,  since  the  wearing  sur- 
face consists  of  a  comparatively  thin  wearing  coat  that  can  be  re- 
placed when  it  is  worn  out  or  wears  rough,  without  proportionally 
as  much  loss  as  when  a  block  pavement  is  re-surfaced.      A  further 

*  J.  F.  Norrington,  Surveyor  of  Lambeth,  Proc.  Assoc.  Municipal  and  County 
Engineers,  Vol.  22,  p.  93. 

f  W  N.  Blair,  Assoc.  M.  Inst.  C.  E.,  Engineer  St.  Pancras  Vestry,  Proc.  Assoc. 
Municipal  and  County  Engineers,  Vol.  22,  p.  86-87. 

X  Ibid.,  p.  89. 


576  COMPARISONS   OF    PAVEMENTS.  [CHAP.   XVIII. 

economic  advantage  of  these  pavements  is  that  when  holes  begin 
to  form  a  patch  can  be  applied  and  thus  the  uniformity  of  the 
surface  may  be  preserved  and  the  life  of  the  pavement  be  extended. 
Trap-topped  macadam  has  an  economic  advantage  over  asphalt, 
in  that  when  it  is  re-surfaced  the  old  material  is  not  thrown  away 
but  is  simply  picked  loose  and  mixed  with  the  new  stone. 

886.  Tractive  Resistance.  Table  9,  page  31,  gives  the  tractive 
resistance  of  different  pavements,  from  which  it  is  seen  that  the 
rank  of  the  various  pavements  according  to  tractive  resistance,  in 
order  beginning  with  the  one  offering  the  least  resistance,  is  about 
as  follows:  Asphalt  during  cold  weather,  brick,  best  macadam, 
asphalt  during  warm  weather,  rectangular  wood  block,  good 
gravel,  new  cylindrical  wood  block,  carefully  dressed  stone  block, 
ordinary  macadam,  ordinary  gravel,  ordinary  stone  block,  old 
cylindrical  wood  block,  cobble  stone.  The  tractive  resistance 
will  vary  greatly  with  the  state  of  repair  of  the  surface. 

Many  attempts  have  been  made  to  compute  the  financial  advan- 
tage of  a  decreased  tractive  resistance,  but  it  is  impossible  to  deter- 
mine its  value  with  any  degree  of  accuracy,  although  it  is  certain 
that  the  tractive  resistance  of  the  pavements  of  a  city  are  impor- 
tant factors  in  determining  the  cost  of  conducting  transporta- 
tion. Ease  of  traction  is,  however,  not  relatively  as  important 
for  city  pavements  as  for  country  roads,  since  in  the  latter  ease 
of  traction  is  a  matter  of  first  importance  (see  §  4-9),  while  in  the 
former  it  is  comparatively  unimportant  (see  §  442).  On  the  other 
hand,  the  cost  of  transportation  per  ton-mile  is  considerably  more 
in  the  cities  than  in  the  country. 

887.  Slipperiness.  The  method  of  comparing  pavements  in 
this  respect  is  to  determine  the  distance  a  horse  travels  on  the 
different  pavements  before  he  falls.  The  most  complete  observa- 
tions made  in  the  United  States  to  ascertain  the  prevalence  of 
accidents  on  the  different  pavements  were  made  under  the  direc- 
tion of  Capt.  F.  V.  Greene.*  The  observations  were  made  from 
7  a.m.  to  7  p.m.  on  six  consecutive  days  in  October  and  Novem- 
ber, 1885,  in  ten  of  the  leading.  American  cities  on  thirty-three 
streets  having  the  heaviest  traffic  for  each  kind  of  pavement  in 


*  Trans.  Amer.  Soc.  of  Civil  Engineers,  Vol.  15,  p.  123-28. 


REQUIREMENTS    OF   AN    IDEAL    PAVEMENT. 


57? 


the  particular  city.  The  number  of  horses  observed  on  asphalt 
pavements  were  360,254,  on  granite  376,384,  and  on  wood 
70,914;  and  the  number  of  miles  traveled  by  the  horses  while 
under  observation  was  41,427  on  the  asphalt  pavements,  34,723 
on  the  granite,  and  4,901  on  the  wood.  A  summary  of  the  results 
is  shown  in  Table  59. 


TABLE  59. 

Miles  Traveled  by  a  Horse  on  American  Pavements  Before  an  Acci- 
dent Occurs. 


Ref. 
No. 

9              Kind  of  Pavement. 

Fall  on     |    Fall  on 
Knees.      Haunches. 

Complete 
Fall. 

Accident 
of  Any- 
Kind 

1 
2 

Asphalt,  artificial  sheet. 

Granite  Block 

1534 
510 
408 

2  180 

5  954 

983 

164V 

3  472 

4  901 

583 
413 

3 

Wood  * 

272 

888.  An  elaborate  series  of  observations  was  made  in  Lon- 
don in  1873  by  Col.  William  Haywood.f  The  three  classes  of 
pavements,  asphalt,  granite,  and  wood,  were  observed  as  nearly 
as  possible  under  the  same  conditions  of  space,  weather,  gradi- 
ents, etc.,  on  fifty  different  days.  The  results  are  shown  in 
Table  60. 


TABLE  60. 
Miles  Traveled  by  a  Horse  on  London  Pavements  Before  an  Acci- 
•    dent  Occurs. 


Ref. 
No. 

Kind  of  Pavement. 

Dry 
Weather. 

Damp 
Weather. 

Wet 
Weather. 

1 

2 

Asphaltic  Limestone 

Granite  Block 

223 

78 
646 

125 

168 
193 

192 
537 

3 

Rectangular  Wood  Block. . . . 

432 

*  The  kind  of  wood  block  is  not  stated,  and  apparently  it  can  not  now  be  deter- 
mined. 

f  Report  to  the  Honorable  the  Commissioners  of  Sewers  of  the  City  of  London 
on  the  Accidents  to  Horses  on  Carriageway  Pavements.  By  William  Haywood, 
Engineer  and  Surveyor  to  the  Commission.  London,  1873.  Published  also  on 
pages  297-317  of  Streets  and  Highways  in  Foreign  Cities,  Vol.  Ill  of  Special  Con- 
sular Reports,  Washington,  1891. 


578  COMPARISONS   OF    PAVEMENTS.  [CHAP.    XVIII. 

The  average  distance  traveled  by  a  horse  before  an  accident 
occurred  was  as  follows: 

On  Asphaltic  Limestone 191  miles 

On  Granite  Block 132     " 

On  Rectangular  Wood  Block 330     " 

As  a  result  of  the  above  observations,  the  following  conclu- 
sions were  drawn.  "  Slight  rain  makes  asphalt  and  wood  more 
slippery  than  they  are  at  other  times.  On  asphalt  :he  slipperi- 
ness  begins  almost  immediately  after  the  rain  commences, 
while  wood  requires  more  rain  before  its  worst  condition  ensues. 
The  slipperiness  lasts  longer  upon  wood,  on  account  of  its  absorb- 
ent nature,  than  it  does  upon  the  asphalt.  When  dry  weather 
comes  after  the  rain,  asphalt  is  in  its  most  slippery  condition 
and  horses  fall  upon  it  very  suddenly.  Wood  is  frequently 
in  that  peculiar  condition  of  surface  in  which  horses  slip  or 
slide  along  without  falling.  A  small  quantity  of  dirt  on  asphalt 
makes  it  very  slippery.  In  damp  weather  granite  blocks  be- 
come very  greasy  and  slippery;  in  dry  weather,  if  they  are  of  a 
hard  variety,  the  surface  polishes  and  becomes  rounded  and  the 
only  foot  hold  is  by  the  joints  between  the  blocks." 

889.  The  difference  in  the  results  for  slipperiness  of  pave- 
ments in  London  and  in  American  cities  may  be  due  in  the 
case  of  the  wood  and  the  stone  pavements  to  climatic  causes. 
London  is  more  damp  and  foggy  than  any  one  of  the  American 
cities  in  which  the  traffic  was  observed,  and  therefore  its  pave- 
ments would  be  more  slippery.  The  difference  in  the  case  of 
asphalt  may  be  accounted  for  by  the  difference  in  the  character 
of  the  material.  The  asphalt  pavements  in  London  are  made 
from  asphaltic  limestone,  which  makes  a  very  smooth,  hard 
surface;  while  the  American  pavements  are  made  from  natural 
bitumen  mixed  with  sand,  which  forms  a  rough,  granular  sur- 
face. Further,  in  London,  and  generally  in  Europe,  the  horses' 
shoes  have  no  calks,  and  therefore  they  will  slip  more  than  in 
America  where  shoes  with  calks  are  the  rule. 

The  slipperiness  of  a  pavement  varies  greatly  with  the  de- 
gree of  its  cleanliness.  The  slipperiness  of  an  asphalt  pavement 
can  be  decreased  by  sprinkling  coarse  sand  over  the  surface, 
and  the  slipperiness  of  wood  can  be  greatly  decreased  by  strew- 


REQUIREMENTS    OF    AX    IDEAL   PAVEMENT.  579 

Ing  small  pebbles  over  it,  both  of  which  remedies  are  frequently 
used  in  London  and  Paris. 

890.  No  observations  similar  to  the  preceding  have  been  made 
for  brick  pavements,  but  it  is  probable  that  they  are  less  slippery 
than  asphalt,  wood,  or  stone  block.  Macadam  and  gravel  are 
the  least  slippery  of  any  of  the  pavements  under  consideration. 

891.  Ease  of  Cleaning.  The  facility  with  which  a  pavement 
may  be  cleaned  is  an  important  matter  both  economically  and 
esthetically.  Col.  Geo.  E.  Waring,  noted  for  his  service  as  Street 
Cleaning  Commissioner  of  New  York  city,  in  1896  estimated 
that  if  all  the  streets  of  New  York  city  were  paved  with  asphalt 
where  the  grades  would  permit,  the  cost  of  street  cleaning  would 
be  reduced  from  $1,200,000  to  $700,000  per  year.  At  that 
time  New  York  had  431  miles  of  pavement  of  which  94  were 
asphalt,  and  the  above  annual  saving  is  equal  to  3  per  cent  of 
the  cost  of  laying  asphalt  pavements  upon  all  of  the  streets  not 
already  asphalted. 

Sheet  asphalt  pavements  are  most  easily  cleaned,  and  next 
in  order  are:  asphalt  blocks,  wood  blocks  with  close  joints, 
brick  with  joints  filled  with  tar  or  hydraulic  cement,  stone 
block  with  tar  or  cement  joints,  ordinary  stone  block,  round 
wood  block,  cobble  stone. 

Macadam  and  gravel  are  smooth  and  for  this  reason  are 
easily  cleaned;  but  their  surfaces  grind  up  into  powder,  particu- 
larly under  dense  or  heavy  travel,  and  for  this  reason  there  is 
considerable  detritus  to  be  removed,  a  fact  which  adds  to  the 
expense  of  cleaning. 

892.  Noiselessness.  The  noise  made  by  travel  upon  a  pave- 
ment has  an  important  effect  upon  the  comfort  and  health  of  the 
people  using  the  pavement  or  living  adjacent  to  it.  A  quiet  pave- 
ment is  particularly  desirable  adjacent  to  office  buildings,  schools, 
churches,  hospitals,  etc.;  and  the  noise  of  travel  upon  a  rough 
pavement  aggravates,  if  it  does  not  cause,  nervous  disorders. 

On  sheet  asphalt  the  only  noise  is  the  sharp  click  of  the 
horses'  shoes;  and  on  asphalt  block  there  is  the  click  of  the  feet 
and  a  slight  rumbling  of  the  wheels  over  the  joints,  particularly 
if  the  blocks  were  not  laid  very  close  together.  Horses'  feet 
make  considerable  noise  on  all  brick  pavements,  and  wheels 


580  COMPARISONS   OF   PAVEMENTS.  [CHAP.   XVIII. 

produce  a  decided  roar  on  pavements  made  of  bricks  or  blocks 
having  rounded  corners,  at  least  while  the  pavements  are  com- 
paratively new;  but  if  the  bricks  have  square  edges  and  the 
joints  are  filled  with  tar  or  hydraulic  cement,  there  is  only  a  little 
rumbling.  Stone-block  pavements  are  the  most  objectionable 
in  this  respect,  producing  a  continual  roar  due  both  to  the 
rumbling  of  the  wheels  and  to  the  blows  of  the  horses'  shoes. 
Upon  wood  pavements  the  horses'  feet  produce  no  noticeable 
noise;  while  the  wheels  make  a  dull  rumbling  noise,  but  not 
loud  enough  to  be  seriously  objectionable.  Macadam  and  gravel 
are  more  quiet  than  wood. 

In  order  of  their  noise,  pavements  rank  about  as  follows: 
stone  block,  brick,  asphalt,  wood,  gravel,  macadam. 

893.  Healthfulness.  The  effect  of  a  pavement  upon  the 
health  of  the  residents  in  its  locality  will  depend  upon  the  ten- 
dency of  the  materials  composing  it  to  decay  and  also  upon  its 
permeability.  Wood  is  the  only  paving  material  that  is  subject 
to  decay,  and  is  also  the  only  material  that  is  in  itself  permeable. 
The  gradual  decay  of  the  wood  is  not  in  itself  a  serious  menace 
to  health;  but  the  decaying  wood  makes  a  lodging  place  for 
filth  and  disease  germs.  The  permeability  of  any  wood  block 
is  small  as  compared  with  that  of  the  wide  joints  of  round  wood- 
blocks and  of  ordinary  stone  blocks,  and  it  has  never  been 
claimed  that  the  ordinary  stone-block  pavement  with  its  wide- 
and  permeable  joints  was  specially  unhealthy.  It  has  not  been 
proved  that  wood  pavements  appreciably  affect  the  health 
of  a  community. 

Continuous  sheet  pavements  are  best  in  sanitary  qualities,, 
although  block  pavements  having  joints  filled  with  tar  or  hy- 
draulic cement  are  not  seriously  objectionable. 

894.  Freedom  from  Dust  and  Mud.  The  materials  of  an 
ideal  pavement  should  not  grind  up  and  make  dust  in  dry 
weather  or  mud  in  wet  weather.  The  dust  and  mud  not  only 
add  to  the  expense  of  cleaning  the  pavement,  but  are  a  discom- 
fort to  those  who  use  the  pavement  and  to  those  who  live  or  do 
business  adjacent  to  it. 

895.  Comfort  in  Use.  If  the  pavement  is  to  be  used  for 
pleasure  driving,  the  comfort  of  the  users  must  be  considered; 


SELECTING   THE   BEST   PAVEMENT.  581 

and  therefore  the  pavement  should  have  a  smooth  surface 
which  is  free  from  dust  when  it  is  dry  and  from  mud  when  it 
is  wet. 

896.  Temperature  of  Pavements.  During  hot  weathe^ 
there  is  frequently  complaint  that  one  pavement  reflects  or 
radiates  more  heat  than  another.  Observations  made  in 
Washington,  D.  C,  when  the  temperature  of  the  air  2  feet 
above  the  pavement  was  104°  F.,  showed  the  temperature 
of  three  pavements  to  be  as  follows:  artificial  sheet  asphalt 
140°,  asphalt  block  122°,  and  macadam  118°.*  Observations 
in  Boston,  when  the  temperature  of  the  air  in  the  shade  was 
98°  F.,  gave  the  temperature  of  four  pavements  as  follows: 
wood  block  124£°,  granite  block  115°,  sheet  asphalt  113°,  and 
macadam  102^°.  The  observations  are  not  conclusive  as  to 
the  relative  temperatures  of  different  pavements,  but  show  that 
there  is  no  very  great  difference  between  the  several  kinds.  The 
temperature  of  the  pavement  depends  upon  its  color,  which 
varies  with  the  material. 

897.  Selecting  the  Best  Pavement.  The  problem  of  se- 
lecting the  best  pavement  for  any  particular  case  is  a  local  one, 
not  only  for  each  city  but  also  for  each  of  the  various  parts  into 
which  the  city  is  imperceptibly  divided,  and  it  involves  so  many 
elements  that  the  nicest  balancing  of  the  relative  values  for  each 
kind  of  pavement  is  required  to  arrive  at  a  correct  conclusion. 

In  some  localities,  the  proximity  of  one  or  more  paving 
materials  determines  the  character  of  the  pavement,  while  in 
other  cases  it  may  require  a  careful  investigation  to  select  the 
most  suitable  material.  Local  conditions  should  always  be 
considered,  and  hence  it  is  not  possible  to  lay  down  any  fixed 
rule  as  to  what  material  makes  the  best  pavement;  but  a  careful 
study  of  the  requirements  of  the  ideal  pavement  and  of  the 
qualities  of  the  different  kinds  of  pavements  will  promote  an 
intelligent  selection  in  any  particular  case.  The  decision  must 
always  be  largely  a  matter  of  judgment;  but  the  engineer 
should  reach  his  conclusion  by  a  series  of  carefully  considered 
steps,  and  not  by  a  single  hap-hazard  leap.     He  should  weigh 

*  Proc.  Amer.  Soc.  Municipal  Improvements,  Vol.  5,  p.  161. 


582  COMPARISONS   OF   PAVEMENTS.  [CHAP.  XVIIL 


all  the  evidence  and  not  base  a  decision  upon  a  single  item,  as 
is  too  often  the  case;  nor  should  he  adopt  the  practice  of  some 
other  locality  without  a  careful  consideration  of  the  local  re- 
sources and  of  the  needs  of  the  place  in  which  the  pavement  is 
to  be  laid,  as  is  frequently  done. 

898.  Relative  Merits.  It  is  proposed  to  compare  different  kinds 
of  pavements  by  assigning  percentages  to  the  different  qualities  of 
an  ideal  pavement,  and  then  with  this  as  a  guide  to  assign 
numerical  values  to  the  various  qualities  of  the  several  kinds  of 
pavements. 

The  various  qualities  of  a  perfect  pavement  have  been  dis- 
cussed in  §  877  to  §  896,  and  these  qualities  have  been  grouped 
in  Table  61,  page  583,  under  the  three  heads:  (1)  economic 
qualities,  (2)  sanitary  qualities,  and  (3)  acceptability.  Oppo- 
site each  of  these  qualities  in  the  first  column  of  Table  61  is 
placed  a  number  which  is  believed  to  represent  the  average  rela- 
tive importance  of  that  particular  quality  on  a  scale  of  100. 

The  assignment  of  these  numbers  is  wholly  a  matter  of 
judgment,  and  different  individuals  will  differ  greatly  as  to  the 
relative  values  to  be  given  to  each  quality ;  but  the  table  is  only 
to  show  a  method  whereby  the  good  and  the  bad  qualities 
of  one  kind  of  pavement  may  be  balanced  against  those  of 
another  kind,  and  a  conclusion  may  be  reached  step  by  step, 
which  represents  the  algebraic  sum  of  the  judgment  on  each  item. 

Different  values  should  be  assigned  to  the  same  quality 
according  to  the  attendant  conditions.  If  the  street  is  in  a 
manufacturing  district  and  subject  to  heavy  traffic,  ease  of  trac- 
tion should  be  assigned  a  comparatively  high  value,  and  noise 
a  very  low  value.  For  an  office  district,  quietness  is  the  con- 
trolling factor,  and  should  therefore  have  a  relatively  high 
value.  Similarly,  for  a  residence  district  with  its  light  driving, 
healthfulness  and  freedom  from  dirt  and  dust  may  be  the  most 
important  element;  for  a  residence  district  where  the  property 
owners  can  not  afford  an  expensive  pavement,  the  first  cost 
may  determine  the  kind  of  pavement;  and  on  a  steep  grade 
slipperiness  may  out-weigh  all  other  conditions  in  determining 
the  kind  of  pavement  to  be  employed.  The  application  of 
these  principles  is  likely  to  be  complicated  by  the  personal 
interests  of  the  residents  or  property  holders,  since   opinions 


SELECTING    THE   BEST   PAVEMENT. 


583 


TABLE  61. 

Relative  Values  of  the  Different  Qualities  of 

Various  Pavements. 


Qualities. 

Percentage  Assigned 

to  the  Quality. 

d 

i 

S 

•a  ® 
SB 

»-i  > 

"S"3 

•O  ft 

W.  m 
< 

6 

|| 

M  ° 

fflo 

d 

0 

0) 

► 

E 

o 

S 

1 

CQ  B 

"   Q 

C  S 

So 
S  5 

0,0 

i 

Economic  Qualities: 

Low  first  cost 

15 
20 
10 
5 
10 

6 

16 
10 

2 
10 

9 
14 
8 
4 
9 

15 
6 
5 
5 

1 

10 
8 
6 
5 
3 

3 
20 
3 
3 
6 

8 

2 
3 

Low  cost  of  maintenance 

Ease  of  traction 

12 

7 

4 

Good  foot  hold 

1 

5 

Ease  of  cleaning 

9 

Total 

60 

15 
10 

44 

10 
10 

44 

7 
8 

32 

15 
6 

32 

15 
6 

35 

2 

7 

37 

6 

Sanitary  Qualities: 

Noiselessness 

13 

7 

Healthfulness 

5 

Total 

25 

10 
3 
2 

20 

10 
2 
1 

15 

9 

1 
1 

21 

1 
3 
2 

21 

3 
3 
2 

9 

8 
0 

1 

18 

8 
q 

Acceptability: 

Free  from  dust  and  mud 

Comfortable  to  use 

7 
2 

10 

Non-absorbent  of  heat 

1 

Total 

15 
100 

13 

77 

11 

70 

6 
59 

8 
61 

9 
53 

10 

Grand  total 

65 

are  likely  to  differ  according  to  whether  the  point  of  view  is  that 
of  a  tenant,  a  resident  property-holder  or  a  non-resident  prop- 
erty-holder. 

899.  Each  quality  of  a  pavement  will  now  be  considered, 
and  the  degree  of  perfection  of  this  quality  possessed  by  each 
kind  of  pavement  will  be  indicated  by  a  numerical  value. 

900.  Importance  of  First  Cost.  Since  the  cost  of  a  pave- 
ment varies  greatly  with  local  conditions,  it  is  not  possible  to 
state  a  general  value  for  the  cost  of  each  kind;  but  for  the  sake 
of  illustration,  the  values  in  the  exhibit  below  will  be  assumed, 
which  values  are  believed  to  be  roughly  approximate  averages 
for  the  best  of  each  "kind  of  pavement. 


584  COMPAEISONS   OF   PAVEMENTS.  [CHAP.   XVIII. 

Kinds  of  Pavement.                        Cost  per  Sq.  Yd.  Relative  Weight. 

Gravel $0.50     , 15 

Macadam 0.75 10 

Brick 1 .75     9 

Rectangular  Wood  Block 2.00     8 

Sheet  Asphalt 2.75     6 

Granite  Block 3.50     3 

The  last  column  of  the  above  exhibit  shows  the  relative  weights 
assigned  to  the  quality  of  cheapness.  Since  gravel  is  the  lowest 
in  first  cost,  it  possesses  the  quality  of  cheapness  in  the  highest 
degree;  and  consequently  it  is  given  a  weight  of  15 — the  value 
assigned  to  the  ideal  pavement  in  Table  61.  The  weights 
assigned  to  this  quality  decrease  from  gravel,  the  cheapest,  to 
granite  block,  the  most  expensive.  The  several  weights  assigned 
above  to  low  first  cost  are  entered  opposite  this  quality  in 
Table  61. 

901.  The  first  cost  of  a  pavement  not  infrequently  has  undue 
weight  in  comparing  the  relative  merits  of  different  kinds  of 
pavements.  In  this  connection  the  fact  should  not  be  over- 
looked that  all  the  other  expenses  connected  with  a  pavement — 
cost  of  maintaining  and  cleaning  it,  of  conducting  transporta- 
tion over  it,  of  wear  and  tear  on  vehicles  and  horses — is  a  con- 
tinuing expense,  while  the  cost  of  construction  is  incurred  once 
for  all;  and  therefore  in  comparing  the  economic  value  of 
pavements,  it  is  only  the  annual  interest  on  the  cost  of  construc- 
tion that  should  be  considered  in  connection  with  the  other 
items  of  annual  expense.  The  pavement  which  costs  the  most 
to  construct  is  not  always  the  most  expensive,  nor  is  the  one 
lowest  in  the  first  cost  always  the  cheapest  in  the  end.  The 
pavement  which  is  truly  the  cheapest  is  the  one  which  gives 
the  most  profitable  returns  in  proportion  to  the  amount  which 
is  expended  upon  it,  as  will  be  shown  under  Cost  of  Mainte- 
nance in  §  902. 

A  pavement  is  sometimes  selected  because  of  its  low 
first  cost,  for  other  than  economic  reasons.  Often  the  cost  of 
construction  is  charged  against  the  abutting  property,  while 
maintenance  is  paid  for  by  the  whole  city;  and  the  result  is  that 
many  property  owners  prefer  a  cheap  pavement  because  they 
must  pay  for  it,  notwithstanding  the  fact  that  the   cheaper 


SELECTING    THE    BEST   PAVEMENT. 


585 


pavement  may  cost  more  for  maintenance  and  be  dearer  in  the 
long  run.  Again,  the  property  holders  are  sometimes  really  unable 
to  pay  for  the  most  economical  pavement,  and  hence  a  pavement 
low  in  first  cost  is  selected  as  a  temporary  expedient. 

902.  Importance  of  Annual  Cost.  Since  there  are  no  accurate 
data  concerning  the  volume  of  traffic  and  the  wear  of  pavements, 
and  since  only  a  few  cities  keep  account  of  the  amount  spent 
upon  a  particular  pavement  or  even  upon  a  particular  kind  of 
pavements,  it  is  impossible  to  make  any  reliable  comparisons 
of  the  cost  of  maintenance  of  different  pavements.  With  the 
present  state  of  our  knowledge,  all  that  can  be  done  is  to  make 
an  estimate  of  the  life  of  the  pavement  under  the  particular 
traffic,  and  then  deduce  the  annual  cost,  which  includes  the  interest 
upon  the  first  cost  and  the  expenditures  for  repairs  including 
periodical  renewals.     See  §  885. 

Table  62  shows  the  estimate  of  the  annual  cost  of  several 
kinds  of  pavements  for  Minneapolis,  Minn.*  The  computations 
are  made  for  a  term  of  20  years  for  a  street  having  an  estimated 
daily  traffic  of  150  tons  per  foot  of  width.  The  original  table  did 
not  contain  the  last  column,  which  is  here  added  by  obvious  com- 
putations. 

TABLE  62. 
Estimated  Annual  Cost  of  Various  Pavements  in  Minneapolis,  Minn. 


4 

Kind  of  Pavement. 

073 

Si* 

~a 

n 

£6- 

5 

O 

¥ 

-*> 

Value  of  the 

Pavement  at  the 

End  of  20  Years, 

per  Sq.  Yd. 

P  C  fc" 

Is 

1 

Cedar,  2-inch  plank  foundation 

$0.85 

1.45 
1.S8 
2.75 
1.80 
1.90 
2  15 
2.70 

$0.79 

.74 
1.88 

6 

S 
20 

|  of  $0.79  =  $0.53 
i  of  $0.74  4-  con- 
crete =  $1.04 
$0.60 
2.00 
.80 
.80 
.80 
.80 

$0.22 

.25 
.22 
.32 
.29 
.31 
.36 
.48 

$0.18 

2 

3 

4 

"        concrete  foundation  with 

tar 

Granite 

Asphalt    Trinidad  Lake 

B-  .ck   small  size  Minnesota..  .    . 

"         large  s^e  Minnesota 

"        from  Galesburg  fill 

.18 
.13 

.18 

5 
6 

7 

8 

1.13 

1.23 
1.48 
2.03 

10 
10 
10 
10 

.20 
.21 
.25 
.34 

*  Annual  Report  of  City  Engineer  F.  W.  Cappelen  for  1893,  p.  19. 

f  Kept  in  repair  for  ten  years,  after  which  add  eight  cents  per  yard  per  year, 

J  All-rail  rate  for  freight. 


586 


COMPARISONS   OF   PAVEMENTS.  [CHAP.   XVIII. 


903.  Table  63  gives  similar  results  for  pavements  in  Chicago, 
by  a  paving  expert.*  Interest  in  this  example  is  computed 
at  6  per  cent. 

TABLE  63. 
Estimated  Annual  Cost  of  Various  Pavements  in  Chicago,  III. 


i 

i 

Kinds  of  Pavement. 

a 
.2 

O     . 

■ 

t 

q 
O 

05 

IS 

an-* 
c    . 
u  cr 

O  « 
l 

Life  of  Pave- 
ment Under 
Different 
Classes  of 
Traffic, 
i       in  Years. 

Annual  Cost  of 
Maintenance  for 

a  Term  of  50 
Years, 

per  Sq.  Yd. 

1  . 

- 

1  io 

1   12 

|12' 

'  30* 

!  35 

!   35 

35 

'is' 

i  50 

I  50 

i'io' 

i 

'■3 

7 

8 

9 

9 

10 

15 

20 

20 

20 

25 

8 

30 

25 

15 

6 

0) 

"4 

5 

i2' 

12 
10 
15 

15' 

12 
8 

B 

3 

1 

2 

Cedar  block  on  2-inch  plank 

"        "    6"  of  rubble 

$1.00 
1.25 
1.40 
1.40 
1.65 
1.45 
1.60 
1.95 
1.60 
1.85 
3.00 
3.50 
3.15 
0.90 
1.35 

$0.90 
0.80 
0.80 
0.80 
0.80 
1.15 
1.15 
1.15 
1.15 
1.15 
2.00 
2.00 
2.00 
0.70 
0.75 

$0.22 
0.20 

6!20 

o'.u 

0.14 
0.13 
0.13 

'6!44 

0.21 
0.20 

'6.23 

?0.33 
0.28 
0.28 
0.28 
0.26 
0.24 
0.20 
0.19 
0.19 
0.17 
0.69 
0.30 
0  29 
0.15 
0.35 

8 

•I                  ..        Q,      M              .. 

6.53 

4 
5 
6 
7 
8 
9 
10 

11 

"          "        "    6"  "  concrete 

9"  "       "          

Brick,  1  course  on  6"  of  rubble 

1  "          "   9"  "       "        

2  "         "    6"  "       *'        

"         1     "         "    6"  *'  concrete  .... 

1     «'         "    9"  "       " 
Sheet  asphalt  on  6"  of  concrete 

0A& 

6'.27 
0.27 
0.33 
0.25 

6  47 

13 

l-i 

"          "    6"  of  rubble 

0.50 
0  23 

18 

Macadam,  granite  top  dressing 

904.  Table  64,  page  587,  gives  the  estimated  average  cost 
of  several  kinds  of  pavements,  computed  upon  a  little  different 
basis  than  the  two  preceding  tables,  by  a  man  having  wide 
experience  in  paving  matters. f 

"  The  data  assumed  in  computing  this  table  may  be  regarded 
as  fair  averages  for  pavements  located  in  cities  in  the  Mississippi 
Valley,  on  streets  having  a  traffic  of  about  33  tons  per  day  per 
foot  of  width.  The  tonnage  assumed  corresponds  to  that  on 
a  rather  heavily  traveled  residence  street,  or  a  business  street 
of  medium  travel,  in  cities  of  100,000  to  200,000  population, 
and  the  result  might  be  entirely  different  for  a.  street  hav- 
ing a  larger  or  a  smaller  volume  of  travel.  The  interest  in 
the  table  includes  that  on  the  cost  of  construction  and  on  the 
annual  expense  for  repairs,  the  latter  being  computed  on  the 
assumption  that  this  expense  is  uniformly  distributed  over  the 
last  two  thirds  of  the  life  of  the  pavement." 

*  D.  W.  Mead,  in  Jour.  Assoc.  Eng'g  Societies,  Vol.  11,  p.  589. 

f  S.  Whinery,  in  Trans.  Assoc.  Civil  Eng  rs  of  Cornell  University,  1900,  p.  100. 


SELECTING   THE   BEST   PAVEMENT. 


587 


TABLE  64. 

Estimated  Average  Annual  Cost  of  Various  Pavements  in  Cities 
op  the  Mississippi  Valley. 


d 

Items  of  Expense. 

M   . 

g   <B 

h 

M 

Q 

«  a 

'2  a 
c 

O 

< 

0> 

CQ 

Si 

•SI 

•fi  (3 

pa  o 

u 

PQ 

M  d 
1  d 

M 

o    . 
£•0 

mi 

uW 

3g 

■ 

a 

O 
XI 

o 
Q 

a 

a 
1 

i 

2 
3 

Cost  of  construction 

Annual  cost  of  repairs 

Interest  at  6  per  cent 

$3.75 

.40 

4.66 

$3.20 

.60 

3.06 

$2.40 

.50 

2.31 

$2.15 

.45 

1.66 

$1.50 
.48 
.80 

$1.80 
.36 
.69 

$1.15 
.30 
.31 

$1.00 
.48 
.54 

$1.20 

1.00 

.46 

4 

8.81 
.76 

6.86 
.18 

5.21 
.72 

4.26 
.78 

2.78 
.14 

2.85 
.48 

1.76 
.12 

2.02 
.10 

2.66 

5 

Value  of  old  pavement 

.10 

6 

8.05 
20 
$0.40 
0.25 

6.68 

15 
$0.44 

0.24 

4.46 

15 
$0.30 

0.19 

3.48 

12 
$0.29 

0.18 

2.64 

8 
$0.33 

0.16 

2.07 

6 

$0.34 

0.12 

•  1.64 

4 
$0.41 

0.15 

1.92 

8 
$0.24 

0.13 

2.56 

7 

Estimated  life  of  pavement. 

5 

8 
9 

Total  cost  per  year.  .  .  . 
Net  cost  per  year 

$0.51 
0.29 

The  original  table  gives  only  the  total  average  annual  cost 
of  the  several  pavements  during  their  estimated  life,  i.  e.,  the 
original  table  ends  with  the  eighth  line  of  Table  64;  and  the 
ninth  line  was  computed  as  follows:  The  difference  between 
the  cost  of  construction  and  the  value  of  the  old  pavements  was 
divided  by  the  number  of  years  representing  the  estimated  life 
of  the  pavement,  and  the  quotient  was  subtracted  from  the 
total  cost  per  year. 

905.  An  examination  of  the  three  preceding  tables  shows 
that  the  life  of  the  pavement,  or  the  cost  of  perpetual  mainte- 
nance, is  the*  most  important  matter  in  comparing  the  relative 
economy  of  two  or  more  pavements.  The  estimated  relative 
degree  in  which  the  several  pavements  in  Table  61  possess  the 
desirable  quality  of  low  cost  of  maintenance  is  shown  by  the 
percentages  in  line  2  of  that  table. 

906.  Value  of  Ease  of  Traction.  Under  this  may  be  included 
not  only  the  power  required  to  move  loads  but  also  the  con- 
sequential damages  to  vehicles,  since  they  both  vary  with  the 
roughness  of  the  pavement.  From  a  study  of  the  results  in 
Table  9,  page  31,  the  weights  are  assigned  to  this  quality  for 
the  different  kinds  of  pavements,  as  shown  in  Table  61. 


588  COMPARISONS   OF   PAVEMENTS.  [CHAP.  XVIII. 

907.  Value  of  Foothold.  From  a  study  of  §  887,  the  relative 
degree  of  slipperiness  is  stated  in  numbers  and  entered  in  Table  61. 
If  the  pavement  is  to  be  upon  a  steep  grade,  this  quality  may  be 
a  controlling  factor. 

908  Importance  of  Ease  of  Cleaning.  The  relative  ease  with 
which  certain  types  of  pavements  may  be  swept,  as  determined  by 
the  cost  of  doing  the  work  in  New  York  city,  is  as  follows:  asphalt, 
100;  brick,  100;  rectangular  hard-wood  blocks,  100;  granite  blocks, 
150;  Belgian  blocks,  160;  cobble  stones,  400.*  For  sanitary 
reasons,  New  York  city  has  spent  a  million  dollars  a  year  for 
the  past  few  years  in  substituting  sheet  asphalt  pavements 
for  stone  block  in  the  congested  tenement  districts,  chiefly  on 
account  of  the  greater  ease  with  which  the  asphalt  is  kept  clean. 

The  cost  of  sweeping  ordinary  stone  block,  round  wrood 
block,  and  brick  with  sand  filler  usually  ranges  between  40 
and  48  cents  per  1,000  square  yards  for  each  sweeping,  and 
sheet  asphalt  from  30  to  38  cents,  depending  upon  the  thor- 
oughness of  doing  the  work,  the  frequency  of  sweepings,  the 
kind  of  business  in  the  property  adjoining,  and  the  amount  of 
the  traffic.  The  relative  weight  to  be  assigned  to  this  item  will 
vary  with  the  frequency  of  cleaning. 

The  estimated  weight  to  be  assigned  to  the  several  pavements 
on  account  of  their  ease  of  cleaning  is  entered  in  Table  61,  page 
583. 

909.  Value  for  Other  Qualities.  From  a  consideration  of  the 
discussion  in  §  892-96,  the  percentages  for  the  other  qualities  are 
inserted  in  TaWe  61. 

910.  Conclusion.  The  totals  at  the  foot  of  Table  61,  page 
583,  represent  the  summation  of  the  individual  decisions  on  the 
several  qualities,  and  the  larger  the  total  the  more  desirable  the 
pavement.  The  particular  results  in  this  example  may  not  be 
applicable  to  any  locality,  and  each  person  will  have  his  own  opin- 
ion as  to  the  merits  and  defects  of  any  particular  pavement;  but 
the  method  of  analysis  is  applicable  to  any  particular  case,  and 
will  enable  the  engineer  intelligently  and  unerringly  to  reach  the 


*  Street  Cleaning  in  New  York  City  in  1895-97,  p.  157— Supplement  to  Vol.  II.  of 
Municipal  Affairs.     New  York,  1898. 


SELECTING   THE   BEST   PAVEMENT.  589 

final  conclusion  to  which  his  opinion  in  detail  leads.  The  above 
method  has  something  of  the  mathematical  form,  but  the  fact 
should  not  be  forgotten  that  it  is  based  upon  judgment  and  that 
therefore  it  can  not  be  expected  to  give  results  of  a  high  degree 
of  accuracy. 

In  practice  the  application  of  this  method  is  much  less  com- 
plicated than  appears  from  the  above  example,  for  usually  prox- 
imity of  some  natural  pavement  materials  or  freight  rates  on  others, 
limits  the  choice  to  a  comparatively  few  kinds  of  pavements. 
Further,  the  decision  as  to  the  kind  of  pavement  to  be  laid  is  often 
influenced  by  the  fancy  or  ability  of  those  who  pay  for  it.  How- 
ever, the  engineer  should  employ  a  logical  process  in  arriving  at 
his  own  conclusions,  and  thus  be  in  a  position  to  give  sound  advice 
upon  the  economic  principles  involved. 


CHAPTER  XIX. 
SIDEWALKS. 

912.  Sidewalk  is  the  term  ordinarily  applied  to  the  foot- way 
pavements  usually  placed  on  each  side  of  the  carriage-way  pave- 
ments; and  will  be  here  employed  to  include  also  foot-way  pave- 
ments in  public  parks  and  private  grounds. 

913.  LOCATION.  On  business  streets  the  sidewalk  usually 
extends  from  the  building  line  to  the  curb ;  but  on  residence  streets 
the  sidewalk  is  usually  not  so  wide  as  the  space  from  the  property 
line  to  the  curb,  and  hence  there  is  a  choice  as  to  its  location. 
The  inner  edge  of  the  walk  is  usually  placed  about  a  foot  from  the 
property  line  or  from  the  line  marking  the  limit  of  steps,  areaways, 
courtyards,  etc.,  a  grass  plat  intervening  between  the  walk  and 
the  curb,  but  in  a  few  cases  the  outer  edge  of  the  walk  is  placed 
next  to  the  curb.  The  former  position  is  more  satisfactory  than  the 
latter,  since  pedestrians  are  further  removed  from  the  dust  and 
dirt  of  the  street,  from  the  street  sprinkler,  and  from  horses  tied 
at  the  curb,  and  are  better  protected  from  street  traffic,  which  is 
an  important  matter  in  the  case  of  children.  Further,  if  the  side- 
walk is  next  to  the  curb,  the  trees  either  are  further  removed  from 
the  pavement  and  consequently  do  not  give  as  good  an  appearance 
to  the  street  and  are  likely  to  shut  out  light  and  air  from  the  abut- 
ting houses,  or  are  planted  in  notches  or  pockets  left  in  the  side- 
walk, a  method  which  reduces  the  available  width  of  the  walk  and 
mars  its  symmetry.  The  only  advantage  claimed  for  the  sidewalk 
next  to  the  curb  is  that  the  yards  are  thereby  virtually  enlarged; 
but  the  grass  plat  is  practically  as  valuable  between  the  walk  and 
the  curb  as  between  the  walk  and  the  property  line.  The  sidewalk 
next  to  the  curb  appears  to  be  the  practice  in  Washington,  D.  C. 

590 


WIDTH — TRxVXSVERSE    SLOPE — GRADE.  591 


914.  WIDTH.  On  residence  streets  in  small  cities,  the  walk  is 
usually  4  to  6  feet  wide ;  and  on  streets  solidly  built  up  with  houses 
several  stories  high,  the  walk  is  8  or  10  feet  wide,  unless  the  street 
is  a  thoroughfare  or  a  promenade,  in  which  case  the  width  of  the 
walk  is  greater.  In  Washington  the  walk  on  each  side  of  the  car- 
riage-way pavement  is  about  15  per  cent  of  the  width  of  the 
narrower  streets  and  about  10  per  cent  of  the  wide  avenues;  and 
in  Chicago  the  sidewalk  is  roughly  about  20  per  cent  of  the 
width  of  the  street,  except  for  streets  under  50  feet  wide  where  it 
is  about  15  per  cent. 

A  number  of  the  states  provide  by  law  for  a  sidewalk  space  on 
either  side  of  the  road,  "where  possible,"  equal  in  width  to  one 
tenth  of  the  right  of  way,  and  make  it  a  misdemeanor  to  ride 
or  drive  horses  upon  this  space.  Many,  perhaps  most,  of  the 
rural  roads  of  Europe  have  a  well-paved  sidewalk  on  one  side  and 
rows  of  trees  upon  both  sides;  but  in  this  country  there  are  almost 
no  artificial  foot-paths  upon  the  side  of  rural  roads. 

915.  TRANSVERSE  SLOPE.  The  surface  of  sidewalks  should 
slope  from  the  property  toward  the  curb,  to  shed  rain  water  toward 
the  gutter.  This  transverse  slope  varies  from  1  inch  in  3  feet  to 
1  inch  in  5  feet,  the  former  for  the  rougher  walks,  as  brick,  and 
the  latter  for  the  smoother  ones,  as  asphalt  and  cement. 

If  the  walk  is  on  the  side  of  a  street,  it  should  have  a  uniform 
slope  toward  the  center  of  the  street;  but  if  it  is  in  a  park,  the 
surface  should  have  sufficient  crown  to  shed  the  water  to  the  sides 
and  to  keep  the  surface  free  from  standing  water.  This  crown 
should  be  no  more  than  is  required  to  drain  the  surface,  since  an 
excess  causes  traffic  to  keep  in  the  center  of  the  walk.  The  crown 
in  any  particular  case  will  depend  upon  the  material  employed 
for  the  surface  and  will  be  discussed  in  subsequent  sections. 

The  lower  edge  of  a  sidewalk  should  be  sufficiently  above  the 
surface  of  the  adjoining  ground  to  give  perfect  drainage  to  the 
surface.  In  public  parks  and  private  grounds  the  surface  of  the 
walk  should  be  2  or  3  inches  above  the  general  level  of  the  ground, 
in  order  that  the  walk  may  not  become  a  drainage  channel. 

916.  GRADE.  The  longitudinal  slope  of  the  sidewalk  must 
conform,  at  least  approximately,  to  the  grade  of  the  street;  and 
ordinarily  if  vehicles  can  use  the  carriage-way  pavement,  pedes- 


SIDEWALKS. 


[CHAP.   XIX. 


trians  can  use  the  sidewalk,  unless  it  is  proportionally  consider- 
ably smoother  than  the  carriage-way  pavement,  in  which  case  the 
sidewalk  may  be  built  in  sections  having  flatter  grades  with  one 
or  more  steps  between  the  sections. 

In  considering  whether  or  not  to  cut  down  a  hill  or  to  fill  up  a 
hollow  to  decrease  the  rise  and  fall  (§  66)  of  the  sidewalk,  it  is  well 
to  remember  that,  measured  by  the  energy  expended  by  a  pedes- 
trian, a  rise  of  1  foot  is  equivalent  to  a  horizontal  distance  of  about 
18  feet  (see  foot-note  on  page  58). 

917.  Sidewalk  across  Private  Driveway.  Very  often  the 
driveway  from  the  street  across  the  sidewalk  to  gates  or  into  build- 
ings is  constructed  with  an  offset  of  from  2  to  6  inches"  where  the 
walk  meets  the   driveway,  as   shown   in   Fig.  146.     This  depres- 


Fig.  143. — Depressed  Driveway  across 
Walk. 


Fig.  147 — Proper  Driveway  across 
Walk. 


sion  is  often  unseen  by  a  pedestrian  until  he  steps  into  it  with  a 
a  sudden  jolt.  The  depression  detracts  from  the  symmetrical 
appearance  of  the  walk,  and  is  an  entirely  needless  source  of 
danger.  Fig.  147  shows  a  much  better  and  also  a  cheaper  arrange- 
ment. When  it  is  necessary  to  provide  for  surface  drainage  from 
the  private  property,  the  driveway  may  be  paved  with  an  almost 
imperceptible  depression  in  the  center  which  will  conduct  the 
water  into  the  gutter. 

918.  MATERIAL.  Sidewalks  are  constructed  of  asphalt,  brick, 
hydraulic  cement  concrete,  cinders,  gravel,  macadam,  plank,  stone 
slabs,  and  tar  concrete.  The  method  of  construction  for  each  of 
these  materials  will  be  considered  separately  in  the  above  (alpha- 
betical) order. 

919.  ASPHALT  WALKS.  Asphalt  is  used  for  sidewalks  both 
in  the  form  of  a  monolithic  sheet  and  in  blocks  or  tiles,  in  much 


BRICK    SIDEWALKS.  593 


the  same  way  as  for  carriage-way  pavements,  except  that  the 
foundation  need  not  be  so  strong  nor  the  wearing  coat  so  thick. 

920.  Sheet  Asphalt.  The  material  for  the  wearing  coat  of 
artificial  sheet  asphalt  foot-way  pavements  may  be  mixed  softer 
than  for  carriage-way  pavements,  as  the  former  are  not  required 
to  bear  the  heavy  loads  of  the  latter.  The  softer  the  mixture  the 
greater  its  life,  since  the  greater  the  amount  of  oil  the  longer  the 
time  before  the  pavement  will  be  rendered  brittle  by  the  effect  of 
volatilization  and  oxidation.  Asphalt  is  unsuitable  for  unfre- 
quented Walks,  since  cracks  due  to  expansion  and  contraction  are 
not  re-cemented  by  the  pressure  of  traffic  (§  654).  Monolithic 
asphalt  foot-way  pavements  are  not  common  in  this  country,  the 
only  city  in  which  they  are  used  to  any  considerable  extent  being 
Washington,  D.  C,  where  the  material  removed  from  old  asphalt 
carriage-way  pavements  in  making  repairs  and  in  re-surfacing  is  used 
for  foot-ways.  .  Such  pavements  with  a  3-inch  hydraulic-cement 
concrete  base  and  a  1-inch  wearing  coat  usually  cost,  exclusive  of 
grading,  from  90  cents  to  $1.00  per  square  yard. 

Sheet  asphalt  foot-way  pavements  are  used  to  a  considerable 
extent  in  European  cities,  particularly  in  Paris.  They  are  made  of 
asphalt  mastic  or,  in  French,  asphalte  coule,  which  consists  of  an  as- 
phaltic  limestone  to  which  has  been  added  some  asphalt,  usually 
that  from  Trinidad.  The  material  is  heated  and  carried  to  the 
walk  in  buckets,  and  being  of  a  consistency  to  flow  slowly  is  poured 
out  upon  the  foundation  and  spread  to  the  desired  thickness, 
usually  about  f  of  an  inch,  and  smoothed  with  wooden  floats. 
Some  coarse  sand  is  usually  rubbed  into  the  surface  to  keep  it  from 
being  slippery.     When  cool  the  pavement  is  ready  for  use. 

921.  Asphalt  Tiles.  Asphalt  sidewalk-paving  tiles  are  made 
2\  inches  thick  having  a  top  surface  8  inches  square  or  a  hexagon 
of  the  same  area.  For  a  description  of  the  composition  of  the 
blocks  and  of  the  method  of  making  them,  see  Art.  4,  Chapter 
XIII,  page  447.  The  blocks,  or  tiles  as  they  are  commonly 
called,  are  laid  substantially  as  described  for  asphalt  block  carriage- 
way pavements — see  §  682-91. 

922.  BRICK  SIDEWALKS.  Brick  sidewalks  are  very  common, 
and  when  properly  constructed  are  cheap,  durable,  and  reasonably 
satisfactory.     Commonly   they    consist    of   ordinary   hard-burned 


594  SIDEWALKS.  [CHAP.   XIX. 

building  brick  laid  flatwise  upon  a  porous  bed  of  sand  or  cinders, 
although  occasionally  in  heavily  traveled  business  districts  the 
bricks  are  set  on  edge  and  the  joints  are  filled  with  cement  mortar. 

923.  Foundation.  If  the  soil  is  a  very  retentive  clay,  or  if  the 
foundation  is  not  well  drained,  the  foundation  should  be  excavated 
to  a  depth  of  10  inches;  but  if  the  soil  is  an  ordinary  loam,  l  depth 
of  8  inches  is  sufficient.  All  loose  or  spongy  material  should  be 
removed;  and  the  subgrade  should  be  formed  parallel  to  the 
surface  of  the  finished  walk. 

Upon  the  subgrade  should  be  spread  a  layer  of  clean  coarse 
sand  or  fine  gravel  or  cinders,  to  furnish  a  firm  unyielding  support 
for  the  bricks.  If  laid  upon  a  foundation  that  became  plastic 
when  wet,  the  bricks  would  work  down  into  the  foundation  and 
the  mud  would  work  up  between  the  bricks,  thus  making  the  walk 
temporarily  muddy  and  permanently  rough.  Whatever  the 
material  employed  for  the  foundation,  it  should  be  thoroughly 
consolidated  by  tamping  or  rolling;  and  if  cinders  are  used,  par- 
ticular care  should  be  given  to  the  tamping,  so  that  the  larger 
clinkers  shall  be  broken  up  and  the  finer  particles  be  worked  in 
around  the  coarser  pieces.  A  thorough  flooding  is  beneficial'  in 
consolidating  cinders,  as  the  water  aids  in  working  the  fine  material 
into  the  interstices  between  the  larger  pieces.  If  flooded  and  well 
tamped,  cinders  will  consolidate  to  about  three  fourths  of  their 
thickness  when  loose.  Cinders  containing  fine  ashes  are  undesir- 
able for  sidewalk  foundations,  since  it  is  difficult  to  consolidate 
them,  and  since  the  ashes  are  likely  to  be  washed  to  the  bottom 
by  rains  and  thereby  to  cause  the  surface  of  the  sidewalk  to 
settle.  Cinders  made  by  steam  plants,  sometimes  called  steam 
ashes,  are  better  for  this  purpose  than  are  household  ashes,  since 
the  fires  in  the  former  are  hotter  and  fuse  most  of  the  ashes  into 
cinders,  leaving  little  or  no  fine  material.  Steam  cinders  that 
have  been  drenched  with  water  as  soon  as  drawn  from  the  furnace, 
usually  called  black  cinders,  are  better  than  those  that  have  been 
allowed  to  burn  in  the  pile,  since  they  contain  fewer  fine  ashes. 
Wood  ashes  are  very  objectionable,  since  they  contain  a  great 
deal  of  fine  material,  and  since  a  considerable  part  is  soluble  and 
will  wash  entirely  away  thus  allowing  the  surface  to  settle. 

Upon  the  foundation  of  gravel  or  cinders  should  be  placed  a 


BRICK    SIDEWALKS. 


595 


layer  of  sand  H  or  2  inches  deep  to  serve  as  a  cushion  upon  which 
to  lay  the  bricks  (see  §  761). 

924.  The  Bricks.  The  bricks  should  be  hard-burned  and  have 
plane  parallel  surfaces  and  sharp  right-angled  edges.  They  should 
give  a  clear  ringing  sound  when  two  are  struck  together,  and  when 
broken  should  show  a  compact  uniform  structure  free  from  air 
bubbles  and  cracks.  They  need  not  be  burned  as  hard  as  is  re- 
quired for  carriage-way  pavements  (§  723);  but  they  should  be 
equally  as  Carefully  sebcted  to  secure  a  uniform  quality  and 
thereby  insure  uniform  wear.  Most  sidewalks  are  made  of  hard- 
burned  ordinary  building  bricks;  but  sometimes  they  are   con- 


Fig.  148. — Corrugated  Sidewalk  Brick. 
structed  of  re-pressed  bricks,  which  give  closer  joints  and  more 
uniform  surface.  Thin  joints  are  desirable,  since  they  decrease 
the  tendency  for  weeds  and  grass  to  grow  in  them.  Sometimes 
sidewalk  bricks  are  made  with  a  corrugated  top  surface,  of  which 
Fig.  148,  shows  two  forms;  but  the  corrugations  are  of  no  advan- 
tage, and  it  is  hard  to  clean  the  snow  out  of  them.  Occasion- 
ally salt-glazed  brick  (§  734)  are  used  in  sidewalks;  but  this  is 
undesirable,  since  the  glazing  makes  the  bricks  slippery  and  also 
makes  it  more  difficult  to  detect  soft  bricks. 

925.  Direction  of  Rows.  There  is  considerable  difference  in 
practice  as  to  the  position  of  the  bricks  with  reference  to  the  side 
of  the  walk/  The  arrangement  shown  in  Fig.  149,  page  596,  is 
apparently  the  most  common,  and  may  be  called  the  longitudinal 
herring-bone.    The  arrangement  in  Fig.  150,  page  596,  is  superior 


596 


SIDEWALKS. 


[CHAP.   XIX. 


to  that  in  Fig.  149,  since  there  are  usually  no  bricks  in  the  triangu- 
lar corners  near  the  edge  of  the  walk,  and  weeds  and  grass  grow  in 
them,  thus  giving  the  walk  an  untidy  appearance.     Some  manu- 


Fig.  149.— Longitudinal  Herring-bone  Brick  Sidewalk. 

facturers  make  triangular  pieces  with  which  to  fill  these  corners, 
but  such  an  arrangement  will  cost  more  than  that  shown  in  Fig. 


5     '  I  I  i  I        '  I  |     '  I        '  I  '      1  I  I  I  I  I  II 


Fig.  150. — Diagonal  Herring-bone  Brick  Sidewalk. 

150.-    Fig.  150  is  easier  to  lay  than  Fig.  149,  since  it  is  less  difficult 
to  maintain  the  direction  of  the  courses.     Possibly  there  is  slightly 


,      1 

E 

Fig.  151. — Square-Course  Brick  Sidewalk. 


less  danger  of  stubbing  one's  toe  on  a  walk  laid  as  in  Fig.  149  than 
on  one  laid  as  in  Fig.  150.  Fig.  151  and  152  show  two  other  ar- 
rangements of  the  bricks;  but  neither  of  these  is  as  good  as  either 


BRICK    SIDEWALKS. 


597 


Fig.  149  or  Fig.  150,  on  account  of  the  continuous  joints  making 
the  displacement  of  the  bricks  more  likely  when  wheelbarrows, 
baggage  trucks,  or  other  wheeled  vehicles  are  run  over  the  walk. 
A  pleasing  variety  is  sometimes  obtained  by  introducing  different 
colored  bricks,  as  for  example  dark-colored  and  buff  bricks. 

The  side  of  the  walk  is  usually  protected  by  setting  a  row  of 


1 

_J_ 

1 

1 

,1 

1 

T 

€E 

.      j 

\ 

1 

1 

i 

1 

Fig.  152.— Block-in-Course  Brick  Sidewalk. 

bricks  on  edge,  as  shown  in  Fig.  149-52.  Sometimes  the  bricks 
are  set  on  end  to  form  a  curb,  and  some  manufacturers  make  a  brick 
block  or  tile  8X8X2  inches  to  be  used  as  curbs  for  sidewalks. 

926.  Laying  the  Bricks.  On  each  side  of  the  gravel  or  cinder 
foundation  should  be  placed  a  line  of  scantlings  approximately 
2X4  inches,  whose  top  edges  should  accurately  conform  to  the 
top  of  the  curbs  of  the  finished  walk.  Between  the  scantlings  is 
then  placed  a  2-inch  layer  of  fine  clean  dry  sand  upon  which  to  bed 
the  brick.  This  sand  should  be  spread  fairly  uniformly  with  shovels,, 
and  then  its  top  surface  should  be  made  smooth  and  uniform  and 
exactly  parallel  to  the  surface  of  the  finished  walk,  by  drawing  over 
it  a  template  whose  ends  run  on  the  scantlings.  For  several  pre- 
cautions applicable  in  this  work,  see  §  763  and  the  first  and  last 
paragraph  of  §  764. 

After  the  sand  bed  has  been  properly  prepared,  the  bricks  arc 
to  be  laid  by  men  standing  upon  the  brick  already  in  position  with- 
out disturbing  the  sand  cushion.  Care  should  be  taken  to  pre- 
serve the  direction  of  the  courses  and  also  to  secure  joints  of  uni- 
form width,  so  that  there  may  be  neither  a  needlessly  wide  joint  in 
closing  nor  any  cutting  of  the  brick.  The  bricks  should  be  laid 
with  as  close  joints  as  possible,  for  appearance  and  to  prevent  as 
far  as  possible  grass  and  weeds  from  growing  in  the  joints- 


598  SIDEWALKS.  [CHAP.    XIX. 

The  surface  of  the  walk  should  be  carefully  and  thoroughly 
rammed  to  settle  all  the  bricks  firmly  and  uniformly  into  the  sand 
cushion.  The  ramming  may  be  done  with  either  of  the  rammers 
shown  in  Fig.  138  and  Fig.  141,  page  527  and  543,  respectively. 
The  rammer  should  be  used  upon  a  hard  wood  plank  2  inches 
thick,  1  foot  wide,  and  6  or  8  feet  long.  Any  unevenness  of  the 
surface  after  the  walk  has  been  rammed  should  be  corrected  by 
taking  up  and  re-laying  the  defective  area.  After  the  walk  has 
been  rammed,  the  joints  are  filled  with  fine  dry  sand,  and  a  layer 
about  J-inch  thick  is  left  upon  the  surface  to  be  further  worked 
into  the  joints  by  traffic. 

927.  If  the  earth  comes  directly  against  the  edge  or  curb  of  the 
sidewalk,  it  will  stick  to  the  bricks  when  wet,  and  in  drying  will 
contract  and  pull  the  bricks  away  from  each  other.  The  cracks 
thus  formed  will  fill  with  dirt,  and  the  process  will  be  repeated  the 
next  dry  spell,  and  thus  the  joints  will  be  gradually  widened.. 
This  action  is  entirely  prevented  by  placing  3  or  4  inches  of  sand 
between  the  bricks  and  the  earth. 

Some  cities  use  a  concrete  curb  at  the  edge  of  the  brick  walk. 
This  curb  is  sometimes  2X8  inches,  and  sometimes  6X6  inches. 
The  cost  of  a  concrete  curb  is  hardly  justifiable,  since  the  chief 
advantage  of  it  is  obtained  by  the  use  of  sand  as  described  in 
the  preceding  paragraph. 

If  the  center  of  the  walk  is  above  the  surrounding  surface  and 
particularly  if  it  is  on  an  embankment,  there  should  be  considerable 
earth  against  the  sides  of  the  walk  to  prevent  the  expansion  of 
water  freezing  in  the  joints  from  crowding  the  curbs  out  and 
increasing  the  width  of  the  joints. 

928.  Transverse  Slope.  A  brick  sidewalk  should  be  laid  with 
a  slope  toward  the  street  of  }  or  £  an  inch  to  the  foot,  to  secure 
surface  drainage.  Not  infrequently  brick  sidewalks  bounded  by 
grass  plats  on  both  sides  are  laid  with  the  two  sides  on  the  same 
level,  and  the  center  is  raised  an  inch  or  more.  This  practice  is 
undesirable,  since  the  gutter  formed  at  each  side  of  the  walk  be- 
comes a  channel  to  carry  the  water  longitudinally  along  the  walk, 
whereas  the  water  should  be  permitted  to  flow  across  the  walk  into 
the  street  gutter.  Occasionally  the  crown  is  made  so  great  as  to 
confine  the  travel  to  the  center. 


BRICK   SIDEWALKS.  599 


929.  Brick  Crossings  on  Unpaved  Street.  These  are  usually 
laid  substantially  as  a  two-course  brick  pavement.  The  subgrade 
is  excavated  to  a  depth  of  14  to  16  inches,  according  to  the  char- 
acter of  the  soil  and  the  volume  of  the  traffic,  below  the  top  of  the 
finished  crossing.  The  foundation  should  be  excavated,  say,  6 
inches  wider  on  each  side  than  it  is  proposed  to  lay  the  bricks,  in 
order  that  there  may  be  a  shoulder  or  footing  to  support  the  outer 
brick;  and  the  edges  of  the  foundation  should  have  a  crown  of,  say, 
6  inches,  most  of  which  should  be  at  the  edge  so  that  the  finished 
crossing  may  have  a  slope  at  the  sides  that  will  be  easy  for  vehicle 
wheels  to  mount.  After  the  soil  has  been  tamped  to  consolidate 
it  and  to  reveal  any  soft  place,  a  layer  of  gravel  or  cinders  6  to  8 
inches  thick  is  then  laid  and  tamped.  Upon  this  foundation  is 
placed  a  layer  of  hard-burned  building  bricks  laid  flatwise.  The 
joints  of  the  lower  course  of  bricks  is  swept  full  of  fine  sand,  and  a 
cushion  coat  of  2  inches  of  sand  is  left  upon  the  brick.  The  top 
surface  of  the  sand  cushion  should  be  brought  parallel  to  the  finished 
surface  of  the  proposed  crossing,  by  the  use  of  a  lute  or  hand 
scraper.  The  sand  cushion  is  then  covered  with  very  hard-burned 
building  brick  or  with  rejected  paving  bricks  or  blocks,  set  on  edge 
and  properly  breaking  joints.  These  bricks  are  then  thoroughly 
rammed,  and  the  joints  are  swept  full  of  fine  sand. 

930.  Crossings  on  Brick  Pavement.  On  unpaved  streets  cross- 
ings are  laid  to  keep  pedestrians  out  of  the  mud,  and  on  rough  stone- 
block  pavements  crossings  are  constructed  to  provide  a  smooth 
surface  which  is  more  pleasant  to  walk  upon  and  also  more  easily 
cleaned  than  the  carriage-way  pavement;  but  on  streets  paved 
with  a  smooth  hard  surface  which  is  easily  cleaned,  as  brick,  special 
foot-way  crossings  are  not  necessary,  except  to  aid  pedestrians  in 
crossing  the  water  in  the  gutters.  To  confine  the  water  in  the 
gutter,  it  is  customary  to  raise  the  pavement  in  the  line  of  the 
crossing  so  that  the  surface  is  level,  or  nearly  so,  from  the  crown  of 
the  carriage-way  pavement  to  the  curb,  leaving  a  channel  next  to 
the  curb  which  is  either  left  open  or  bridged  with  a  cast-iron  plate. 
Fig.  153,  pa%ge  600,  shows  the  details  of  an  elevated  brick  crossing. 
Notice  that  Fig.  153  has  a  limestone  curb  and  a  brick  gutter. 
Fig.  154  and  155,  page  600,  show  the  gutter  at  the  end  of  an  elevated 
brick  crossing  when  a  concrete  curb  and  gutter  is  employed.     The 


600 


SIDEWALKS. 


[CHAP.   XIX. 


chief  difference  between  Fig.  154  and  155  is  in  the  form  of  the  false 
curb  or  head  stone  on  the  side  of  the  gutter  toward  the  center  of 
the  -street.  The  difference  in  the  merits  of  the  two  methods  is 
mainly  in  the  cost,  Fig.  154  usually  being  slightly  the  cheaper. 


PLAN 


I    I    I    i    I    i    i    i 


I     I     I     I     I     1     I     I     I     I3CT 


SECTION    A-B 


SECTION  C-D 

(otthe  centre) 

Fig.  153. — Elbvated  Brick  Crossing. 


SECTION  E-F 


In  both  cases  there  is  a  drop  of  1  inch  in  the  width  of  the  cast-iron 
bridge  plate.  Of  course,  the  crossing  could  be  carried  level  from 
gutter  to  gutter,  or  more  drop  could  be  put  into  the  gutter  plate. 

...       21  ii>  '£"  C I  Gutter  Rote 


t5>JfC.I  Gutter  Plate 

n 


Fig.  154. — Gutter  for  Elevated  Brick 
Crossing  with  Limestone  False  Curb. 


Fig.  155. — Gutter  for  Elevated  Brick 
Crossing  with  Concrete  False  Curb. 


As  far  as  the  use  of  the  carriage-way  pavement  is  concerned, 
an  elevated  crossing  is  undesirable,  particularly  where  the  pave- 
ment is  used  by  a  large  number  of  vehicles  or  where  there  is  con- 


BRICK    SIDEWALKS.  601 


siderable  rapid  traffic;  but  elevated  crossings  are  a  necessity  where 
a  considerable  volume  of  water  is  brought  to  a  corner  catch-basin 
or  where  the  street  is  nearly  level  longitudinally.  Some  of  the 
disadvantages  of  an  elevated  crossing  are  eliminated  by  placing  a 
catch-basin  at  each  side  of  the  corner  instead  of  one  at  the  corner 
—see  §  507. 

It  has  been  proposed  to  cast  the  street  names  on  the  bridge 
plates  used  at  elevated  crossings.  This  can  be  done  at  a  compara- 
tively small  cost,  and  would  put  the  street  name  in  a  convenient 
place  for  pedestrians;  but  unfortunately  these  plates  frequently 
get  broken,  and  further  the  name  on  the  crossing  plate  would 
not  be  visible  from  vehicles  and  street  cars. 

931.  Cost.  The  price  of  bricks  suitable  for  sidewalks  is  usually 
from  $7.00  to  $9.00  per  thousand.  Table  51,  page  518,  shows  the 
number  of  bricks  required  to  lay  a  square  yard.  The  cost  of  the 
earthwork  will  vary  with  the  character  of  the  soil  and  the  depth 
of  the  excavation.  The  cost  of  labor  in  placing  the  sand  cushion 
and  laying  the  brick,  varies  from  4  to  4 J  cents  per  square  yard. 

The  following  is  the  actual  cost  of  half  a  mile  of  6-foot  brick 
walk  laid  by  contract  in  a  city  in  Central  Illinois : 

Items.  Cost  per 

.  Sq.  \t>. 

Excavation  at  15  cents  per  cubic  yard $0 .  063 

Sand  and  gravel  12  inches  thick  at  $1.00  per  cubic  yard 333 

Brick  at  $7.00  per  thousand,  delivered 259 

Labor  at  $1.50  for  10  hours 043 

Total  cost  to  contractor  exclusive  of  tools  and  profits SO  698 

The  following  is  the  cost  of  constructing  a  brick  pavement  859 
feet  long  and  6  feet  2  inches  wide  by  the  city's  force  in  a  city  in 
Central  Illinois: 

Items.  Cost  per 

OQ.     ID. 

Brick  at  $8.00  per  thousand,  delivered $0 .  352 

Cinders  at  25  cents  per  cubic  vard,  at  furnace 042 

hauling  same,  1  day  at  $3.00. ,        .005 

Sand  at  80  cents  per  cubic  yard,  delivered 041 

Labor:  excavating — men,      10    days  at  $1.50/  Ooq 

team,      1|     "     ."     3.00^ U^ 

preparing  subgrade,    8       "      "     1 .  50 020 

grading  cinders,  6       u      "     1 .  50 015 

setting  forms,  2       "      "     1.50 005 

laying  brick,  16       "      "     1.50 041 

setting  curbs,  6       *      *     1 .50 010 

filling  joints,  etc.,        6£     "      "     1.50 .017 

Total  cost  exclusive  of  tools  and  superintendence. ,» $0,581 


602  SIDEWALKS.  [CHAP.   XIX. 

932.  Merits  and  Defects.  Brick  sidewalks  are  cheap,  fairly 
smooth,  and  not  slippery;  and  if  made  of  hard  brick  are  dry  in 
damp  weather  and  durable  under  very  heavy  travel.  Their 
defects  are :  (1)  they  are  rough  in  comparison  with  asphalt,  cement, 
and  the  best  stone  slabs;  (2)  they  are  untidy,  since  grass  and  weeds 
are  likely  to  grow  in  the  joints. 

933.  Cement  Sidewalks.  This  is  the  term  usually  applied 
to  an  artificial-stone  walk  composed  of  a  hydraulic-cement  con- 
crete base  and  a  cement-mortar  top.  Such  a  construction  is 
sometimes  called  a  concrete  walk,  and  sometimes  a  granolithic  walk. 
Numerous  patents  have  from  time  to  time  been  issued  for  various 
details  of  cement  walk  construction,  but  the  essential  features  are 
not  covered  by  patents.  Within  the  past  few  years  cement  walks 
have  become  very  common,  not  only  in  the  cities  of  the  Mississippi 
Valley,  where  natural  stone  suitable  for  walks  is  quite  expensive, 
but  also  in  the  eastern  cities,  where  suitable  natural  stone  is  plenty 
and  cheap.  Cement  walks  are  smooth,  pleasing  in  appearance, 
reasonably  cheap,  and  when  well  constructed  are  very  durable. 

934.  Foundation.  The  foundation  for  a  cement  walk  should  be 
practically  the  same  as  that  for  a  brick  walk  (see  §  922).  Since  the 
cement  walk  is  composed  of  large  rigid  blocks,  it  apparently  does 
not  require  so  heavy  a  foundation  as  a  brick  walk ;  but,  on  the  other 
hand,  a  slight  settlement  of  the  foundation  is  more  serious  with 
a  cement  walk  than  with  a  brick  one,  which  fact  seems  to  show 
that  the  cement  walk  should  have  a  heavier  foundation  than  a 
brick  one.  Water  freezing  under  a  cement  walk  is  liable  to  crack 
and  displace  the  blocks ;  and  therefore  if  the  soil  is  retentive  or  is 
not  already  artificially  underdrained,  it  is  wise  to  lay  a  line  of  tile 
longitudinally  under  the  proposed  walk,  which  shall  have  a  suffi- 
cient outlet  to  carry  the  subsurface  water  entirely  away.  It  is 
not  uncommon  to  excavate  the  foundation  1^  or  2  feet  below  the 
surface  of  the  proposed  walk,  apparently  that  the  porous  founda- 
tion may  act  as  a  drain  or  a  reservoir  to  prevent  water  from  stand- 
ing against  the  lower  side  of  the  concrete  and  perhaps  freezing  and 
lifting  the  walk;  but  a  tile  subdrain  is  cheaper  and  more  effective 
than  a  deep  but  undrained  foundation.  If  the  underdrainage  i ; 
even  fairly  good,  a  depth  of  6  inches  of  cinders  or  clean  gravel  will 
make  a  satisfactory  foundation,  provided  it  is  firmly  and  uniformly 


CEMENT   SIDEWALKS.  (50 '6 


tamped;  and  with  poor  drainage  the  thickness  need  not  be  more 
than  8  inches.  On  residence  streets  in  small  cities,  4  inches  of 
cinders  or  gravel  with  fair  drainage  would  doubtless  be  sufficient, 
although  the  foundations  are  usually  made  much  thicker. 

The  finished  surface  of  the  subgrade  should  be  made  exactly 
parallel  to  the  top  of  the  proposed  walk.  To  secure  this  condition, 
some  engineers  specify  that  the  depth  of  the  subgrade  is  to  be 
gaged  by  a  template  run  on  the  top  of  the  forms  after  they  have 
been  placed. 

935.  The  Forms.  The  edge  of  the  walk  is  marked  by  a  2-inch 
by  4-inch  scantling  securely  staked  in  position  with  its  top  face 
in  the  plane  of  the  top  of  the  finished  walk.  These  scantlings 
should  be  blocked  up  so  as  accurately  to  maintain  the  longitudinal 
grade  of  the  walk,  and  should  also  be  so  securely  staked  that  they 
will  not  be  crowded  out  by  the  tamping  of  the  concrete. 

The  forms  for  short  curves  should  be  made  by  sawing  the  proper 
curve  out  of  an  inch  plank,  and  then  nailing  enough  of  them  to- 
gether to  give  the  proper  thickness.  Care  should  be  taken  in 
joining  the  straight  form  to  these  curves,  to  prevent  an  unsightly 
change  of  direction.  Large  curves  can  be  made  by  using  a  ^-inch 
by  4-inch  plank  on  edge  for  the  side,  and  springing  it  into  the 
proper  curve  and  staking  it  fast;  but  care  must  be  taken  with  the 
ends  of  adjacent  pieces  to  secure  a  uniform  curve. 

936.  Concrete  Base.  In  residence  districts  of  small  cities,  the 
base  is  usually  3  inches  thick;  but  on  residence  streets  of  large 
cities  it  is  often  4  inches,  and  on  business  streets  it  is  sometimes 
5  inches.  The  base  consists  either  of  a  rich  natural-cement  con- 
crete or  of  a  rather  lean  Portland-cement  concrete.  The  latter  is 
the  more  common,  and  the  relative  merits  of  the  two  classes  of 
cements  for  this  purpose  will  be  considered  presently  (see  §  945). 
For  a  discussion  of  the  theory  of  proportioning  the  concrete,  see 
§  549 ;  and  for  the  method  of  mixing,  see  §  557. 

Any  moderately  hard  stone  is  suitable  for  making  the  concrete 
base ;  and  the  stone  is  usually  crushed  to  pass  a  1-inch  ring.  For  a 
discussion  of  the  relative  merits  of  gravel  and  broken  stone  for 
use  in  concrete,  see  §  553.  It  is  important  that  the  sand  or  gravel 
used  in  the  concrete  base  be  clean,  so  that  in  tamping  a  film  of  clay 
may  not  work  to  the  top  and  make  a  surface  of  separation  between 


604  SIDEWALKS.  [CHAP.  XIX- 

the  concrete  base  and  the  mortar  top.  The  following  proportions 
are  common :  1  part  Portland  cement,  3  parts  sand,  and  6  parts  of 
unscreened  broken  stone  (see  §  555). 

The  concrete  should  be  mixed  rather  dry  in  order  that  there  may 
not  be  a  film  of  water  on  the  top  of  the  concrete  base  which  will  pre- 
vent a  firm  union  between  the  top  and  the  base.  If  the  concrete 
is  too  moist,  the  mass  will  shake  like  wet  clay;  if  it  be  too  dry,  it  will 
rise  up  around  the  rammer  like  sand.  In  either  case,  the  mass  can 
not  be  suitably  compacted  by  ramming,  and  will  therefore  be 
comparatively  weak  and  porous  after  setting.  The  concrete 
should  be  thoroughly  and  uniformly  tamped  until  moisture  flushes 
to  the  surface.  Particular  care  should  be  taken  that  the  concrete 
base  is  well  consolidated  along  the  outer  edges,  so  that  frost  will 
not  break  them  up.  This  point  is  often  neglected,  because  tamp- 
ing the  edges  is  likely  to  crowd  the  forms  out  of  place. 

It  is  important  that  the  upper  surface  of  the  concrete  base 
should  be  exactly  parallel  to  the  top  of  the  finished  walk.  To 
determine  whether  this  condition  is  fulfilled  draw  a  properly-made 
template  over  the  tops  of  the  side  forms. 

937.  The  concrete  is  cut  into  blocks  by  laying  a  straight  edge 
on  the  marks  previously  made  on  the  side  forms  (§  942),  and  resting 
a  short  but  broad  blade,  see  Fig.  156,  against  the  straight  edge  and 
driving  it  downward  by  striking  it  with  an  iron  concrete-tamper. 
After  the  blade  has  been  driven  to  the  bottom  of  the  concrete,  it  is 
drawn  out  and  moved  along,  and  the  process  is  repeated  until  the 
concrete  is  cut  through  across  the  entire  width.  Some  engineers 
specify  that  the  space  made  by  the  cutting  tool  shall  be  immediately 
filled  with  fine  sand;  but  it  is  better  to  leave  it  entirely  open  (see 
§  942). 

938.  Wearing  Coat.  This  must  be  made  of  Portland  cement, 
since  natural  cement  is  not  sufficiently  strong  to  resist  the  abrasion 
of  traffic  and  the  effect  of  freezing  and  thawing.  The  wearing  coat 
is  usually  composed  of  one  part  of  Portland  cement  and  one  or  two 
parts  of  clean,  sharp,  coarse  sand  or  the  same  amount  of  granite 
or  quartz  screenings  that  will  pass  a  sieve  having  |-inch  meshes. 
The  proper  proportion  of  sand  to  cement  depends  upon  the  voids 
in  the  sand.  There  should  be  enough,  and  only  enough,  cement 
to  fill  the  voids.     If  there  is  not  enough  cement  to  fill  the  voids, 


CEMENT    SIDEWALKS. 


605 


the  sand  will  not  be  held  with  the  maximum  strength ;  and  if  there 
is  an  excess  of  cement,  the  walk  is  liable  to  crumble  under  travel, 
since  neat  cement  will  not  resist  abrasion  as  well  as  sand  and  cement. 
Sand  is  not  as  good  as  screenings,  but  is  cheaper  and  is  much  more 
commonly  employed. 

Sand  frequently  contains  a  considerable  proportion  of  soft  and 
easily  decomposed  constituents  which  renders  it  unfit  for  use  in  the 


r«-i 


Fig.  156. — Blade  for  Cutting  the  Concrete  Base. 

wearing  coat  of  cement  sidewalks,  since  the  friable  grains  soon 
pulverize  and  blow  away,  leaving  a  hole  or  pit  in  the  surface, 
which  not  only  looks  badly  but  also  tends  to  hasten  the  destruction 
of  the  walk.  Granite  screenings  are  frequently  used  instead  of 
natural  sand,  but  some  granites  contain  mica,  hornblende,  and 
feldspar  which  render  them  undesirable  for  use  in  cement  walks. 
Crushed  quartz  is  best  for  this  purpose,  but  is  expensive  on  account 
of  the  difficulty  of  crushing  it.  Pure  silica  sand  is  entirely  satis- 
factory. Screenings  are  considerably  more  expensive  than  sand 
{see  §  955),  and  if  used,  should  be  perfectly  free  from  fine  dust. 

The  thickness  of  the  wearing  coat  depends  upon  the  amount  of 
traffic,  a  thickness  of  \  an  inch  being  employed  where  the  traffic 
is  light,  and  1  inch  where  it  is  heavy.  The  mortar  for  the  wearing 
coat  should  be  mixed  rather  dry,  and  should  be  applied  before  the 
cement  in  the  concrete  base  has  begun  to  set,  in  order  that  the  two 
layers  may  firmly  unite.  The  mortar  is  to  be  brought  to  a  uniform 
thickness  by  laying  a  straight  edge  on  the  side  forms  and  drawing 


606  SIDEWALKS.  [CHAP.  XIX. 

it  longitudinally  along  the  walk.  The  mortar  should  then  be 
rubbed  and  compressed  with  a  float  (a  plasterer's  wooden  spreading 
trowel)  to  expel  the  air  bubbles  and  the  surplus  water.  Just  as  the 
cement  in  the  top  coat  begins  to  set,  it  is  to  be  rubbed  smooth  and 
hard  with  a  plastering  trowel,  sufficient  pressure  being  employed 
to  force  the  top  and  bottom  layers  into  close  contact  so  that  they 
may  firmly  adhere. 

Sometimes  the  mortar  is  inadvertently  made  too  wet,  and  an 
excessive  amount  of  water  appears  in  floating  and  troweling,  par- 
ticularly on  a  cool  damp  day.  To  take  up  this  water,  dry  cement 
is  sometimes  sprinkled  over  the  surface;  but  this  practice  is  very 
undesirable,  since  it  leaves  the  surface  too  rich  in  cement  and  likely 
to  be  spotted  in  color.  A  surplus  of  cement  makes  the  surface  of 
the  walk  more  friable  than  though  the  proper  proportion  of  sand 
had  been  used.  The  best  method  of  removing  this  excess  of  water 
is  to  absorb  it  with  a  dry  mixture  of  cement  and  sand  of  the  pro- 
portions used  for  the  top  coat,  and  then  there  will  be  no  excess  of 
cement  and  no  spottedness. 

In  troweling,  particular  care  must  be  taken  to  consolidate  the 
edges  of  the  blocks;  and  the  general  tendency  to  trowel  the  blocks 
low  in  the  center  must  be  carefully  guarded  against,  as  these  de- 
pressions retain  water  after  a  rain  and  keep  the  walk  needlessly  wet. 
The  troweling  should  be  done  so  that  when  a  4-foot  straight  edge  is 
laid  in  any  direction  upon  the  walk  a  space  greater  than  $  of  an  inch 
will  never  be  found  under  it,  and  seldom  a  space  greater  than  TV 
of  an  inch  will  be  found. 

Troweling  for  an  excessively  long  time  is  very  objectionable, 
since  it  is  liable  to  work  an  excess  of  cement  to  the  surface,  a  result 
which  makes  the  walk  more  slippery  and  less  durable. 

939.  While  completing  the  troweling,  the  wearing  coat  is  to  be 
separated  into  blocks  by  laying  a  straight  edge  to  the  marks  pre- 
viously made  upon  the  side  forms,  and  with  the  point  of  the  trowel 
cutting  through  the  wearing  coat  exactly  over  the  cut  previously 
made  in  the  concrete  base.  The  joint  is  then  finished  by  rubbing 
it  with  a  tool  similar  to  that  shown  in  Fig.  157.  The  edge  of  the 
walk  also  is  finished  by  running  over  it  a  tool  similar  to  that  shown 
in  Fig.  158,  the  front  face  of  the  tool  as  shown  being  placed  next 
to  the  wood  frame. 


CEMENT   SIDEWALKS.  607 


940.  Some  engineers  specify  that  after  the  troweling  has  been 
finished  and  the  joints  and  edges  have  been  rubbed  down,  the  entire 
surface  shall  be  brushed  with  a  damp  bristle-brush,  to  remove 
the  trowel  marks.  The  brush-finish  gives  a  uniform  dull  surface 
that  appears  better  than  the  surface  left  by  the  trowel.     See  §  527. 

Other  engineers  require  that  the  surface  shall  be  marked  with  a 


Fig.  157. — Cement-walk  Jointer. 


toothed  roller  somewhat  like   that  shown  in  Fig.  159,  page  608, 
the  object  being  to  render  the  walk  less  slippery  (see  §  952). 

941.  After  the  wearing  surface  is  finished,  the  walk  must  be 
protected  from  the  weather  and  other  injury  until  it  has  thoroughly 
set.    It  is  well  to  shield  the  walk  from  the  direct  rays  of  the  sun  and 


Fig.  158. — Cement- walk  Edge -former. 

from  strong  winds  for  at  least  one  day,  in  order  that  the  water 
required  for  the  setting  of  the  cement ,  may  not  be  lost  by  e vapori- 
zation. If  the  weather  is  dry,  it  is  well  to  keep  the  walk  moist  by 
sprinkling  it  frequently;  but  it  should  not  be  sprinkled  until  the 
surface  has  hardened,  lest  it  be  pitted  by  the  drops  of  water.  In  a 
very  dry  time,  the  necessity  for  frequently  sprinkling  the  surface 
may  be  obviated  by  covering  the  walk  with  sand,  straw,  etc. 

The  forms  should  not  be  removed  until  the  cement  has  set  so 
hard  that  there  is  no  danger  of  injuring  the  edge  of  the  walk  in  re- 
moving them. 

942.  Joints.  The  walks  should  be  formed  in  blocks  from  3  to 
8  feet  square,  to  prevent  settlement  of  the  foundation  or  contraction 
by  cold  from  making  unsightly  irregular  cracks.     If  the  walk  is  5 


608 


SIDEWALKS. 


[CHAP.    XIX. 


inches  thick,  the  blocks  may  safely  be  5  or  6  feet  square ;  and  if  the 
thickness  is  6  inches,  the  blocks  may  be  7  or  8  feet  square.  The 
concrete  base  is  usually  laid  in  a  continuous  mass,  and  then  cut  into 
blocks,  in  which  case  the  position  of  the  joints  should  be  deter- 
mined and  be  marked  upon  the  forms  before  the  concrete  is  laid. 
The  joints  should  be  continuous  across  the  entire  width  of  the 


Fro.  159. — Cement-walk  Imprint  Roller. 


walk,  i.  e.,  a  joint  should  not  come  opposite  the  middle  of  a  block, 
since  settlement  or  contraction  cracks  are  likely  to  start  from  the 
end  of  the  joint  across  the  middle  of  the  adjacent  block. 

Some  constructors  to  secure  a  more  complete  separation  of  the 
blocks,  divide  the  area  to  be  occupied  by  the  walk  into  compart- 
ments by  inserting  transverse  partitions  between  the  side  forms, 
and  then  construct  the  walk  in  alternate  blocks.  The  only  advan- 
tage of  this  construction  is  that  it  insures  a  complete  separation 
between  adjoining  blocks;  but  the  method  described  above  has 
given  no  trouble  in  practice.  A  few  constructors  not  only  buiid 
the  walk  in  alternate  sections,  but  leave  a  steel  partition  about  T\ 


CEMENT    SIDEWALKS.  609 


of  an  inch  thick  between  adjacent  blocks  until  the  concrete  has 
partially  set.  The  object  of  the  partition  is  to  leave  an  open  joint 
to  give  room  for  the  expansion  of  the  walk;  but  the  joint  is  likely 
to  get  filled  with  dirt  and  sand,  which  will  largely,  if  not  wholly, 
neutralize  the  supposed  advantage  of  the  open  joint. 

943.  In  closing  work  at  night,  the  concrete  should  be  finished 
at  a  joint  with  a  square  straight  end.  If  the  concrete  is  finished 
with  a  ragged  oblique  edge,  it  is  impossible  to  get  a  good  union 
between  the  two  days'  work  and  expansion  by  heat  is  liable  to 
cause  one  piece  to  slide  upon  the  other  and  break  the  wearing 
course.  The  wearing  coat  also  should  be  finished  up  to  a  joint. 
Sometimes  an  attempt  is  made  to  weld  new  mortar  to  that  already 
set,  but  alternate  freezing  and  thawing  is  likely  to  open  a  crack  at 
the  weld;  and  hence  welding  should  never  be  permitted.  The 
work  may  be  stopped  at  night  most  conveniently  by  inserting  a 
board  between  the  side  forms,  and  finishing  the  walk  against  it. 
No  patching  of  a  defective  block  after  the  cement  has  begun  to 
set  should  be  allowed. 

944.  Expansion.  There  is  occasionally  a  little  trouble  from 
the  expansion  by  heat  of  long  stretches  of  cement  walk  constructed 
without  open  or  expansion  joints.  The  coefficient  of  expansion 
of  concrete  is  about  0.000,005,5  per  degree  Fahrenheit.*  The  ex- 
pansion of  different  walks  differs  according  to  the  length  of  the 
walk,  the  exposure  to  the  sunshine,  the  openness  of  the  joints 
when  first  constructed,  the  anchorage  at  the  ends  of  the  walk,  the 
circulation  of  air  under  the  walk,  the  depth  of  the  walk  in  the 
ground,  etc.  Damage  by  expansion  seems  not  always  to  occur 
in  the  hottest  weather,  but  no  satisfactory  reason  is  known  for 
this  anomaly. 

The  expansion  of  the  walk  sometimes  causes  two  adjacent 
blocks  to  buckle  up,  producing  more  or  less  crushing  and  spalling 
of  the  edges.  This  occurs  most  frequently  in  the  dip  between 
two  ascending  grades,  since  the  blocks  in  expanding  move  in  the 
direction  of  the  least  resistance,  and  consequently  gradually  work 
down  hiii.  The  buckling  of  the  walk  may  be  prevented  by  insert- 
ing an  occasional  tar  joint,  say,  J  an  inch  thick.  If  a  tar  expan- 
sion-joint is  used,  the  upper  half  inch  of  the  joint  should  be  filled 

*  Jour.  West.  Soc.  of  Eng'rs,  Vol.  6,  p.  559. 


610  SIDEWALKS.  [CHAP.   XIX. 


with  sand  to  prevent  the  tar  from  being  tracked  over  the  surface 
of  the  walk.  Damage  by  expansion  is  more  common  after  the  walk 
is  two  or  three  years  old  than  before,  owing  to  the  fact  that  when 
first  made  there  is  more  or  less  empty  space  in  the  joint  which  takes 
up  the  expansion;  but  this  space  gradually  becomes  filled  with  dirt, 
and  no  longer  absorbs  the  expansion.  The  damage  from  expan- 
sion is  not  very  serious.  For  example,  a  contractor  who  has  laid 
250,000  square  feet  of  cement  walk  in  the  past  ten  years  has  been 
nailed  upon  to  repair  only  five  breaks  due  to  expansion. 

945,  Natural  vs.  Portland  Cement.  Portland  cement  must 
be  used  for  the  top  coat  of  walks,  since  natural  cement  is  not  strong 
enough  to  endure  the  abrasion  of  traffic  and  the  effect  of  freezing 
and  thawing;  but  as  far  as  strength  is  concerned,  the  base  could 
be  made  of  either  natural  or  Portland  cement.  Many  skillful 
contractors  claim  that  it  is  impossible  certainly  to  make  a  Portland- 
cement  top  adhere  firmly  to  a  natural-cement  base,  and  claim 
further  that  the  same  kind  of  Portland  cement  should  be  used  in 
both  the  base  and  top  so  that  a  difference  in  the  rate  of  set  may 
not  make  a  surface  of  separation  between  the  top  and  base;  while 
on  the  other  hand,  other  contractors  seem  to  have  no  trouble  in 
using  a  natural  cement  in  the  base  and  a  Portland  in  the  wearing 
coat.  Doubtless  the  latter  succeed  only  by  unusual  care ;  and  there- 
fore it  is  safer  to  use  Portland  in  the  base,  particularly  as  the  failure 
of  the  wearing  coat  to  adhere  firmly  to  the  base  is  the  most  common 
defect  of  cement  walks,  whether  the  base  is  made  of  natural  or  of 
Portland  cement.  Owing  to  the  recent  marked  decrease  in  price 
of  Portland  cement  in  America,  the  difference  in  cost  between  a 
Portland  and  a  natural-cement  base  is  not  so  great  as  formerly. 

946.  Transverse  Slope.  A  cement  walk  when  built  along  the 
side  of  a  street  should  have  a  transverse  slope  of  at  least  £  of  an 
inch  per  foot,  and  preferably  -^  or  J  of  an  inch;  but  should  never 
have  more  than  f  of  an  inch  per  foot.  A  slope  of  \  an  inch  per  foot 
gives  an  unpleasing  appearance,  and,  when  the  walk  is  icy,  pedes- 
trians slide  toward  the  gutter,  particularly  on  a  windy  day. 

When  the  walk  is  laid  on  comparatively  level  ground  in  a 
public  park  or  on  private  grounds,  it  should  be  crowned  to  drain 
the  surface.  If  the  center  is  raised  \  to  \  of  an  inch  per  foot  of 
half  width,  the  surface  will   always  be  practically  dry,  provided 


CEMENT   SIDEWALKS.  611 


it  is  an  inch  or  more  above  the  adjoining  surface,  and  provided 
dead  grass  and  leaves  are  not  allowed  to  wash  against  the  standing 
grass  and  form  a  dam.  A  crown  of  J  inch  per  foot  of  half  width 
is  ordinarily  sufficient  to  drain  the  depressions  left  in  troweling. 

947.  Color  of  Walk.  Ordinarily  cement  walks  have  an  un- 
pleasant glare,  particularly  where  a  considerable  area  is  laid 
together,  as  around  public  buildings,  fountains,  etc.  This  glare  can 
be  mitigated  by  coloring  the  walk.  The  coloring  matter  must  not 
contain  acids,  and  must  have  no  effect  upon  the  alkalies  of  the 
cement.  Dry  mineral  colors  seem  to  be  the  only  ones  that  can  be 
used,  as  apparently  all  liquid  coloring  matter  destroys  the  cement. 
Usually  any  coloring  matter  lessens  the  strength  of  the  mortar,  and 
causes  the  surface  to  flake  off;  and  therefore  no  more  should  be  used 
than  is  absolutely  necessary,  especially  of  the  ochres  (§  948). 
Ultramarine  is  an  exception  to  this  rule,  since  a  small  quantity 
increases  the  strength  of  the  mortar,  and  30  to  40  per  cent  may  be 
used  without  materially  decreasing  the  strength. 

Germantown  lampblack  is  more  frequently  used  than  any  other 
coloring  matter,  and  gives  a  bluish  gray  or  stone  color  of  inten- 
sity varying  with  the  amount  used.  It  can  be  had  at  drug  stores 
in  1-pound  packages,  and  costs  about  12  to  15  cents  per  pound. 
Four  pounds  per  cubic  yard  of  sand  gives  a  fairly  satisfactory  result, 
although  twice  as  much  is  frequently  recommended.  Lampblack 
is  light  dry  stuff,  and  it  is  difficult  to  get  it  thoroughly  incorporated 
with  the  mortar.  Some  contractors  add  it  to  the  cement,  and  mix 
the  two  by  passing  them  through  a  sieve;  but  a  better  method  is 
to  mix  the  lampblack  with  the  dry  sand  by  turning  once  or  twice, 
and  then  to  sprinkle  the  mass  and  bank  it  up,  and  allow  it  to  stand 
at  least  over  night,  when  the  coloring  matter  will  be  uniformly 
distributed  throughout  the  mass.  The  lampblack  and  sand  can 
stand  any  length  of  time  before  being  mixed  with  the  cement.      v 

Some  contractors  color  only  the  surface  of  the  walk  instead  of 
the  entire  wearing  coat  as  above.  There  are  two  ways  of  doing 
this:  1.  The  coloring  matter  is  added  to  a  mixture  of  sand  and 
cement  of  the  same  proportions  as  that  used  for  the  wearing  coat. 
This  mixture  is  sprinkled  over  the  wearing  coat  after  it  is  in 
place  and  then  the  surface  is  floated  and  troweled.  This  treat- 
ment is  repeated  two  or  three  times  until  the  desired  shade  is 


612  SIDEWALKS.  [CHAP.   XIX. 

obtained.  When  this  method  is  employed,  the  wearing  coat  must 
be  mixed  a  little  wetter  than  otherwise,  so  that  the  dry  colored 
mortar  may  be  properly  wrorked  into  the  wearing  coat.  This 
method  of  coloring  the  surface  is  not  so  good  as  the  preceding, 
since  the  coloring  matter  is  likely  ultimately  to  wear  through  and 
leave  the  walk  spotted.  2.  Another  method  of  applying  the  coloring 
matter  is  to  sift  or  sprinkle  it  over  the  surface,  and  then  to  trowel 
it  in.  This  is  a  very  poor  method,  since  the  coloring  matter  is  easily 
blown  away,  and  the  walk  is  likely  to  be  spotted  or  to  wear  so,  and 
also  to  flake  off  in  places  where  there  is  an  excess  of  coloring  matter. 
948.  Almost  any  color  can  be  produced  by  the  use  of  the  right 
coloring  matter.  The  following  list  of  colors  and  coloring  matter 
is  frequently  quoted. 

Quantity 

Color  Desired.  Ingredient  Used.  per  Bbl.  of 

Cement. 

Black Peroxide  of  Manganese 48  pounds 

Blue Ultramarine  Blue 20        " 

Brown Brown  Ochre 24        " 

Gray Lampblack 2       " 

Green Ultramarine  Green 24        '* 

Red,  dull Oxide  of  Iron 24       " 

bright Pompeian  or  English  Red 24        " 

sandstone Purple  Iron  Oxide 24        " 

Violet Violet  Iron  Oxide 24       " 

Yellow Yellow  Ochre 24 

950.  Sometimes  a  very  white  walk  is  desired.  White  can  not 
be  produced  by  adding  a  coloring  matter.  Some  Portland  cements 
bleach  out  and  make  whiter  walks  than  others.  To  secure  a  white 
walk,  use  white  sand  or  powdered  white  marble  and  perfectly  clean 
water,  and  keep  the  surface  of  the  walk  free  from  dirt  or  dirty 
water.  A  very  white  surface  can  be  obtained  by  using  pure  white 
slaked  lime  and  white  sand,  but  the  walk  will  have  no  durability. 
Sprinkling  the  ordinary  cement  walk  frequently  and  allowing  the 
sun  to  shine  upon  it  for  a  few  days  after  it  is  completed,  seems  to 
bleach  it. 

951.  Street  Signs.  It  has  been  proposed  to  indicate  the  names 
of  the  streets  by  inserting  colored  letters  in  the  cement  walk  at 
the  corner  of  the  block.  This  may  be  done  by  placing  wooden  or 
metal  letters  of  a  thickness  equal  to  the  wearing  coat  in  the  proper 
position  and  laying  the  wearing  coat  around  them,  and  then  remov- 
ing the  letters  and  filling  the  space  with  colored  cement-mortar. 


CEMENT   SIDEWALKS.  613 

952.  Slipperiness.  Ordinarily  cement  walks  are  not  slippery, 
though  occasionally  one  is  seen  that  is  somewhat  slippery.  There 
is  considerable  difference  of  opinion  among  contractors  as  to  the 
cause  of  the  slipperiness,  some  claiming  that  it  is  due  to  too  much 
troweling,  others  to  too  rich  mortar,  and  still  others  to  one  or 
another  particular  brand  of  cement.  Apparently  a  slippery  walk 
occurs  only  when  the  wearing  coat  is  rich  in  a  very  finely  ground 
cement,  and  is  troweled  excessively  long.  The  long  continued 
troweling  seems  to  work  an  excess  of  very  fine  cement  to  the  surface 
of  the  walk.  If  the  sand  is  coarse  and  sharp,  such  a  walk  will 
cease  to  be  slippery  when  the  film  of  neat  cement  has  worn  away; 
but  if  the  sand  is  very  fine,  the  walk  may  always  be  slippery. 

1 '  If  a  cement  walk  is  so  hard  that  one  may  strike  fire  with  the 
shoe  heel,  it  is  nearly  certain  to  wear  slick."  Walks  made  with 
granite  screenings  are  usually  smoother  than  those  made  of  sand, 
since  the  angular  fragments  of  granite  are  not  so  easily  displaced 
as  the  rounded  sand  grains  and  consequently  the  surface  is  not 
roughened  by  the  depressions  left  by  the  dislodged  particles. 

953.  Precautions.  Since  cement  walks  are  very  common  and 
are  often  built  by  inexperienced  workmen  without  adequate  super- 
vision or  inspection,  a  summary  will  be  given  of  some  of  the  precau- 
tions to  be  observed  if  first  class  work  is  desired.  1.  Use  clean 
sand,  particularly  in  the  wearing  coat.  2.  Use  the  same  brand 
of  Portland  cement  in  base  and  top.  3.  Thoroughly  mix  the  sand 
and  cement  dry.  4.  Use  a  minimum  amount  of  water,  i.  e.,  only 
enough  to  make  the  mortar  the  consistency  of  moist  brown  sugar. 
5.  Mix  the  mortar  and  the  broken  stone  until  each  fragment  of 
stone  has  mortar  adhering  to  every  point  of  each  face.  6.  Con- 
solidate the  concrete,  particularly  at  the  edges,  by  thorough 
tamping.  7.  Avoid  long  blocks,  and  also  broken  joints.  8. 
Under  no  consideration,  attempt  to  place  the  top  coat  if  there  is 
a  film  of  dirty  water  on  the  top  of  the  concrete  base.  9.  Apply 
the  wearing  coat  as  soon  as  the  base  is  in  position.  10.  Tamp 
the  wearing  coat  or  use  heavy  pressure  in  troweling  it.  11.  Finish 
the  surface  of  each  block  to  a  plane,  and  be  very  careful  that  it  is 
not  low  in  the  center.  12.  Keep  the  walk  damp  for  several  days 
after  it  is  finished.  13.  The  thickness  of  the  concrete  base  and 
also  of  the  wearing  coat  should  conform  to  the  specification,  and 
each  should  have  the  specified  proportions  of  sand  and  cement. 


614 


SIDEWALKS. 


[CHAP.   XIX. 


954.  Cement  Walk  Across  Driveway.  Cement  walks  fre- 
quently cross  private  driveways,  and  often  the  driveways  them- 
selves are  paved  with  what  is  practically  a  cement  walk,  except 
that  the  construction  may  be  a  little  heavier.  The  surface  of 
the  driveway  should  be  roughened  to  give  a  good  foot-hold  for 
horses.  One  method  of  doing  this  is  to  form  V-shaped  grooves, 
about  1  inch  wide  and  \  inch   deep   and  4  inches  apart,  across 


Fig.  160. — Cement-walk  Groover. 

the  driveway.  These  grooves  may  be  made  with  a  tool  some- 
what like  that  shown  in  Fig.  157,  page  607,  but  can  be  most 
easily  made  by  the  use  of  the  tools  hown  in  Fig.  160.  When 
a  cement  sidewalk  is  carried  across  an  unpaved  driveway,  the 
foundation  and  also  the  walk  itself  should  be  made  heavier;  and 
in  addition  the  crossing  should  be  widened,  the  added  portion 
being  constructed  with  an  inclined  surface  to  assist  the  wheels  in 
mounting  and  to  prevent  them  from  crushing  the  edge  of  the  walk. 
In  the  South  Side  Parks  of  Chicago,  at  intersections  of  unpaved 
streets  and  alleys,  the  edge  of  the  walk  is  carried  dow^n  18  inches 


CEMENT   SIDEWALKS.  615 


from  the  surface  of  the  walk  to  form  a  curb.  This  curb  or  header 
is  6  inches  thick  and  is  faced  the  same  as  the  surface  of  the  walk, 
and  its  upper  corner  is  finished  with  a  radius  of  1^  inches. 

955.  Cost  of  Cement  Walks.  Materials.  One  barrel  of  Port- 
land cement  will  lay  about  35  square  feet  of  walk  having  a  3-inch 
concrete  base  composed  of  one  part  cement  and  two  parts  of  sand, 
about  half  of  the  cement  being  required  for  the  base  and  half  for  the 
top.  If  gravel  is  used  instead  of  sand  and  broken  stone,  the  above 
proportions  will  still  be  approximately  true.  One  yard  of  gravel 
will  lay  about  80  square  feet  of  concrete  base.  One  yard  of  sand 
will  make  250  square  feet  of  wearing  coat.  One  yard  of  cinders 
will  cover  about  72  square  feet  4  inches  thick  after  being  tamped. 

Gravel  and  sand  can  usually  be  had  at  $1.00  per  cubic  yard, 
delivered.  Cinders  cost  from  15  to  50  cents  per  cubic  yard  at  the 
furnace,  and  will  usually  cost  50  cents  per  cubic  yard  to  haul. 
Granite  chips  that  will  pass  a  1-inch  mesh  and  be  caught  on  a  J-inch 
mesh  will  usually  cost  about  $4.00  per  ton  or  about  $5.60  per  cubic 
yard  (=  2,800  lbs.).  Screenings  of  undecayed  granite  will  usually 
cost  $5.50  per  ton  or  about  $7.70  per  cubic  yard. 

956.  Labor.  The  amount  of  labor  required  to  lay  cement  walks 
varies  greatly  with  the  organization  of  the  gang,  and  also  with  the 
energy  and  skill  of  the  superintendent.  A  man  can  do  the  excava- 
tion for  250  to  300  square  feet  per  day,  assuming  that  the  excava- 
tion is  to  be  only  10  or  12  inches  deep,  and  assuming  that  the  earth 
is  simply  cast  to  the  side,  and  assuming  further  that  the  earth  is 
in  good  spading  condition.  Under  the  conditions  assumed  above 
and  with  wages  of  common  labor  at  $1.50  for  10  hours,  the  exca- 
vation will  cost  only  about  J  a  cent  per  square  foot ;  but  most 
contractors  estimate  that  under  average  conditions,  it  will  cost  1 
cent  per  square  foot.  Wheeling,  grading,  and  tamping  the  cinders 
will  cost  about  \  a  cent  per  square  foot.  One  finisher  and  five 
common  laborers  should  on  the  average  lay  800  square  feet  of  walk 
in  10  hours,  exclusive  of  the  preparation  of  the  foundation;  but 
apparently  some  contractors  with  6  men  put  in  1,200  square  feet 
in  9  hours,  while  others  lay  only  600.  A  well  organized  gang  should 
lay  100  square  feet  of  walk  per  man.  If  common  labor  receives 
$1.50  per  day,  a  form  setter  will  receive  $2.00,  and  a  finisher  $3.50 
or  $4.00. 


616  SIDEWALKS.  [CHAP.  XIX. 

957.  Total  Cost.  The  following  represents  the  average  expe- 
rience of  a  prominent  contractor  in  Central  Illinois,  for  a  walk  5 
feet  wide  having  a  concrete  base  3  inches  thick  composed  of  one 
part  cement  and  six  parts  of  gravel  and  having  a  wearing  coat 
1  inch  thick  composed  of  one  part  cement  and  two  parts  of  sand. 

Cost. 
Items.  Cts.  per 

Sq.  Fr. 

Portland  cement  at  $2  75  per  bbl 8.1 

Cinders, — 6  inches  at  75  cents  per  cu  yd 1.0 

Gravel  at  80  cents  per  cu  yd 1.0 

Labor, — excavating  foundation 1.0 

placing  cinders 0.5 

setting  forms 0.2 

mixing  and  placing  concrete  for  base 0.6 

mixing  and  placing  wearing  coat 0.2 

troweling  and  finishing 0.5 

Teaming, — hauling  forms  and  tools 0.2 

Tools  and  lumber,  6  per  cent 0.7 

Total  cost  exclusive  of  superintendence,  guarantee,  and  profits. .      14.0 

958,  CINDER  WALKS.  Cinders  are  sometimes  employed  for 
the  surface  of  foot- ways;  but  usually  they  are  more  expensive 
than  gravel,  and  are  always  much  less  satisfactory.  They  are  dusty 
during  dry  weather  and  muddy  during  wet  weather  and  when  the 
frost  is  going  out  of  the  ground.  The  cinders  track  into  buildings, 
where  theyr  are  very  destructive  of  floors  and  are  otherwise  annoy- 
ing. CindeTS  easily  grind  up  under  traffic,  and  blow  away;  and 
therefore  new  material  must  be  added  continually.  They  are  light 
and  easily  washed  away;  and  consequently  after  every  rain  storm 
more  or  less  repairs  are  necessary,  to  say  nothing  of  removing  the 
cinders  from  catch  basins. 

To  make  a  cinder  walk  the  foundation  should  be  excavated 
at  least  6  inches  deep,  and  more  if  the  soil  is  retentive.  Then  a 
layer  of  cinders  6  inches  deep  should  be  put  into  the  trench  using 
care  to  cover  deeply  the  large  clinkers.  The  best  cinders  for  walks 
are  those  made  at  a  power  plant,  since  they  are  more  free  from  ashes 
than  those  in  stoves  and  household  furnaces  (see  §  923).  The 
cinders  should  be  flooded  and  tamped,  to  pack  the  finer  particles 
about  the  coarser  ones.      The    surface  should  have  a  crown,  and 


GRAVEL   WALKS.  617 


there  should  be  a  small  gutter  at  the  edge  to  preserve  a  line 
between  the  walk  and  the  lawn 

959.  GRAVEL  WALKS.  Gravel  is  employed  for  walks  chiefly 
in  parks  because  its  natural  color  usually  harmonizes  well  with 
that  of  grass  and  the  foliage  of  trees  and  shrubs,  and  also  because 
a  gravel  walk  is  not  as  hard  and  stiff  in  appearance  as  one  of  asphalt 
or  cement.  When  there  is  a  large  amount  of  travel,  or  where  the 
gravel  walks  are  not  well  constructed  or  properly  maintained, 
it  may  be  desirable  to  construct  asphalt  or  cement  walks  to  prevent 
disfiguring  foot-paths  in  the  turf  at  the  edge  of  the  walk  and  to 
obviate  the  use  of  unsightly  wire  or  chain  fences. 

To  construct  a  gravel  walk  on  a  sandy  subsoil,  excavate  a 
trench  4  or  5  inches  below  the  lawn  surface,  and  make  the  subgrade 
parallel  to  the  surface  of  the  proposed  walk;  and  then  lay  3  or  4 
inches  of  crushed  stone  or  bonding  gravel,  no  piece  or  pebble  of 
which  is  more  than  1  inch  in  greatest  dimension.  If  gravel  is  used, 
it  should  not  have  too  much  clay  in  it,  or  the  clay  will  work  through 
the  surfacing  material  and  make  the  walk  muddy  and  sticky,  and 
the  gravel  should  not  contain  too  little  binding  material,  or  the 
walk,  particularly  at  the  crown,  will  be  loose  and  stony,  as  the 
larger  pebbles  of  the  foundation  will  work  to  the  surface  of  the  walk 
owing  to  the  binding  material's  being  washed  out.  If  the  subsoil 
is  clay,  excavate  the  trench,  say,  8  inches  deep,  and  lay  5  inches 
of  cinders  reasonably  free  from  ashes;  and  then  upon  this  lay  2\ 
inches  of  crushed  stone  or  binding  gravel.  In  either  case,  the 
crushed  stone  or  gravel  should  be  rolled  with  a  5-ton  steam  roller, 
substantially  as  for  a  gravel  road  (§  254),  or  for  a  broken-stone 
road  (§  341-45). 

The  top  of  the  foundation  should  be  made  exactly  parallel  with 
the  surface  of  the  finished  walk. 

The  wearing  surface  should  consist  of  from  \  to  \  inch  of  fine 
torpedo  gravel,  i  e..  sand  having  grains  from  i  to  J  inch  in  greatest 
dimension.  The  surface  of  the  walk  should  have  a  crown  of.  say, 
2  or  3  per  cent  of  its  width ;  but  if  the  crown  is  too  great,  the  torpedo 
sand  will  be  washed  into  the  gutter.  The  edges  of  the  gravel  sur- 
face should  be  depressed  about  \\  inches  below  the  adjoining 
lawn. 

Paved  gutters  are  very  undesirable,  but  where  the  walk  is  on 


61b  SIDEWALKS.  [CHAP.  XIX. 

a  steep  grade  they  are  a  necessity.  A  neat  and  durable  gutter 
may  be  formed  of  small  cobble  stones.  If  the  slope  of  the  adjoining 
ground  is  such  that  the  surface  water  is  likely  to  flow  onto  the  walk, 
a  sod  gutter  should  be  formed  on  the  upper  side  of  the  walk.  This 
is  done  by  sinking  the  turf  alongside  and  parallel  to  the  walk,  to 
form  a  broad  shallow  depression.  This  gutter  should  have  no 
low  places  which  will  catch  and  retain  silt.  These  sod  gutters 
should  have  frequent  inlets  into  an  underground  drain. 

960.  MACADAM  WALKS.  Crushed-stone  walks  are  constructed 
in  substantially  the  same  way  as  described  above  for  gravel  walks, 
except  that  the  surface  is  covered  with  stone  screenings  instead 
of  torpedo  sand.  The  fragments  should  not  be  more  than  £  inch 
in  greatest  dimension  if  the  stone  is  hard;  but  if  it  is  soft,  the  pieces 
may  vary  from  J  to  J  inch  in  diameter.  A  surface  of  crushed 
limestone  is  pleasant  to  walk  upon;  but  its  color  is  trying  on  the 
eyes,  and  does  not  harmonize  well  with  the  color  of  the  grass  and 
the  foliage  of  trees  and  shrubs.  Crushed  granite  makes  a  durable 
walk,  and  usually  has  a  satisfactory  color;  but  the  particles  are 
so  sharp  as  speedily  to  cut  out  thin-soled  shoes.  A  walk  surfaced 
with  crushed  stone  is  less  satisfactory  both  to  walk  upon  and  in 
appearance  than  one  having  a  surface  of  fine  gravel. 

961.  PLANK  WALKS.  In  the  past  plank  sidewalks  have  been 
very  common,  but  owing  to  the  increasing  cost  of  lumber  and  to 
the  introduction  of  bricks  for  walks,  they  are  much  less  common 
now  than  formerly.  There  is  great  variety  in  the  forms  of  con- 
struction employed;  but  as  a  rule  the  design  is  poor,  little  or 
no  attention  being  given  to  the  conditions  necessary  to  secure 
durability.  However,  the  standard  plank  sidewalk  adopted  by 
the  City  of  Omaha.  Neb.,  in  1899,  is  an  exception.  Fig.  161, 
page  619,  shows  three  views  of  the  standard  6-foot  walk.  The 
specifications  for  plank  walks  in  Omaha  are  as  follows :  * 

1 :  Plank  walks  shall  be  built  in  accordance  with  the  standard 
general  plans  hereto  attached  [Fig.  161],  to  the  exact  height  and 
line  given  by  the  engineer.  The  stringers  shall  not  be  less  than 
12  feet  Jong,  except  when  necessary  at  the  end  of  the  walk,  and 
shall  break  joints  and  be  placed  on  bricks  not  more  than  6  feet  apart, 


*  By  courtesy  of  Andrew  Bosewater,  City  Engineer. 


PLANK   WALKS. 


619 


resting  upon  a  solid  foundation.  The  stringers  shall  be  cut  square 
at  the  ends,*  and  shall  be  closely  fitted  at  the  joints;  and  each 
joint  shall  be  toe-nailed  with  two  nails  4  inches  long.  This  part 
of  the  work  shall  be  accepted  by  the  City  Engineer  before  the 
planking  is  laid. 

"All  lumber  shall  be  white  pine,  square  edged,  and  shall  grade 






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LONGITUDINAL   SECTION 


TRANSVERSE   SECTION 
Fig.  161. — Omaha  Plank  Sidewalk. 

as  No.  1.  The  planks  shall  have  a  width  of  not  less  than  8 
inches,  nor  more  than  12  inches,  a  uniform  thickness  of  not  less 
than  2  inches,  and  a  length  equal  to  the  full  width  of  the  walk. 
The  planks  must  be  laid  with  a  |-inch  air  space  between  them, 
and  there  shall  be  a  space  of  at  least  4  inches  between  them  and 


*  The  Cincinnati  specifications  require  the  stringers  to  be  joined  with  a  3-inch 
half-lap  splice  which  is  spiked. 


620  SIDEWALKS.  [CHAP.   XIX. 

the  ground.  The  planks  shall  be  nailed  at  each  intersection  with 
two  nails  for  8-inch  planks  and  with  three  nails  for  planks  more 
than  8  inches  wide.  The  nails  shall  be  4  inches  long,  and  shall  be 
either  cut  nails  weighing  twenty  to  the  pound  or  wire  nails  weigh- 
ing thirty  to  the  pound,  with  heads  TV  inch  in  diameter.  The 
nails  shall  be  drifen  in  the  center  of  the  stringer,  and  the  heads 
shall  be  driven  I  inch  below  the  surface  of  the  plank.  Any  lum- 
ber split  or  otherwise  injured  in  construction  shall  be  removed  and 
be  re-placed  with  good  material. 

1 1  At  each  edge  of  the  walk  shall  be  securely  fastened  a  No.  10 
galvanized  iron  wire,  with  a  wire  staple  in  each  end  of  each  plank." 

962.  Cost,  In  Omaha  in  1899,  plank  cost  $19  per  thousand 
feet  board  measure,  and  sills  $22;  labor  exclusive  of  excavating 
and  grading,  $11  to  $12  per  thousand  feet  of  lumber;  wire  and 
stapling  1J  to  2  cents  per  lineal  foot  of  walk.  A  6-foot  walk  com- 
plete cost  39  to  40  cents  per  lineal  foot. 

963.  STONE  SIDEWALKS.  One  of  the  earliest  methods  of  pav- 
ing foot-ways  was  to  cover  them  with  natural  stone  flagging,  and 
such  walks  are  still  very  common  where  flagstones  of  suitable  size 
may  be  readily  obtained.  If  hard  and  smooth  and  well  laid,  nat- 
ural stone  slabs  make  a  fairly  durable  and  satisfactory  walk.  A 
walk  made  of  split  flagstones  is  ordinarily  a  little  smoother  than 
one  made  of  brick,  but  is  not  so  smooth  as  a  cement  walk.  If  the 
stone  is  tool-dressed,  it  may  be  nearly  or  quite  as  smooth  as  a 
cement  walk. 

Granite,  limestone,  and  sandstone  are  often  used.  The  kind  of 
stone  to  be  employed  in  any  particular  locality  will  depend  upon 
the  availability  of  the  stone  and  the  service  required  of  it. 

On  business  streets  where  large  blocks  are  required  to  span  coal 
or  storage  vaults  under  the  sidewalk,  and  where  large  loads  are 
likely  to  be  transported  over  it  from  the  curb  to  the  building,  gran- 
ite is  generally  used;  but  it  is  expensive,  and  wears  slippery,  so  that 
when  laid  upon  a  crowded  business  street  its  surface  must  fre- 
quently be  roughened  to  prevent  its  becoming  dangerously  slip- 
pery. It  is  largely  used  in  the  eastern  cities  where  cheap  water- 
transportation  can  be  had.  Sandstone,  when  sufficiently  hard  to 
resist  abrasion  satisfactorily,  makes  the  best  flagstones,  since  its 
gritty  nature  prevents  it  from  wearing  slippery.     In  and  around 


STONE   WALKS.  621 


New  York  city,  Hudson  River  bluestone,  a  variety  of  sandstone 
(see  §  517),  is  much  used  for  this  purpose.  .  In  the  west,  Bedford 
(Ind.)  limestone  is  employed,  although  it  chips  and  spalls  too  easy 
for  the  best  results. 

On  residence  streets,  the  flagstones  are  laid  upon  the  natural 
soil  or  upon  a  foundation  of  cinders  or  gravel.  If  laid  directly 
upon  the  soil,  the  stones  are  likely  to  become  displaced  by  the  ac- 
tion of  frost ;  and  therefore  they  should  be  laid  upon  a  sand  cushion 
resting  on  a  well-rammed  bed  of  porous  gravel  or  cinders,  and 
should  be  carefully  bedded  so  as  to  preserve  a  uniform  surface. 

The  flagstones  should  be  as  large  as  is  consistent  with  economy, 
since  there  will  then  be  fewer  joints  and  less  likelihood  of  the  sur- 
face of  the  walk  becoming  uneven.  On  the  other  hand,  if  the  size 
be  made  too  great,  the  cost  will  be  excessive,  as  it  is  more  expensive 
to  quarry  and  to  transport  large  blocks  than  small  ones,  and  there 
is  also  more  likelihood  of  breakage.  As  a  rule  the  stones  should 
not  contain  less  than  15  or  16  square  feet,  although  blocks  1J  by 
2 \  feet  are  not  uncommon.  The  thickness  of  the  flagstones  for 
walks  on  residence  streets  laid  upon  a  solid  foundation  usually 
varies  from  2  to  3  inches.  The  edges  should  be  cut  straight  and 
square,  and  smooth  enough  to  lay  thin  joints.  The  stones  should 
be  laid  with  their  length  across  the  walk  to  prevent  pedestrians 
from  walking  along  the  middle  of  a  row  of  stones  and  wearing 
them  hollow;  and  the  stones  should  break  joints,  so  as  to  prevent 
continuous  longitudinal  joints. 

964.  Crossing  Stones.  Foot-ways  of  flagstones  are  usually  pro- 
vided across  pavements  which  are  rough  to  walk  upon  or  are  likely 
to  be  muddy.  These  crossings  consist  of  stones  12  to  14  inches 
wide  laid  in  rows  across  the  street,  the  rows  being  6  or  8  inches 
apart,  and  the  stones  6  or  8  inches  thick,  and  3  to  6  feet  long. 

The  ends  of  the  stones  should  be  cut  on  a  bevel  so  that  there 
may  be  no  joints  in  the  direction  of  the  travel.  The  best  arrange- 
ment of  the  end  joints  is  shown  in  Fig.  162,  page  622.  Not  infre- 
quently the  joints  all  slope  toward  one  end  of  the  crossing,  in 
which  case  some  of  them  are  parallel  to  the  traffic  going  around 
the  corner,  and  hence  this  arrangement  is  not  so  good  as  the  one 
shown  in  Fig.  162.  It  is  usually  specified  that  the  ends  shall  be 
dressed  to  lay  |-inch  joints  for  the  full  thickness  of  the  stone,  and 


622 


SIDEWALKS. 


[CHAP.   XIX. 


that  the  upper  surface  shall  be  dressed  so  as  to  have  no  depressions 
of  more  than  I  inch.  The  stones  should  be  firmly  bedded  upon 
the  foundation. 


'{'<'<'<'/  7  '/  '/  '/ 


Fig.  162.— Stone  Cross-walks. 

965.  Cost.     The  catalogue  price,  per  square  foot,  of  Potsdam 
sandstone  sidewalk  flags  2  inches  thick,  f.  o  b.  cars  at  Potsdam, 
N.  Y.;  is  as  follows: 
2  feet  wide 9  cts  per  sq.  ft         6  feet  wide 25  cts.  per  sq.  ft. 


3     ' 

u 

...   12   " 

" 

tt 

!< 

7 

n 

a 

...  32    " 

•  a 

a 

ti 

4     " 

ti 

...   15   w 

>< 

:t 

8 

it 

<< 

...   40    " 

u 

u 

.-» 

5     •' 

it 

...   20    ': 

" 

it 

:( 

and  the  cost  price  per  lineal  foot  of  crossing  stones  at  the  same 
place  is  as  follows: 

10  inches  wide 12  cents        16  inches  wide 20  cents 

12       "  'f     15     "  18      "  "     24     l: 

14      «         "    17     "  24      "         "    30     "■ 


TAR    WALKS — COMPARISON    OF    WALKS.  G23 

In  New  York  city,  Hudson  River  bluestone  sidewalk  flags  cost 
from  16  to  22  cents  per  square  foot  delivered  on  the  street,  and 
the  cost  of  laying  is  about  2\  to  3  cents  per  square  foot.  In  Bos- 
ton, Hudson  River  bluestone  crossings  cost  29  to  30  cents  per 
square  foot  f.  o.  b.  the  wharf,  and  cost  about  2  cents  to  haul  to  the 
street. 

966.  TAR  WALKS.  Foot-way  pavements  made  of  concrete  in 
which  coal  tar  is  the  binding  material  have  been  widely  used,  par- 
ticularly in  England.  Some  tar  pavements  have  given  entirely 
satisfactory  results;  but  usually  they  have  been  very  unsatisfactory, 
wearing  rapidly  and  becoming  unpleasantly  soft  in  hot  weather. 
Tar  walks  have  practically  been  abandoned. 

Numerous  methods  were  tried,  differing  from  each  other  chiefly 
in  the  materials  mixed  with  the  tar.  Ashes,  sand  and  gravel, 
or  cinders  were  generally  preferred.  The  best  construction  con- 
sisted of  a  4-inch  foundation  of  dry  pebbles  thoroughly  coated  with 
tar  and  compacted  while  hot,  and  a  1-inch  wearing  coat  composed 
of  dry  screened  sand  saturated  with  tar  and  rolled  into  place  while 
hot.     This  pavement  usually  costs  5  to  6  cents  per  square  foot. 

967.  COMPARISON  OF  WALKS.  A  walk  should  be  smooth  but 
not  slippery,  should  dry  quickly  after  a  rain,  should  be  durable 
and  not  easy  to  get  out  of  repair,  and  should  be  low  in  first  cost. 
In  the  order  of  smoothness  the  principal  materials  rank  about  as 
follows:  asphalt  and  cement,  stone  slabs,  brick,  plank,  gravel  and 
macadam.  In  the  readiness  with  which  they  dry  after  a  rain  the 
materials  rank  about  as  follows:  asphalt  and  cement,  stone  slabs, 
bricks,  plank,  macadam,  gravel.  In  durability  they  rank  about 
as  follows:  brick,  cement,  stone,  gravel  and  macadam,  asphalt, 
plank.  The  cost  varies  so  much  with  the  locality  and  the  form  of 
construction  that  it  is  impossible  to  give  their  rank  except  in  a 
particular  case.  Cement  and  brick  seem  to  be  the  general  favor- 
ites, the  first  where  a  first  class  walk  is  desired  and  the  second 
where  a  cheap  walk  is  required.  The  roots  damage  brick  walks 
much  less  than  those  made  of  cement. 


CHAPTER  XX. 
BICYCLE   PATHS  AND   RACE   TRACKS. 

Art.  1.    Bicycle  Paths. 

969.  A  bicycle  in  the  eyes  of  the  law  is  a  vehicle  and  is  entitled 
to  travel  upon  the  public  highways  subject  to  similar  rights  of 
other  travelers;  and  the  bicycle  has  come  into  such  general  use  that 
a  reasonable  provision  for  this  class  of  traffic  should  receive  the 
careful  consideration  of  all  officials  charged  with  the  care  of  public 
highways.  It  is  frequently  claimed  that  the  bicycles  outnumber 
other  vehicles  six  to  one;  but  this  can  be  hardly  true  for  the  whole 
country,  although  it  may  be  true  in  the  cities.  It  is  certainly  true 
that  the  use  of  the  wheel  has  extended  to  every  profession  and  oc- 
cupation in  life,  and  that  the  bicycle  has  become  a  familiar  object 
in  every  civilized  land.  The  great  number  of  men  and  women  who 
use  the  bicycle  as  a  conveyance  both  for  business  and  for  pleasure 
are  rightly  entitled  to  be  placed  upon  an  equal  footing  with  pedes- 
trians who  use  the  sidewalks  and  with  those  who  ride  in  other 
vehicles  upon  the  carriage  ways. 

The  construction  of  cycle  roads  will  be  considered  under  two 
heads :  City  Bicycle  Ways,  and  Country  Bicycle  Paths. 

970.  CITY  BICYCLE  WAYS.  The  wheel  being  recognized  as  a 
proper  conveyance  and  as  entitled  to  the  use  of  the  street  under 
reasonable  restrictions,  the  question  arises  as  to  what  portion  of  the 
street  the  wheelman  shall  use  and  whether  any  special  construction 
is  required  for  their  accommodation. 

In  business  districts  and  in  residence  districts  having  fairly 
smooth  pavements,  it  seems  reasonable  to  confine  the  bicycle  traffic 
to  the  carriage  way;  but  on  residence  streets  where  the  pedestrian 
travel  is  light  and  the  carriage  way  is  not  surfaced  with  a  material 

624 


ART.   1.]  BICYCLE   PATHS.  625 

which  is  suitable  for  bicycle  travel,  the  wheelmen  should  be  per- 
mitted to  use  the  sidewalks  under  proper  rules  regulating  the  speed, 
particularly  in  meeting  and  passing  pedestrians.  However,  there 
are  main  avenues  of  travel  to  the  business  district  and  to  parks, 
ball  grounds,  summer  resorts,  etc.,  where  neither  the  carriage  ways 
nor  the  sidewalks  afford  reasonable  facilities  for  the  wheelman  and 
where  the  volume  of  bicycle  travel  for  both  business  and  pleasure 
is  sufficient  to  require  a  special  construction  for  its  proper  accommo- 
dation. Some  cities  lay  smooth  pavements  on  leading  thorough- 
fares for  the  accommodation  of  wheelmen,  while  others  construct 
special  cycle  ways  on  unpaved  streets,  and  sometimes  at  the  sides 
of  paved  streets  having  a  dense  vehicular  traffic.  In  some  cases 
special  cycle  ways  are  constructed  at  the  expense  of  the  city  and 
in  other  cases  by  private  contributions  of  wheelmen. 

Where  there  is  any  considerable  amount  of  bicycle  traffic,  it  is 
true  economy  to  set  apart  a  certain  portion  of  the  street  for  the  use 
of  the  wheelmen,  since  the  traffic  can  not,  with  safety  to  pedestrians, 
be  accommodated  upon  the  sidewalks,  and  since  it  is  much  cheaper 
to  construct  a  pavement  suitable  for  a  cycle  carrying  100  pounds 
on  a  rubber  tire  than  to  construct  a  pavement  for  a  truck  concen- 
trating perhaps  2,000  pounds  upon  a  steel-tire.  Further,  cycle 
ways  are  much  cheaper  to  construct  than  sidewalks,  often  cost- 
ing one  fourth  or  one  fifth  as  much. 

971.  Location.  Some  cities  have  allotted  a  strip  in  the  middle 
of  the  street  for  the  use  of  wheelmen,  but  the  result  has  not  been 
satisfactory  owing  to  the  difficulty  of  keeping  teamsters  from  tres- 
passing thereon.  The  cycle  way  should  be  either  on  the  edge  of  the 
roadway  next  to  the  curb,  or  in  the  parking  between  the  curb  and 
the  shade  trees,  the  former  probably  being  the  better  on  an  unpaved 
street  and  the  latter  on  a  paved  street  (see  §  468) . 

972.  Width.  The  width  should  depend  upon  the  amount  of 
cycle  traffic,  and  varies  from  3  to  16  feet,  but  is  seldom  less  than  4 
feet  for  city  paths.  One  wheel  can  pass  another  at  speed  on  a 
4-foot  path,  but  not  safely  upon  a  narrower  path. 

973.  Materials.  The  wearing-surface  may  consist  of  a  layer  of 
sand,  gravel,  cinders,  or  crushed-stone  screenings  on  an  earth  bed. 
or  it  may  consist  of  plank  laid  upon  timber  mud-sills,  or  it  may  be  a 
strip  of  sheet  asphalt  laid  upon  a  rough  stone-block  pavement.    A 


626  bicycle  paths  a:nd  race  tracks.        [chap.  XX. 

layer  of  screened  black  cinders  (§  922)  about  1  inch  thick  on  a  firm 
foundation  makes  a  fairly  good  cycle  path ;  and  a  layer  3  to  6  inches 
thick,  if  sprinkled  and  rolled  or  tamped,  makes  an  excellent  surface. 
The  chief  advantages  of  cinders  are  that  they  are  usually  cheap, 
are  always  dry,  and  give  a  fairly  firm  surface;  while  the  principal 
disadvantages  of  cinders  are  (1)  that  they  are  not  durable,  since  in 
dry  weather  they  powder  up  and  blow  away,  and  in  wet  weather 
they  wash  off,  and  (2)  that  the  sharp  angular  particles  are  destruc- 
tive of  bicycle  tires. 

A  mere  sprinkling  of  coarse  sand  on  a  bed  of  hard  and  well 
drained  earth  makes  a  fine  surface,  but  one  that  is  easily  damaged 
by  the  feet  of  horses  and  cattle  or  by  the  wheels  of  ordinary  vehicles. 
A  layer  of  cementing  gravel  J  to  1  inch  thick,  upon  a  well  drained 
and  thoroughly  consolidated  earth  bed  makes  a  durable  and  pleas- 
ing bicycle  road.  The  largest  pebbles  should  not  be  more  than  \  to 
f  of  an  inch  in  longest  dimension,  and  the  mass  should  contain 
sufficient  binding  material  (see  §  345)  to  keep  the  surface  firm  and 
hard.  If  the  gravel  contains  much  clay,  the  surface  will  be  sticky 
and  muddy  during  a  wet  time. 

The  best  cycle  ways  are  constructed  much  the  same  as  first- 
class  broken-stone  roads,  except  that  the  layers  need  not  be  as 
thick  and  do  not  require  as  much  rolling.  The  surface  should  be 
finished  with  a  layer  of  stone  screenings  i  to  J  inch  thick,  the  size 
ranging  from  \  inch  to  dust. 

In  localities  where  lumber  is  cheap,  it  is  common  to  construct 
cycle  ways  of  plank  very  much  as  sidewalks  are  made — see  §  976 
and  §  977. 

974.  Grade.  For  obvious  reasons,  the  grade  of  the  cycle  ways 
now  under  consideration  must  be  practically  the  same  as  that  of  the 
street  pavements  (see  §  471  and  §  479). 

975.  Cross  Section.  Since  the  cycle  way  is  usually  compara- 
tively narrow  it  is  immaterial  whether  its  surface  be  slightly  crown- 
ing or  have  a  small  fall  toward  only  one  side;  but  the  surface  of  the 
way  should  be  a  little  above  the  adjoining  ground  to  afford  good 
surface  drainage. 

976.  Examples.  Fig.  163,  page  627,  shows  five  plans  that  have 
been  used  in  constructing  city  cycle  ways.  Plans  A,  B,  and  C 
are  constructed  of  wood ;   and  D  and  E  are  constructed  of  gravel 


ART.   1.] 


BICYCLE   PATHS. 


62? 


or  broken  stone.     The  curb  on  the  right-hand  side  of  Plan  D  is 
supported  by  being  spiked  to  posts  firmly  set  into  the  ground. 


W 


'teT-^&t 


— /  \ 


SECTION  A 


SECTION   B  SECTION  C  SECTION  D  SECTION  E 

Fig.  163.— Plans  for  City  Bicycle  Paths. 

977.  Fig.  164,  page  628,  shows  the  four  standard  forms  of  cycle 
ways  employed  by  the  City  of  Portland,  Oregon.  The  following 
are  the  specifications:* 

"Plan  A  is  built  of  timber  and  consists  of  mud  sills,  4X6  inches,  placed 
at  right  angles  to  the  path,  4  feet  apart  center  to  center.  Where  the  side 
slope  of  the  street  surface  is  flat,  the  sills  will  be  laid  broad-side  down;  but 
where  the  side  slope  is  steep,  they  will  be  set  on  edge.  The  sills  must  be 
bedded  solidly  in  their  places,  and  must  be  level  and  at  such  an  elevation 
that  the  surface  water  from  the  street  can  pass  under  the  planks  to  the  gutter. 
Along  the  outer  edge  of  the  cycle  way  a  slight  ditch  must  be  excavated.  The 
covering  will  consist  of  five  planks,  2X12  inches,  sized  to  a  thickness,  in 
lengths  not  less  than  16  feet.  They  must  be  laid  close  together  and  break 
joints  not  less  than  4  feet.  Each  plank  must  be  nailed  to  each  mud  sill 
with  a  spike  in  each  edge  of  the  plank  at  the  intermediate  sills  and  three 
spikes  at  each  end,  the  spikes  being  6  inches  long.  The  plank  surface  will 
generally  be  placed  one  foot  from  the  curb,  and  on  the  same  grade  as  it.  All 
the  labor  of  building  the  cycle  way  must  be  done  in  a  good  and  workman- 
ship manner. 

u  Plan  B  is  built  without  timber  except  where  drain  boxes  are  necessary. 
The  center  of  the  shallow  ditch  on  the  roadway-side  of  the  cycle  way  will 
be  6  feet  from  the  curb.  The  material  from  this  ditch  will  be  thrown  into 
the  embankment ;  and  earth,  gravel  or  crushed  rock  will  be  added  sufficient 
to  raise  the  embankment  8  inches  above  the  normal  surface  of  the  street. 


*By  courtesy  of  William  B.  Chase,  City  Engineer. 


628 


BICYCLE   PATHS  AND   RACE   TRACKS,  [CHAP.  XX. 


The  cycle  way  will  be  slightly  crowned.  The  side  slopes  must  be  rammed 
until  they  are  hard  and  smooth;  and  the  top  of  the  path  must  be  rammed 
until  it  is  firm  and  hard.  The  top  will  then  be  covered  with  a  1-inch  layer 
of  cementing-gravel  screenings  *  or  crushed-rock  screenings,  which  will 
be  rolled  until  hard  and  smooth.  The  gutter  next  to  the  curb  must  not  be 
less  than  6  inches  wide  at  the  bottom,  and  must  be  smooth  and  clean. 

"  Plan  C  is  an  earth  cycle  way  with  plank  curb.  This  path  will  be  built 
by  setting  a  4  X  14-inch  curb  5^  feet  from  the  sidewalk  curb.  The  top  of  the 
cycle-way  curb  will  be  2  inches  below  the  top  of  the  sidewalk  curb  and  will  be 
set  in  the  same  manner.     The  joints  in  the  curb  will  be  secured  by  spiking  a 





Fig.  164.— Portland  City-Bicycle  Paths. 

piece  of  3  X  12-inch  plank  4  feet  long  on  the  inside  of  the  curb,  the  top  of 
the  splicing  piece  to  be  2  inches  below  the  top  of  the  curb.  On  the  outside 
of  the  cycle-way  curb  a  ditch  will  be  excavated  approximately  6  inches 
below  the  top  of  the  curb,  the  material  from  the  ditch  being  thrown  on  the 
path.  After  the  curb  is  securely  set  and  tamped,  an  embankment  will  be 
formed  of  earth,  gravel,  or  of  crushed  rock  to  a  height  at  the  center  of  the 
path  of  approximately  8  inches  above  the  normal  surface  of  the  street.  The 
gutter  next  to  the  sidewalk  curb  will  be  6  inches  wide  at  the  bottom,  and  the 


*  Gravel  screenings  having  high  cementing  qualities  were  used,  and  it  is  recog- 
nized that  the  layer  is  thicker  than  is  necessary ;  but  the  material  was  plentiful; 
and  was  used  liberally. 


ART.  1.] 


BICYCLE   PATHS. 


629 


slope  will  be  flat  enough  to  be  stable.  The  embankment  will  be  rammed  or 
rolled  until  it  is  solid.  The  wearing  surface  will  be  a  layer  of  cementing- 
gravel  screenings  or  crushed-rock  screenings,  which  shall  be  rolled  or  rammed 
until  hard. 

"Plan  D  is  the  same  as  Plan  C  except  in  the  matter  of  the  open  gutter 
next  to  the  sidewalk  curb.  The  cycle-way  curb  is  a  4  X  14-inch  plank  set 
5  feet  from  the  sidewalk  curb  with  its  top  edge  1£  inches  below  the  top  of 
the  sidewalk  curb.  The  top  of  the  cycle  way  will  be  finished  with  a  down- 
ward slope  of  1^  inches  toward  the  carriage  way.  Where  considered  neces- 
sary by  the  City  Engineer,  a  tile  drain  must  be  placed  along  the  curb  as 
shown  in  the  Fig.  164;  and  all  house  rain-water  pipes  discharging  into  the 
ditch  must  be  covered  with  earth. 

"  Crossings  will  generally  be  5  feet  wide,  and  will  be  constructed  of  3  X  12- 
inch  fir  planks  laid  on  4  X  4-inch  mud  sills, — the  same  as  is  used  for  sidewalk 
crossings.     For  the  arrangement  of  cycle-way  street-crossings,  see  Fig.  165. 


Fig.  165. — Portland  Cycle-path  Crossing. 


"At  the  lower  corner  of  the  blocks,  the  water  from  the  cycle-way  ditch 
must  be  carried  to  the  ditch  next  to  the  sidewalk  curb  through  a  wooden 
box  constructed  alongside  of  the  cross  walk  and  having  its  top  flush  with 
the  surface  of  the  walk.  The  drain  box  must  not  be  less  than  6X10  inches 
inside,  and  must  be  made  of  3  X  12-inch  plank." 


630  BICYCLE   PATHS  AND   RACE  TRACKS.  [CHAP.   XX. 

978.  For  a  few  particulars  concerning  cycle  ways  constructed 
in  St.  Paul,  Minn.,  see  §  980. 

979.  Cost.  The  cost  of  a  city  cycle  way  will  vary  greatly  with 
the  style  of  construction,  the  cost  of  materials  and  labor,  etc.  The 
following  examples  are  of  interest. 

980.  St.  Paul:  In  St.  Paul,  Minn.,  in  1897,  about  12  miles  of 
cycle  ways  were  built,  the  cost  and  the  method  of  construction 
being  as  follows:  *  A  cycle  way  10  feet  wide  consisting  of  4  inches 
of  coal  cinders  at  the  center  and  2  inches  at  the  side,  and  covered 
with  a  ^-inch  layer  of  sand  and  loam  or  clay  mixed,  having  a  crown 
of  4  inches,  with  broken-stone  street  crossings,  built  where  the  only 
grading  consisted  in  removing  the  sod,  cost  $500  per  mile,  common 
labor  being  18J  cents  per  hour,  teams  37J  cents  per  hour,  and  cin- 
ders 40  cents  per  cubic  yard  delivered.  An  8-foot  path  consisting 
of  cinders  3  inches  deep  at  the  center  and  2  inches  at  the  sides, 
cost  $250  per  mile,  labor  being  15  cents  per  hour,  teams  30  cents 
per  hour,  and  cinders  25  cents  per  cubic  yard  delivered.  A  3-foot 
cinder  path  along  a  graded  street  cost  $165  per  mile. 

981.  Brooklyn.  In  Brooklyn,  N.  Y.,  in  1895,  a  12-foot  cycle 
way  from  Prospect  Park  to  Coney  Island,  constructed  of  broken 
limestone,  cost  about  $3,250  per  mile. 

982.  Rochester.  At  Rochester,  N.  Y.,  a  16-foot  cycle  way  hav- 
ing a  4-inch  limestone  base  and  a  2-inch  trap  top,  cost  practically 
$10,000  per  mile,  exclusive  of  engineering  and  inspection,  labor 
being  $1.50  for  8  hours  and  teams  $3.50  for  8  hours. 

983.  COUNTRY  BICYCLE  PATHS.  As  a  rule,  country  cycle  paths 
are  chiefly  for  pleasure  riding,  and  the  money  available  for  their 
construction  is  limited;  and  consequently  the  severest  economy 
must  be  employed.  A  country  cycle  path  may  be  anything  from  a 
narrow  strip  of  turf  worn  smooth  by  the  passage  of  wheels  or  pedes- 
trians to  a  broad  and  carefully  constructed  roadway. 

984.  Location.  Country  cycle  paths  are  usually  located  at  the 
side  of  the  public  highway,  in  the  West  at  least,  between  the 
side  ditch  and  the  property  line  (see  §  88) ;  and  in  any  case  there 
should  be  a  ditch  between  the  bicycle  path  and  the  carriage  way 
to  prevent  teamsters  from  trespassing  upon  the  former. 

*  L.  W,  Rundlett,  City  Engineer,  in  Proc.  Amer.  Soc.  of  Municipal  Improve- 
ments, Vol.  4,  p.  323. 


AKT.   1.]  BICYCLE    PATHS.  631 

985.  Width.  Length  is  more  important  than  width,  and  conse- 
quently the  path  should  be  made  no  wider  than  is  necessary  to 
accommodate  the  travel.  A  cyclist  touring  alone,  or  several  riding 
in  single  file,  may  ride  swiftly  and  comfortably  on  a  path  only  10  or 
12  inches  wide.  Unless  the  travel  is  considerable,  a  width  from  3 
to  4  feet  is  abundant.  One  rider  can  safely  pass  another  at  speed 
upon  a  path  4  feet  wide. 

986.  Grade.  If  possible  the  grades  should  be  reduced  to  5 
per  cent  or  less,  as  a  steeper  grade  can  not  be  ascended  without 
extreme  effort  and  is  liable  to  cause  accidents  in  descending.  A  2 
per  cent  grade  can  be  ascended  with  comparative  ease  and  be  de- 
scended with  but  little  effort  and  without  serious  danger. 

987.  Cross  Section.  The  surface  of  the  bicycle  path  should  be 
raised  above  the  general  natural  surface  to  afford  drainage.  Usu- 
ally the  excavation  of  a  slight  ditch  on  each  side  of  the  path  will 
furnish  material  sufficient  for  this  purpose.  The  surface  should 
have  a  slight  crown,  that  is,  should  be  a  little  higher  in  the  center 
than  at  the  sides.  On  level  dry  ground  it  is  sufficient  to  have  an 
elevation  of  4  inches  at  the  center  and  2  inches  at  the  sides  where 
the  surface  of  the  path  begins  to  slope  abruptly  to  the  natural  sur- 
face. In  low  wet  places  it  may  be  necessary  to  throw  up  a  low 
embankment  upon  which  to  construct  the  path;  and  on  a  side  hill 
it  is  necessary  to  provide  ditches  of  sufficient  capacity  to  carry  away 
the  storm  water  and  to  prevent  it  from  coursing  down  the  middle  of 
the  cycle  path.  If  the  side  hill  is  steep  in  a  direction  transverse  to 
the  path,  it  will  be  necessary  to  construct  a  catch-water  drain  (see 
§  116)  and  to  build  culverts  under  the  path  at  intervals,  to  prevent 
the  storm  water  from  flowing  over  the  path. 

988.  Construction.  For  a  discussion  of  the  various  materials 
employed  in  constructing  cycle  paths,  see  §  973. 

In  some  cases  the  construction  consists  in  simply  cutting  a  strip 
of  grass  10  or  12  inches  wide  along  the  location  selected,  to  indicate 
the  line  of  the  path  and  to  confine  the  travel,  leaving  the  passing 
wheels  to  make  a  smooth  surface.  In  other  cases  a  path  is  made  by 
turning  a  furrow  with  a  plow  and  raking  down  the  loosened  earth 
at  one  side  of  the  furrow  to  form  a  level  surface  for  the  passage  of  the 
wheels,  which  in  time  will  compact  the  earth  and  make  it  hard  and 
smooth. 


632  BICYCLE    PATHS   AND    RACE   TRACKS.  [CHAP.   XX. 

A  more  elaborate  construction  consists  in  removing  the  sod  and 
spreading  a  layer  of  cinders  3  or  4  inches  thick.  Cycle  paths  are 
not  subjected  to  heavy  loads,  and  hence  do  not  require  a  carefully 
prepared  foundation ;  but  if  the  natural  soil  is  loose  and  porous,  it  is 
better  and  more  economical  of  the  surfacing  material  to  roll  the  sub- 
grade  before  applying  the  cinders.  All  grass,  weeds,  loose  roots, 
etc.,  should  be  removed  from  the  subgrade  before  rolling  it.  The 
cinders  should  be  sprinkled  and  then  rolled  with  a  roller  weighing 
not  less  than  20  pounds  per  linear  inch  of  face.  The  rolling  is 
usually  done  with  a  hand  roller. 

939.  Cost.  Fairly  good  cycle  paths  have  frequently  been  con- 
structed for  $20  per  mile  by  leveling  off  the  rough  places  and  apply- 
ing a  thin  coat  of  cinders  where  most  needed.  Where  there  is  not 
much  grading  required,  a  cinder  surface  2  to  3  feet  wide  will  cost 
about  $100  per  mile. 

In  St.  Paul,  Minn.,  in  1897,  a  6-foot  cycle  path  consisting  of  cin- 
ders 3  inches  deep  at  the  center  and  2  inches  at  the  side,  covered 
with  about  \  inch  of  clay  or  loam  and  a  coating  of  coarse  sand, 
constructed  along  a  country  road  where  the  cinders  were  hauled  an 
average  of  1^  miles,  cost  $200  per  mile.* 

990.  Maintenance.  The  work  of  maintenance  depends  some- 
what upon  the  nature  of  the  material  of  which  the  surface  is  com- 
posed; but  usually  consists  in  (1)  repairing  damages  from  storm 
water  and  trespassers,  (2)  cutting. out  weeds,  particularly  at  the 
edge  of  the  path,  and  lining  up  the  side  to  give  a  neater  appearance, 
(3)  raking  and  rolling  the  surface  of  the  path,  (4)  adding  a  layer  of 
cinders  or  gravel  where  necessary.  The  above  repairs  of  a  cinder 
path  cost  about  $25  to  $30  per  mile,  for  each  time  over  the  path, 
which  is  usually  once  per  year. 

Art.  2.     Bicycle-race  Tracks.! 

991.  With  the  general  introduction  of  bicycles  came  a  relatively 
small  class  of  people  who  choose  bicycle  racing  as  a  recreation  or  ai 
a  profession.     From  these  riders  came  a  demand  for  tracks  built 

*  Proc.  Amer.  Soc.  of  Municipal  Immprovements,  Vol.  4,  p.  323. 

-j-This  article  is  an  abstract  of  the  thesis  of  Horatio  Weber  Baker,  the  author's 
son  and  student,  presented  for  the  Degree  of  Bachelor  of  Science  in  Civil  Engineer- 
ing, University  of  Illinois,  June,  1901.    Manuscript  in  the  University  Library. 


ART.  2.]  BICYCLE-RACE   TRACKS.  633 

especially  for  bicycle  racing.    Although  bicycle  racing  is  attracting 
but  little  attention  at  present,  it  may  not  be  amiss  to  consider 
briefly  the  theory  and  the  practice  of  bicycle  race-track  construe-  ■ 
tion. 

The  design  of  a  track  will  be  considered  under  three  heads:  1, 
the  ground  plan;  2,  the  banking  or  super-elevation  of  the  outer  edge; 
and  3,  the  material  used  in  the  constuction. 

992.  GROUND  PLAN.  The  following  principles  must  be  borne 
in  mind  in  designing  the  ground  plan  of  a  bicycle  race-track. 

1.  The  length  and  the  form  of  the  track  will  depend  upon  the 
size  and  the  shape  of  the  area  available. 

2.  Large  tracks  are  expensive  to  construct,  and  do  not  afford 
the  spectators  as  good  a  view  of  the  races  as  smaller  tracks.  Very 
small  tracks  are  objectionable  because  of  the  sharp  curvature  and 
consequent  high  banking  required. 

3.  For  convenience  it  is  desirable  that  the  length  of  the  track 
shall  be  an  aliquot  part  of  a  mile.* 

4.  The  field  should  not  be  so  wide  that  the  spectators  are  unable 
to  see  easily  all  parts  of  the  race. 

5.  It  is  desirable  that  there  should  be  enough  straight  track 
upon  which  to  start  the  race. 

6.  The  curves  should  be  of  such  form  that  the  rider  experiences 
no  lurch  due  to  a  change  of  direction  in  following  the  curve. 

7.  On  curves  a  super-elevation  of  the  outer  edge  is  required, 
while  on  tangents  none  is  required;  and  since  this  super-elevation 
can  not  be  effected  instantly,  a  varying  curvature  should  be  used  to 
permit  the  joining  of  the  flat  tangents  with  the  fully-banked  curves. 

993.  The  conditions  which  best  meet  the  first  four  requirements 
can  be  determined  only  by  experience,  while  the  conditions  meeting 
the  remainder  can  be  determined  only  by  mathematical  analysis. 
It  is  proposed  to  describe  the  more  noted  tracks  with  a  view  of 
determining  the  present  status  of  the  best  practice,  and  then  to 
design  a  track  which  shall  fully  meet  all  of  the  above  requirements. 

994.  Present    Practice.     The  first  tracks  were  very  crudely 

laid  out.     For  example,  it  is  stated  that  the  curves  of  one  of  the 

earliest  tracks  in  this  country,  the  half-mile  track  at  Hampden 

*  The  length  of  a  bicycle  track  is  measured  on  a  line,  called  the  pole  line  or  pole, 
18  inches  from  the  inner  edge  of  the  track. 


634  BICYCLE  PATHS   AND   RACE   TRACKS.  [CHAP.   XX. 


Park,  Springfield,  Mass.,  were  located  by  running  a  bicycle  over  the 
ground  and  staking  out  the  trail.  Most  of  the  early  tracks  were 
semicircles  connected  by  tangents.  Among  these  are  the  ones  at 
Waltham,  Mass.,  and  Louisville,  Ky.  Each  is  one  third  of  a  mi'e 
in  length  with  semicircles  of  150  feet  radius  and  tangents  409  fev,t 
long.  These  tracks  have  each  held  many  world's  records,  and  were 
for  a  time  very  popular. 

The  Charles  River  track,  Boston,  Mass.,  is  one  third  of  a  mile  in 
length,  the  circular  curves  being  joined  to  the  tangents  by  ease- 
ment curves  consisting  of  compound  circular  arcs.  This  track 
is  a  later  design  by  the  designer  of  the  Waltham  track,  and  may  be 
considered  as  proving,  in  the  mind  of  the  designer  at  least,  the  im- 
portance of  joining  the  tangents  and  the  curves  by  arcs  of  varying 
radii. 

The  track  at  Manhattan  Beach,  Long  Island,  N.  Y.,  constructed 
in  1896,*  seems  to  have  been  the  first  attempt  to  meet  scientifi- 
cally requirements  6  and  7  of  §  992.  This  track  is  one  third  of  a 
mile  in  length,  and  consists  of  two  tangents  connected  by  •  'elliptical 
curves  "  to  circular  arcs — see  Fig.  166,  page  635.  Apparently  the 
''elliptical  curve,"  A  B,  consists  of  a  series  of  nine  circular  arcs, 
each  6°  long,  having  radii  ranging  in  length  from  144  to  212  feet. 
The  circular  arc,  B  C,  is  38°  17'  long,  and  has  a  radius  of  136  feet. 
The  tangents  are  373.47  feet  long,  the  "  elliptical  curves  "  162.4  feet, 
and  the  circular  arcs  181.76  feet.  The  track  is  26.5  feet  wide,  ex- 
cept the  home-stretch,  which  is  40  feet, — the  widest  track  in  this 
country. 

In  1896  a  one-half  mile  track  was  constructed  by  the  West  Park 
Board  in  Garfield  Park,  Chicago.f  Fig.  167,  page  636,  shows  the 
ground  plan  of  this  track.  The  tangents  are  376.5  feet  long  and 
are  connected  by  semicircles  having  a  radius  of  300.32  feet.  The 
width  is  25  feet,  except  upon  the  home-stretch,  where  it  is  35  feet. 
The  widening  of  the  home-stretch  was  accomplished  by  moving  the 
center  of  the  semicicular  arc  for  the  outside  of  the  track  10  feet 
toward  the  home-stretch. 

In  1897  a  quarter-mile  track  was  constructed  at  Racine,  Wis., 


*  Engineering  News,  Vol.  35,  p.  188-89. 

t  Jour.  Western  Society  of  Engineers,  Vol.  IV.,  p.  224-25. 


ART.  2.] 


BICYCLE-RACE   TRACKS. 


635 


636 


BICYCLE   PATHS   AND   KACE  TRACKS.  [CHAP.  XX. 


ART.   2.  J 


BICYCLE-RACE    TRACKS. 


637 


of  the  same  ground  plan  as  the  Manhattan  .track  except  that  the 
tangents  were  shortened  and  a  higher  banking  was  used.* 

These  examples  represent  the  most  advanced  theory  of  the  form 
of  bicycle-race  tracks,  since  almost  all  others  have  been  built  by 
carpenters  or  professional  riders  without  reference  to  the  princi- 
ples involved. 

995.  Ideal  Form.  The  length  and  the  form  of  the  track  will 
depend  upon  the  size  and  the  shape  of  the  area  available.  These 
factors  will  vary  so  greatly  that  they  can  not  be  considered  in  a 
general  design;  and  hence  it  will  be  assumed  that  the  area  availa- 
ble is  unlimited. 

For  obvious  reasons  the  length  should  be  an  aliquot  part  of  a 
mile;  and  the  best  authorities  claim  that  on  the  whole  a  track  hav- 
ing four  laps  to  the  mile  is  most  preferable.  Therefore  a  design  will 
be  made  for  a  one-quarter  mile  track. 

996.  Proportions  of  the  Field. — To  determine  the  relation  be- 
tween the  length  anjd  the  breadth  of  the  field  of  those  tracks  which 
may  be  considered  as  the  best  representatives  of  current  practice, 
Table  65  was  computed.  A  study  of  these  data  shows  that  a  track 
to  meet  the  requirements  of  current  practice  should  have  a  field 
about  twice  as  long  as  wide,  or  a  width  of  field  about  one  fifth 
of  the  length  of  the  track.  A  field  of  these  proportions  will  give 
a  track  affording  the  spectators  a  good  view  of  all  parts  of  the 

raee= 

TABLE  65. 

Proportions  op  Field  Representative  of  the  Best  Current 

Practice. 

Arranged  in  the  Order  of  Roundness. 


Ref. 

No. 


Name  of  Track. 


Garfield  Park.. 
Racine.  ..... 

Hawley  f 

Waltham  J... . 
Manhattan.  .  . 


Length 
of  Field. 


976.5 
499.6 
519.6 
709.0 
715.5 


ft. 


Width 
of  Field. 


600  ft. 
295  " 
275  " 
300  l! 
295  '; 


Ratio. 


0.61 
0.59 
0.53 
0.42 
0.41 

0.51 


Le»gth 
of  Track. 


2640  ft. 
1320  " 
1320  " 
1760  u 
1760  " 


Width 
of  Field. 


600  ft. 
295  " 
275  " 
300  " 
295  " 


mean 


Ratio. 


0.23 
0.22 
0.21 
0.17 
0.17 

0.199 


*Jour.  Western  Society  of  Engineers,  Vol.  4,  p.  225-27. 

f  Recommended  by  Mr.  C.  E.  Hawley,  Sing  Sing,  N.  Y.,  the  recognized  authority 
on  bicycle  tracks,  in  a  private  communication  to  the  author. 
|  Same  as  the  track  at  Louisville. 


638 


BICYCLE    PATHS   AND    RACE    TRACKS.  [CHAP.   XX. 


997.  Form  of  Curves.  The  track  should  gradually  change  from 
the  straight  line  to  the  maximum  curvature  in  order  that  the  rider 
may  experience  no  lurch  in  going  from  the  straight  to  the  curved 
portions.  If  in  Fig.  168  the  full  line  ABODE  represents  a 
portion  of  the  pole  line  of  a  track  consisting  of  semicircles  con- 
nected by  tangents,  a  racer  riding  in  the  direction  indicated,  upon 
arrival  at  B,  the  point  of  tangency,  will  not  be  able  to  change  in- 
stantly from  a  straight  path  with  an  infinite  radius  to  a  curved  path 
with  a  uniform  finite  radius,  but  will  involuntarily  take  a  curvi- 
linear course  having  a  uniformly  decreasing  radius.  The  dotted 
line  of  Fig.  168  shows  the  path  involuntarily  taken  by  the  rider. 


Fig.  168. 

Similarly  in  entering  a  tangent  from  a  curve,  the  rider  will  swing 
out  from  the  pole  line  of  the  tangent  in  a  curve  of  increasing  radius. 
Since  the  distances  are  measured  on  the  pole  line,  and  since  all  ex- 
cess distance  ridden  adds  to  the  time  of  the  race,  there  is  a  decided 
advantage  in  having  the  pole  line  of  the  same  curvature  as  that 
of  the  path  naturally  taken  by  the  rider.  Further,  the  greatest  ease 
with  which  a  wheel  can  be  guided  around  a  curve  of  gradually 
varying  radius  also  adds  to  the.  speed  of  the  race. 

Again,  the  outer  edge  of  the  track  on  curves  should  be  higher 
than  the  inside,  to  neutralize  the  effect  of  centrifugal  force ;  and  this 
super-elevation  should  vary  inversely  as  the  radius  of  curvature. 
Since  it  is  impossible  to  change  instantly  from  flat  tangents  to 
banked  curves,  a  track  consisting  of  semicircles  and  tangents  will 


ART.  2.] 


BICYCLE-RACE   TRACKS. 


639 


not  permit  the  proper  super-elevation  of  the  outer  edge,  but  if  the 
tangent  is  connected  to  the  circular  arc  by  a  curve  of  uniformly 
varying  curvature,  the  banking  required  increases  gradually  from 
zero  on  the  tangent  to  the  full  amount  at  the  beginning  of  the 
circular  arc. 

This  condition  is  approximated  by  joining  the  tangent  and  the 
circular  curve  by  circular  arcs  of  decreasing  radii,  as  in  the  Man- 
hattan track,  Fig.  166,  page  635;  but  this  condition  is  fully  and 
more  simply  met  by  using  the  transition  spiral  (see  §  429). 

Fig.  169,  page  640,  shows  a  one-fourth  mile  bicycle  track  each 
quadrant  of  which  consists  of  a  tangent  30  feet  long,  a  transition 
spiral  160.18  feet  long  and  a  circular  arc  139.82  feet  long,  making  a 
total  length  of  330  feet  for  one  quadrant  or  1,320  feet  for  the  com- 
plete circumference.  The  circular  arcs  may  be  laid  out  by  any  of  the 
methods  described  for  Horse-race  Tracks  in  Art.  2,  Chapter  VII, 
pages  278-92.  The  transition  spiral  may  be  laid  out  in  either  of 
two  ways,  namely:  (1)  by  deflection  angles  from  the  initial  tangent 
and  by  chords  measured  along  the  curves ;  or  (2)  by  offsets  from  the 
tangent  prolonged.  Tables  66  and  67  give  the  data  for  laying  out 
the  spiral  by  the  two  methods  just  mentioned,  respectively. 


TABLE  66. 

Chords  and  Deflection  Angles  for  Locating  the  Transition  Spiral 
for  the  Inside  Edge  of  a  Quarter-mile  Bicycle  Track. 


Ref. 

No. 


Point  on 
Spiral. 


Distance  from 

theP.S.  along 

the  Curve. 


Deflection  Angle 

at  the  P.  S.  from 

the  Initial 

Tangent. 


P.S. 

1 

2 
3 
4 
5 
6 
5.  C 


c. 


0.00  Feet 

25.0 

50.0 

75.0 
100.0 
120.0 
140.0 
158.47 


0° 
0° 
1° 
2° 
4° 
6° 
8° 
10° 


00' 
16'.  3 
5'. 2 
27'.  0 
21'. 0 
15'.  6 
30'.  7 
53'.  7 


The  field  of  the  track  shown  in  Fig.  169  is  0.59  as  wide  as  long, 
and  is  a  little  nearer  round  than  the  mean  of  the  tracks  in  Table  65, 
page  637 ;  but  if  the  field  were  made  narrower,  the  curvature  would 
be  sharper,  and  curves  with  a  large  radius  are  of  more  importance 


640 


BICYCLE    PATHS   AND    RACE   TRACKS.  [CHAP.   XX. 


ART.  2.] 


BICYCLE-RACE   TRACKS. 


641 


than  a  narrower  field.  The  above  design  meets  all  the  require- 
ments stated  in  §  992  and  also  possesses  some  important  features 
new  in  bicycle-race  track  construction. 

TABLE  67. 

Rectangular  Coordinates  for  Locating  the  Transition  Spiral  for  the 
Inside  edge  of  a  Quarter-mile  Bicycle  Track. 


Ref. 
No. 

Point  on 
Spiral. 

Distance  from 
P.  S.  on  the  Tan- 
gent Prolonged. 

Offset  Perpen- 
dicular to  the 
Tangent. 

1 
2 
3 
4 
5 
6 
7 
8 

P.  s. 

1 

2 
3 
4 
5 
6 
P.  C.  C. 

0 .  00  Feet 

25.00    " 

49.98    " 

74.88    " 

99.48    " 

118.71    " 

137.18    " 

153.20    " 

0.00  Feet 

0.12    " 

0.95    " 

3.20    " 

7.57    " 

13.03    " 

20.55    " 

29.52    " 

998.  SUPER-ELEVATION.  If  a  man  attempts  to  ride  a  bicycle 
around  a  curve,  the  rider  and  the  wheel  must  lean  inward  to  bal- 
ance the  centrifugal  force;  and  if  the  surface  of  the  track  is  level 
transversely,  the  wheel  will  not  be  perpendicular  to  the  surface  and 
will  tend  to  run  in  a  curve,  which  may  have  a  greater  or  a  less  radius 
than  that  of  the  track,  and  consequently  increased  attention  and 
effort  will  be  required  in  guiding  the  wheel.  Further,  if  the  in- 
clination of  the  wheel  is  considerable,  there  is  a  tendency  for 
it  to  slip  on  the  surface.  If  the  outside  of  the  track  is  elevated  on 
the  curves  so  that  the  wheel  is  always  perpendicular  to  the  surface, 
then  the  wheel  has  a  tendency  to  continue  in  a  straight  line,  and  only 
a  minimum  effort  is  required  in  guiding;  and  consequently  the 
whole  attention  may  be  given  to  securing  speed. 

Equation  (2),  page  290,  shows  the  relation  that  should  exist  be- 
tween the  super-elevation  or  banking,  and  the  speed  and  the  radius 
of  the  curve.*     Having  the  design  of  the  ground  plan,  the  radius  of 


*  Strictly  speaking  the  R  in  this  formula  should  not  bo  taken  as  the  radius  of 
the  pole  line,  but  as  the  radius  of  the  curve  described  by  the  center  of  gravity  of 
the  rider  and  the  wheel,  which  will  be  a  little  less  than  the  radius  of  the  pole  line 
owing  to  the  inward  inclination  of  the  wheei  and  rider*,  but  such  refinement  is 
unnecessary. 


642  BICYCLE    PATHS   AND    KACE    TRACKS.  [CHAP.    XX. 

curvature  will  be  known;  but  since  the  banking  depends  upon  the 
velocity,  the  track  must  be  designed  for  some  particular  speed.  In 
deciding  upon  the  velocity  to  be  adopted,  it  is  necessary  to  deter- 
mine whether  the  maximum  or  mean  velocity  shall  be  employed. 
If  the  track  is  to  be  used  chiefly  for  races  ridden  against  time,  the 
maximum  velocity  should  be  adopted ;  but  if  the  track  is  to  be  used 
chiefly  for  miscellaneous  racing,  the  super-elevation  should  be  de- 
signed for  the  average  velocity.  To  determine  the  practice  in  this 
respect,  the  banking  of  the  more  noted  tracks  will  be  investigated. 

In  the  early  tracks  high  banking  seems  to  have  been  avoided  for 
two  reasons:  first,  because  of  a  baseless  prejudice  against  it;  and 
second,  because  many  of  the  races  ridden  in  competition  were  so 
slow  as  not  to  require  high  banking.  Recently  the  speed  has 
increased,  and  motor  pacing  has  become  prevalent;  and  hence 
higher  banking  is  more  common. 

The  curves  of  the  Louisville  and  of  the  Walt  ham  tracks  have  a 
banking  such  that  at  a  speed  of  a  mile  in  2  minutes  and  53  seconds 
the  wheel  is  normal  to  the  surface.  The  super-elevation  of  the 
Manhattan  track  was  computed  for  a  speed  of  a  mile  in  2  minutes 
and  32  seconds.  Fig.  166,  page  635,  shows  the  banking  of  this 
track,  expressed  in  degrees  with  the  horizontal.  The  curves  of  the 
Racine  track, which  have  the  same  radii  as  the  Manhattan  track, are 
banked  for  a  speed  of  a  mile  in  2  minutes  and  26  seconds — a  trifle 
higher  speed  than  for  the  Manhattan  track.  The  banking  of  the 
Garfield  Park  track  was  computed  for  a  speed  of  a  mile  in  2  minutes. 
The  angles  of  the  super-elevation  of  this  track  are  shown  in  Fig.  167, 
page  636.  It  is  stated  that  Johnson  in  1896  on  this  track,  in  making 
a  world's  record  of  a  mile  in  1  minute  and  49  seconds,  leaned  slightly 
toward  the  inside  of  the  track.  Since  the  banking  was  figured  for  a 
2-minute  gait,  the  rider  going  at  a  speed  of  1  minute  and  49  seconds 
would  be  compelled  to  lean  toward  the  center  of  the  track  to  bal- 
ance the  centrifugal  force,  which  shows  in  a  crude  way  the  agree- 
ment of  theory  and  practice. 

Many  short  wooden  tracks  have  been  constructed  with  very 
high  banking.  Notable  among  these  is  a  sixth  of  a  mile  track 
opened  in  Springfield,  Mass.,  in  July,  1900.  The  curves  (appar- 
ently semicircles)  are  banked  for  a  speed  of  a  mile  in  1  minute  and 
20  seconds,  the  inclination  of  the  surface  on  the  curves  being  48°, 


ART.  2.] 


BICYCLE-RACE   TRACKS. 


64S 


and  on  the  tangents  30° — the  steepest  track  known.    This  track  is 
pronounced  by  racing  men  to  be  the  fastest  in  the  world. 

A  summary  of  the  speeds  for  which  the  various  tracks  were  con- 
structed is  shown  in  Table  68. 

TABLE  68. 
Speed  for  which  the  Banking  of  Different  Tracks  was  Constructed. 


Ref. 
No. 

J 
Name  of  Track. 

Speed. 

Feet  per 
Second. 

Time  for  1  Mile. 

1 

2  | 

3  j 

4   i 

5  i 

Waltham  * 

Manhattan 

30.53 
34.24 
36.17 
44.00 
66.00 

2  min.  53  sec. 
2    "     34   " 
2    "     26  " 
2    "     00  " 
1    "     20  " 

Racine 

Garfield 

Springfield,  Mass.  .  .  . 

*  Same  as  the  track  at  Louisviile. 

999.  It  is  obvious  that  the  choice  of  the  velocity  to  be  used  in 
computing  the  super-elevation  depends  upon  experience  and  judg- 
ment, and  not  upon  mathematical  relations.  If  the  track  is  to  be 
used  for  motor  racing  without  competition,  the  velocity  should  be 
high,  perhaps  66  feet  per  second,  or  a  mile  in  1  minute  and  20  sec- 
onds; but  if  the  track  is  to  be  used  for  races  of  competition  without 
motor  pacing,  this  velocity  should  be  about  44  feet  per  second,  or  a 
mile  in  2  minutes. 

The  values  shown  in  Fig.  169,  page  640,  were  computed  for  a 
velocity  of  48  feet  per  second,  or  a  mile  in  1  minute  and  50  seconds. 
Should  the  speed  vary  materially  from  this  value,  the  wheel  will  not 
stand  exactly  normal  to  the  surface,  and  hence  may  have  a  tendency 
to  slip ;  but  the  tires  of  a  bicycle  will  not  slip  unless  the  angle  be- 
tween the  plane  of  the  wheel  and  the  normal  to  the  track  is  greater 
than  the  angle  of  repose.  Experiments  show  that  the  angle  of  re- 
pose for  a  bicycle  rubber-tire  sliding  on  a  dry  cement  sidewalk  is 
23°  15',  and  practically  the  same  value  for  a  smooth  dry  wooden 
surface.  For  macadam,  cinders,  gravel,  etc.,  the  angle  of  repose  is 
considerably  more  than  the  above.  Therefore  there  will  be  no 
danger  of  the  wheel's  slipping,  if  the  speed  be  increased  until  the 
wheel  leans  nearly  23°  outside  of  the  normal  to  the  track,  or  if  the 
speed  be  decreased  until  the  wheel  inclines  nearly  23°  inside  of  the 


644  BICYCLE    PATHS   AND    RACE   TRACKS.  [CHAP.   XX. 


normal.  For  the  track  shown  in  Fig.  169,  page  640,  the  first  posi- 
tion of  the  wheel  corresponds  to  a  speed  of  a  mile  in  1  minute  and 
12  seconds,  and  the  second  to  a  mile  in  4  minutes  and  53  seconds. 
The  former  is  the  speed  of  the  fastest  steam-motor  cycle,  and  the 
latter  is  lower  than  any  probable  bicycle  race.  Therefore  if  the 
super-elevation  of  the  track  shown  in  Fig.  169  is  adjusted  for  a 
speed  of  48  feet  per  second,  or  a  mile  in  1  minute  and  50  seconds,  it 
can  be  used  for  considerably  faster  races,  and  still  be  safe  for  slow 
races  and  amateur  riding.  However,  it  will  not  be  possible  to 
attain  the  highest  speed  unless  the  super-elevation  is  adjusted 
approximately  for  that  speed,  since  otherwise  part  of  the  rider's 
attention  and  effort  is  required  to  balance  his  wheel. 

1000  It  is  the  practice  of  some  designers  to  compute  the  banking 
for  one  speed,  and  then  construct  the  track  with  an  arbitrary, 
fractional  part  of  the  computed  value.  For  example,  the  banking 
of  the  Manhattan  track  was  computed  nominally  for  a  2-minute 
speed,  and  then  constructed  with  a  super-elevation  equal  to  60  per 
cent  of  the  computed  value.  The  actual  banking  is  that  required 
by  a  2  minute  and  34  seconds  speed. 

1001.  It  has  been  proposed  to  make  the  surface  of  a  bicycle- 
race  track   on  curves  concave  as  shown  in  Fig.   170.     In  other 


Fig.  170. — Concave  Surface  of  Bicycle-race  Track. 

words,  it  has  been  proposed  to  make  the  angle  of  inclination  of  the 
surface  of  the  track  greater  at  the  outer  edge  than  at  the  pole 
line.  The  claim  is  that  such  a  surface  would  make  it  easier  for  one 
rider  to  pass  another,  since  to  accomplish  this  he  must  ride  at  a 
higher  speed  and  hence  would  require  a  steeper  inclination.  This 
conclusion  is  wrong,  since  the  effect  of  the  increased  radius  of  curva- 
ture almost  exactly  counteracts  the  effect  of  the  increased  velocity 
(see  equation  (2),  page  290).  It  is  also  claimed  that  the  concave 
surface  would  prevent  a  rider  from  flying  off  the  tracks,  should  he 
momentarily  lose  control  of  his  wheel.  This  advantage  is  not 
important,  since  the  banking  is  sufficient  of  itself  to  prevent  such 
an  accident.     However,  the  concave  surface  would  be  an  advantage 


ART.  2.]  BICYCLE-RACE   TRACKS.  645 

on  a  track  having  low  banking.  A  third  objection  to  the  concave 
surface  is  that  it  would  be  more  expensive  to  construct.  On  the 
whole,  a  straight  surface  is  probably  the  better. 

The  tendency  to  "fly  the  track"  may  be  lessened  by  painting 
parallel  guide  lines  on  the  surface  of  the  track.  This  feature  was 
used  on  the  Manhattan  track  as  described  more  in  detail  in  §  1003. 

1002.  MATERIALS  OF  CONSTRUCTION.  The  surface  of  a 
bicycle-race  track  may  be  loam,  clay,  cinders,  wood,  or  cement. 

Most  of  the  early  tracks  were  constructed  of  either  loam  or  clay. 
Such  surfaces  are  cheap  and  easy  to  construct;  but  on  the  other 
hand,  (1)  the  cost  of  maintenance  is  great,  (2)  high  banking  can 
not  be  used,  and  (3)  moisture  destroys  temporarily  the  usefulness  of 
the  track.  The  Hampden  Park  track  was  constructed  of  clay  cov- 
ered with  a  thin  layer  of  brick  dust,  and  at  one  time  was  very 
popular,  owing  chiefly  to  its  excellent  surface. 

A  surface  of  cinders  is  very  cheap  and  easy  to  construct,  and  is 
not  affected  by  moisture;  but  cinders  can  not  be  used  with  high 
banking,  and  such  a  surface  is  expensive  to  maintain,  and  wounds 
received  by  a  rider  in  falling  often  prove  serious. 

A  well  constructed  wooden  surface  is  very  fast,  and  for  this 
reason  has  been  used  in  many  short  tracks,  in  which  high  banking 
is  required.  An  example  of  such  construction  is  the  Colosseum  track 
at  Springfield,  Mass.  The  surface  consists  of  strips,  one  inch  square, 
nailed  to  a  foundation  of  2"  X 10"  timbers.  In-doors,  where  tracks 
are  frequently  constructed  for  temporary  use,  wood  has  decided 
advantages ;  but  for  out-door  use  wooden  tracks  are  uneconomical, 
because  of  the  destructive  action  of  the  elements. 

In  most  of  the  larger  tracks  lately  constructed,  cement  surfaces 
have  been  used.  Such  a  surface  is  practically  indestructible,  and 
hence  there  is  no  expense  for  maintenance.  Its  usefulness  is  not 
destroyed  by  moisture,  and  any  degree  of  smoothness  may  be  ob- 
tained. Cement  was  used  in  the  construction  of  the  Waltham,  the 
Louisville,  the  Manhattan,  the  Garfield  Park,  and  the  Racine  tracks. 
The  surface  of  the  Manhattan  track  is  most  nearly  ideal  and  for  that 
reason  will  be  described  somewhat  in  detail.  As  is  shown  in  Fig. 
171,  page  646,  the  embankment  of  the  Manhattan  track  is  com- 
posed of  four  distinct  layers:  1,  a  gravel  embankment;  2,  an  8-inch 
layer  of  ash  concrete ;  3,  a  3-inch  layer  of  crushed  granite  concrete ; 


646  BICYCLE   PATHS  AND   RACE  TRACKS.  [CHAP.  XX. 

and,  4,  a  top  layer  of  1 J  inches  of  cement  mortar.  The  gravel  was 
deposited  in  thin  layers  and  thoroughly  compacted  by  rolling.  The 
ash  concrete,  whose  purpose  is  to  protect  the  gravel  embankment 
from  washouts  and  from  injury  by  frost,  consists  of  Portland  cement 
and  ashes  in  the  ratio  of  1  to  8  or  10.  The  3-inch  layer  of  granite 
concrete  is  composed  of  one  part  of  sand,  one  part  of  Portland 
cement,  and  seven  parts  of  crushed  granite.  The  top  layer  consists 
of  1J  inches  of  mortar  composed  of  one  part  Portland  cement,  one 
part  sand,  and  two  parts  of  powdered  granite.      Lampblack  was 

J)k  Cement 
3' 'Granite  Concrvte^^  ^^^'Ash  Concrete 

6 'Ash  Concrete 


Fig.  171. — Cross  Section  of  Manhattan  Bicycle-race  Track. 

mixed  with  the  cement  mortar  to  prevent  the  glare  of  the  sun.  The 
surface  of  the  mortar  was  roughened  by  special  tools  to  prevent  the 
slipping  of  the  tires.  Special  care  was  taken  that  the  interstices 
between  the  blocks  of  concrete  should  not  be  so  wide  as  to  impart  a 
vibration  to  the  bicycle.  The  surface  of  this  track  has  withstood  the 
test  of  actual  service,  as  well  as  the  weathering  of  several  years, 
and  has  proved  itself  very  satisfactory. 

1003.  A  novel  feature  of  this  track  is  the  four  parallel  black 
guide-lines,  each  four  inches  wide,  painted  on  the  surface  of  the 
track.  A  racer  riding  at  full  speed  with  his  head  bent  down  over 
the  handle  bars  does  not  notice  that  he  is  approaching  the  curve, 
and  if  he  does  not  guide  his  wheel  accordingly  he  will  run  off  the 
track.  The  guide-lines  warn  him  as  he  approaches  the  curves  and 
thus  prevent  an  accident. 


INDEX. 


ABR— ASP 

Abrasion  test  for  road  stone,  181,  182,  186, 

187 
Abrasion  testing  machine,  182 
Absorption  test  for  road  stone,  189 
Asphalt,  Bermudez,  393 
California,  394 
chemical  composition.  388 
Colorado,  396 
cost  of,  433 
definition.  385 
crude.  386 
refined,  386 
rock,  386 
European.  396 
general  characteristics,  387 
Kentucky,  396 
location  of  mines,  391 
nomenclature,  385 
origin  of,  390 
physical  properties,  390 
Texas,  396 
Trinidad,  391 
Utah, 396 
walk,  see  Sidewalk. 
Asphalt-block  pavement,  see  Asphalt  pave- 
ment. 
Asphalt  macadam,  452 
Warren's  method,  452 
Whinery's  method,  453 
Asphalt  mastic,  386 
Asphalt  pavement,  386,  397 

amount  in  U.  S.,  293 
Asphalt  pavements,  artificial  sheet,  defined, 
397 
asphaltic  cement,  401 
adhesiveness,  409 
ammonia,  effect  of,  409 
chemical  composition,  404 
cohesion,  410 
consistency.  406 

variations  with  age,  408 
variations  with  temperature,  407 
mixing,  404 
softening  agent,  401 

asphalt-petroieum  residuum,  403 
maltha,  404 

paraffin-petroleum  residuum,  402 
Pittsburg  flux,  403 
stability  at  high  temperature,  408 
testing,  404 
water,  effect  of,  409 
binder  course,  399 
cost,  432 
asphalt,  433 


ASP 

Asphalt  pavements,  artificial  sheet,  cost  of 
construction   434 
maintenance,  437 
Buffalo,  440,  441 
forty-two  cities.  438,  439 
New  York  City,  441 
Washington.  442 
cross  section,  444 
crown  in  various  cities,  348 
cushion  coat,  401 
defined,  397 
failures,  causes  of,  420 

improper  manipulation.  422 
chilled  cement,  424 
damp  foundation  424 
high  heat,  423 
improper  consistency,  423 
inadequate  compression,  424 
inadequate  mixing.  424 
insufficient  bitumen,  423 
rich  binder.  424 

separation  of  sand  and  cement ,  424 
natural  causes,  425 
bonfires,  428 
cracks,  427 
decay,  425 
illuminating  gas,  426 
leaky  joints,  426 
ordinary  wear,  425 
porous  foundations,  425 
shifting  under  traffic,  428 
weak  foundation,  425 
unsuitable  materials,  421 
asphalt,  421 
flux  421 
free  oil.  422 
sand,  422 
foundation  for,  398 
history,  397 
maximum  grades.  445 
merits  and  defects,  445 
repairing,  method  of,  429 
cracks,  430 
disentegration,  429 
formation  of  waves.  429 
painting  gutters  430 
settlement  of  subgrade.  429 
using  old  material,  431 
repairs,  method  of  recording,  430 
price  of.  443 
specifications  for,  431 
sand,  410 
fineness,  413 
wearing  coat,  414 

647 


648 


INDEX. 


ASP— BKI 

Asphalt  pavement,  artificial  sheet,  laying, 
416 
mixing  cement  and  sand,  415 
rolling,  417,  419 
smoothing  irons,  418 
tamping  irons,  417 
Asphalt  pavement   block,  447 
blocks,  448 
cost,  448 
cost,  451 
durability,  451 
foundation,  449 
merits  and  defects,  451 
specifications,  449 
Asphalt  pavement,  natural  rock,  446 

construction,  447 
Asphalte  camprime.  defined,  387 
Asphalte  oolite" ,  defined,  387 
Asphaltic    cement,    defined,   386;    see   also 

Asphalt  pavements. 
AsDhalt  walk,  592 
block,  593 
sheet.  592 
Australian  woods  for  pavements.  549 
Axles,  effect  of  equal,  on  roads,  128 
Axle  friction,  21 

Belgian  blocks,  defined.  529;  see  also  Stone 

blocks. 
Belgian   pavement,   defined,   529;  see   also 

Stone-block  pavement. 
Bermudez  asphalt,  393 
Bicycle  path.  624 
city,  624 

Brooklyn.  630 

cross  section,  626 

cost,  630 

grade.  626 

examples,  626 

location,  625 

material.  625 

Portland   627 

Rochester.  630 

St.  Paul.  630 

width  625 
country,  630 

construction,  631 

cost,  632 

cross  section,  631 

grade,  631 

location.  630 

maintenance.  632 

St.  Paul.  632 
Bicycle  race  track,  632 
ground  plan.  633 
ideal  form   637 

curves,  638 

proportions  of  field,  637 
materials,  645 
present  practice,  633 

Charles  River,  634 

Hampden  Park.  634 

Garfield  Park.  634 

Manhattan  Beach.  634 

Racine,  634 
super-elevation,  641 
Binding  power  of  road  stone,  178 
Bitumen   385 

Boston,  crown  of  pavements  in,  348 
Bowen  penetration  apparatus,  406 
Brick,  paving  defined.  462 
clay,  463 

chemical  composition.  463 

physical  properties,  465 


SRI 

Brick,  paving,  form,  469 
buttons,  471 
grooves,  471 
raised  letters,  471 
round  corners,  470 
manufacture,  465 
burning,  467 
molding.  466 
re-pressing,  467 
number  per  square  yard,  518,  519 
number  set  per  day,  520 
requisites  for,  472 
size,  468 
testing,  472 

absorptive  power,  475 
appearance,  472 
color,  473 

crushing  strength.  475 
impact  and  abrasion,  481 
Orton's  method,  481 
N.  B.  M.  A.  standard,  482 
Talbot's  method,  481 
Talbot- Jones  method,  488 
service  test,  493 
specific  gravity,  474 
transverse  strength,  479 
Brick  crossing,  598 
paved  street.  599 
unpaved  street,  598 
Brick  pavement,  amount  in  U.  S.,  293 
as  an  arch,  512 
construction   494 
cushion  layer,  497 

template  for,  499 
laying  500 
delivery,  500 
direction  of  courses,  502 
at  street  intersectionsv503 
filling  joints   506 
cement,  508 
patent  fillers,  511 
sand   506 
tar,  507 
inspecting,  505 
setting  504 
rolling,  505 
cost,  516 
brick.  517 
concrete  517 
grading   517 
•hauling,  518 
rolling   517 
setting  520 
summary,  521 
cross  section,  495  496 
crown  for  in  various  cities,  348 
grades,  515 
guarantee   523 
history.  462 
maintenance.  522 
merits  and  defects  516 
rumbling  511 

effect  of  cold  weather,  514 
effect  of  hot  weather  511 
expansion  cushion   515 
tractive  resistance.  29,  31 
Brick  walk   593 
brick,  594 

direction,  596 
laying  597 
cost.  601 
foundation   594 
merits  and  defects.  602 
transverse  slope,  598 


INDEX. 


049 


BRI— BRO 

Bridgeport  thin  macadam  roads  at,  208 
Bridges,  123 

Bridle  paths,  see  Equestrian  roads. 
Broken  stone  for  road  making   177 

characteristics  and  distribution  of  road 
stone,  190 
chert,  193     ■ 
felsite,  194 
field-stones,  193 
granite,  191 
limestone,  192 
sandstone,  193 
shale,  194 
slate,  194 
trap.  191 
cost  of,  236 
crushing,  236 
quarrying,  234 
crusher,  214 
gyratory,  215 
oscillatory,  214 
crushing,  213 

arrangement  of  plant,  216 
cost,  236 
price,  236 

requisites  for  road  stone,  177 
cementing  power,  178 
hardness,  178 
toughness,  178 
sizes,  217 

testing,  methods  of,  180 
abrasion,  181.  182 

Dorrey  machine,  182 
absorption,  189 
cementation,  185 

machine  for  testing,  188 
crushing  test,  189 
impact,  181,  182 
Deval  machine   183 
Broken- stone  road,  177 
agents  of  destruction  242 
decomposition  of  stone,  244 
frost,  244 
horses'  feet,  242 
rain   244 
tracking  243 
wheels  242 
wind. 243 
amount  of  wear.  245 
binding  the  stone.  229 
amount  of  binder  233 
applying  the  binder,  230 
nature  of  the  binder,  229 
Bridgeport,  Conn..  208 
cost  of  construction.  234 
Massachusetts,  240 
New  Jersey.  240 
New  York,  241 
crushing  236,  237 
finished  road,  240 
hauling,  238 
rolling,  239 
setting  telford  236 
spreading,  238 
spi inkling,  238 
cross  section.  209 

examples  of,  209  210,  211 
crown    199 

amount  of.  202 

at  Providence,  202 
effect  on  cleaning  203 
definition,  177 
earth  shoulders.  199 
economics  of,  260 


BRO— CEM 

Broken-stone  road,  forms  of  construction, 
195 
forms  of  subgrade    197 
form  of  profile,  200 
curved.  200 
two  planes,  201 
grade,  maximum,  62 

minimum,  65 
level  for  testing  crown,  204 
Macadam's  form,  177,  196 
macadam  vs.  telford,  196 
maintenance,  241 
cost  of.  257 
Boston,  258 
Chicago,  258 
France,  259 
method  of,  247 
re- coating,  256 
re-grading,  255 
re-surfacing,  255 
work  of,  248 
drainage,  252 
patching,  252 
raveling,  248 
removal  of  mud.  251 
rolling,  250 
ruts,  249 
sprinkling,  250 
modern  telford,  198 
preparing  subgrade.  211 
rolling  the  stone,  226 

amount  required,  227 
setting  the  telford,  212 
shrinkage  in  rolliner,  220 
spreading  the  stoi.e,  218 
Telford's  form,  177,  196,  198 
telford  vs.  macadam,  196 
thickness,  205 

Bridgeport,  Conn.,  208 
formula  for,  207 
tractive  resistance,  22,  24,  25,  26,  28,  29 

31 
width,  198 
wings,  208 
Broken-stone  vs.  gravel  road,  173 
Buck   Hill    gravel,  characteristics  of,  156, 
157,  159 

California  asphalt,  394 
Catch  basin,  336 
construction,  336 
Champaign,  337 
Milwaukee,  339 
Providence,  338 
St.  Pancras,  339 
form  of  cover,  340 
inlet,  340 
location,  339 
Cement,  asohaltic,  386;    see  also   Asphalt 

paveir  ->nts. 
Cement  wa,k,  602 
base,  603 

Portland  vs.  natural,  610 
color,  011 
cost,  615 
expansion,  609 
forms,  603 
foundation,  602 
transverse  slope:  610 
slipperiness,  613 
wearing  coat,  604 
Cementation  test  of  road  stone,  185,  186 

187 
Cementing  power  of  road  stone,  178 


650 


INDEX. 


CEN-CUR 

Census  of  traffic,  567 

Canada.  571 

England.  571 

United  States.  567 
Charcoal  road.  275 

Chert  for  broken-stone  road,  151,  193 
Chicago ,  crown  of  pavements  in,  348 
Cinder  walk,  616 
Coal-slack  roads.  273 
Coal-tar  pavements,  454 

cost  of  construction,  456 
maintenance.  457 

specifications.  455 
Coal  -tar  roads.  454 
Cobble-stone  hammer.  527 
Cobble-stone  pavement,  amount  in  U.  S., 
293 

cost.  527 

cross  section.  525 

grading  for.  526 

merits  and  defects,  527 

stones.  526 
setting.  526 
Cobble-stone  rammer.  527 
Colorado  asphalt.  396 
Concrete,  asphaltic.  defined,  387 

bituminous.  383 

hydraulic.  367 
cost  of.  381 
data  for  estimates.  369 

fjravel  vs.  broken-stone.  376 
aying.  379 
mixing.  378 

Portland  vs.  natural  cement,  375 
proportions.  377 

screened  vs.  unscreened  stone,  375 
theory  of  368 

thickness  for  pavement  foundation,  378 
wet  vs.  dry.  376 
Concrete  curb  and  gutter,  353 
Concrete  roads  272 
cost.  356 
double.  357 
finishing.  355 
forms.  354 
foundation,  353 
laying.  355 
merits,  357 
mixing,  355 
private  driveway,  357 
Connecticut  gravel  road,  167 
Corduroy  roads  274 
Creo-resinate   process  of  preserving  wood, 

552 
Creosote  process  of  preserving  wood,  551 
Crops,  cost  of  marketing,  17 
Crossi.igs,  brick.  598 
stones,  621 
cost.  622 
Crown  for  gravel  road.  163 
Crown  of  pavement   328 

amount  in  various  cities,  348 
Crusher,  see  Stone  crusher. 
Culverts,  123 
Curb,  350 
clay.  359 

combined  curb  and  gutter,  353 
concrete.  252 

radius  of,  at  street  corner.  359 
see  also  Concrete  curb  and  gutter, 
stone.  250 
cost.  252 
Curb  with  conduit,  358 
Curves,  horizontal,  in  road,  65 


CUR— EAE 

Curves,  vertical,  at  grade  intersections.  326 
Cushion  coat  for  asphalt  pavement,  401 

Decatur  gravel,  characteristics  of,  156,  157, 

158 
Decomposition    of   stone,    effect    on    stone 

road,  244 
Detroit  road-leveler,  132 
Deval  impact -machine.  183 
Distance  equivalent  to  1  foot  rise  and  fall,  59 
Distance,  value  of  saving,  47 
Distance  vs.  rise  and  fall,  58  ' 
Ditches,  care  of  side.  137 
Dorrey  abrasion  testing-machine,  182 
Dow  penetration  apparatus,  406 
Drainage,  71 

tile,  72 
Drainage  of  pavement  foundation,  360 
Drainage  of  streets.  335 

catch  basins.  336 

gutters,  342 

intersection,  344 

subdrainage,  335 

surface  drainage.  346 
Driveway,  sidewalk  across,  592 
Dust,  oil  as  a  prevention  of,  140 
Dynograph,  Baldwin,  27 

Earth  roads,  care  of  the  surface,  129 
cost  of  maintenance,  141 

scraping,  135 
cross  section.  85.  87,  89 

side-hill.  86 
crown.  84 

examples  of.  85 
definition  of,  71 
destructive  agents,  equal  axles,  128 

horse  before  wheel,  129 

narrow  tires,  126 

small  wheels,  129 

water,  125 
drainage,  71 

side  ditches,  81 

surface,  83 

tile.  72;  see  also  underdrainage  below, 
improving  old,  95 
maintenance  of.  125 

filling  holes.  136 

harrow.  130 

railroad  rail.  130 

removing  stones.  137 

rolling.  136 

scraper.  131 

scraping  grader.  133 
method  of  maintenance,  142 
tile  underdrains.  72 

location  of  78.  80 
tractive  resistance  on,  22,  24,  25,  28,  31 
underdrainage,  72 

fall   75 

object.  72 

tile.  74 
cost,  75 
laying.  77 
cost,  78 
location,  80 
size,  76 
weight,  75 
Earthwork,  balancing  cuts  and  fills.  90 
computing.  90 
cost,  finishing  the  slopes,  122 

in  hard  ground,  116 

labor.  113 

loosening   115 


INDEX. 


bi)l 


EAR-GRA 

Earthwork,  cost  for  various  hauls,  115,  116, 
117,  120 
with  drag-scoop  scraper,  114,  118 
with  elevating  grader,  114 
with  scraping  grader,  113 
with  wagons,  120,  122 
with  wheel  scrapers,  116,  119 
over-haul,  93 
profits  to  contractor,  123 
shrinkage,  91 
Embankments,  rolling,  93 
settlement  of,  92 
side  slope  of,  88 
stability  of,  94 
standard  cross  section  of,  89 
Equestrian  roads,  276 
crown,  276 
drainage,  276 
surface,  277 
width,  276 
European  asphalt,  396 
Excavation,  side  slope  in,  88 
standard  cross  section  in,  89 

Farm  products,  cost  of  marketing.  17 
Felsite  for  broken-stone  roads,  194 
Fences,  artistic,  125 

Field  stones  for  broken-stone  roads,  193 
Flushing,  cross  section  of  road  at.  209 
Foundation  of  pavements,  360,  384 

bituminous  concrete,  383 

gravel,  383 

hydraulic-cement  concrete,  367 

macadam,  382 

plank,  384 
Friction,  axle,  21 

rolling,  21 
Frost,  effect  on  road -stone.  190 

effect  on  stone  road,  244 

Grader,  elevating,  110 
cost  of.  111 
operating,  111 
scraping.  Austin,  102 
Champion.  102 
cost  of,  103 
inclined  wheels.  109 
operating  in  construction,  103 

maintenance.  133 
Shuart.  219         . 
Grades,  effect  of  rise  and  fall,  52 
effect  upon  load,  50 
effect  on  location   50 
Grades  of  pavements,  asphalt,  445 
brick,  515 
broken-stone.  62 
stone-block,  545 
wood-block,  561 
Grades  of  road,  maximum.  60 
as  ascent,  60 
as  descent,  61 

examples,  asphalt  pavement,  445 
bicycle  roads.  63 
earth  roads,  61 
mountain  roads,  63 
on  streets,  63 
pleasure  drives,  63 
stone  roads,  62 
minimum.  63 
vertical  curves,  326 
Grades  of  streets,  318 
at  intersections   322 
elements  governing,  318 

accommodation  of  traffic,  319 


QRA— GUI 

Grades  of   streets,  elements  governing  ap- 
pearance, 319 

cost  of  earthwork,  319 

drainage,  319 

effect  upon  property,  319 
maximum,  320 
minimum,  321 
Granite,  for  broken-stone  roads,  191 

for  paving  blocks,  531 
Granite-block  pavement,  amount  in  U.  SL 

293 
see  Stone-block  pavement, 
tractive  resistance  on,  29 
Gravel,  binder,  147 

materials  of,  148,  150 

requisites  for,  147 
characteristics  of.  154 

Buck  Hill,  156,  157,  159 

Decatur,  156,  157,  158 

Lexington,  156,  157,  158 

Oaktown,  156,  157,  160 

Paducah,  156,  157,  161 

Peekskill,  156,  157,  159 

Rockford,  156.  157,  159 

Rock  Hill.  156.  157.  160 

Rosetta,  156.  157,  161 

Shaker  Prairie.  156,  157.  160 

Shark  River,  156,  157,  160 

Urbana,  155,  156,  157 
cherty,  151 
composition  of,  155 
defined,  146 
distribution  of.  150 
durability,  146 
exploring  for,  153 
foundation  for  pavements  383 
glacial  drift.  150 
hauling,  170 
method  of  loading   170 
method  of  measuring.  171 
mineralogical  analysis  of    157 
requisites  for  road-building.  146 

binder,  147 

durability.  146 

sizes,  147 
screening.  170 
service  test  of.  161 
sieve  analysis  of   156 
sizes  for  road  purposes   147 
Gravel  pavements,  amount  in  U.  S.,  293 
Gravel  road.  146 
bottom  course    169 
Connecticut  standard,  167 
cost.  172 
crown    163 

destructive  agents,  174 
drainage   162 
earth  track  beside   168 
economic  value  of.  172 
forcing  gravel  into  subgrade,  171 
forms  of  construction.  164 

comparisons  of,  168 

surface,  164 

trench   166 
maintenance  cost  of.  176 
repairs  of   175 
rolling    167 
sprinkling.  175 

tractive  resistance  on.  22   24,  25,  28,  3\ 
vs.  broken-stone  road,  173 
Gravel  walk  617 
Guard  rails,  123 
Guide  posts,  124 
Guidet  pavement  defined,  530 


052 


INDEX. 


GUT— OVE 

Gutter,  353 

concrete,  see  Concrete  curb  and  gutter. 

depth,  343 

grade,  344 

material,  342 

St.  Louis  concrete,  353 

Hardness  of  road  stone,  178 

Haul,  average  length  of,  to  market,  13 

Hedges,  care  of,  138 

Horse,  effect  of  grade  on  load  for,  34 
effect  of  grade  on  power  of,  32 
load  for,  on  different  grades,  34 
maximum  load  for,  on  grades,  33 
power  of ,  31 

relative   efficiency  in   America. .and  Eu- 
rope, 9 
relative  efficiency  on  good  and  bad  roads, 
10 

Horses'  feet,  effect  on  stone  road.  242,  245 

Horse-race  track,  see  Race-track,  horse. 

Impact  test  for  road  stone.  181,  182,  186, 

187 
Impact  testing  machine,  183,  188 
Iron  ore  as  road  material,  152 

Jarrah  wood,  description  of,  549 

Karri  wood,  description  of,  549 
Kennet-Square  road-leveler,  132 
Kentucky  asphalt,  396 

Lexington    gravel,   characteristics  of,    156, 

157,  158 
Limestone,  for  broken-stone  roads,  192 

for  paving  blocks.  535 
Load,  average  weight  of,  15 

effect  of  grade  upon.  50 
Location  of  road,  curves,  65 

distance,  effect  of,  46 
value  of  saving.  47 

effect  of  grades,  50 

effect  of  rise  and  fall.  52 

elements  involved,  45 

establishing  grade  line.  70 

grade  maximum.  60 
minimum.  63 

placing  the  line,  67 
Lute  for  cushion  coat  of  pavements  500 

Macadam  for  pavement  foundation.  382 
Macadam  pavement  amount  in  U.  S.,  293 
Macadam  road,  see  Broken-stone  road. 
Macadam,  tractive  resistance  on,  22,  24,  26, 

28,  29,  31 
Macadam  walk,  618 
Market,  average  length  of  haul  to:  13 
Massachusetts  state-aid  roads,  cross  section 

of,  210 
Mud  effect  on  broken-stone  road,  251 

New  York  City,  block- plan.  309 

crown  of  pavements  in   348 
New  York  state-aid  roads,  cross  section  of, 
209 

Oaktown  gravel,  characteristics  of,  156, 157, 

160 
Oil.  preventive  of  dust,  140 
Omaha  crown  of  pavements  in,  348 

plank  sidewalk.  618 
Orton's  method  of  testing  paving  brick,  481 
Over-haul.  93 


PAD-PAV 

Paducah  gravel,  characteristics  of,  156.  157 

161 
Page's  test  of  road-stone,  185 
Park  walks,  617 

Patching  broken-stone  road,  method  of,  252 
Pavements,  amount  in  U.  S.,  293 
Pavements,  annual  cost,  585 
apportionment  of  cost,  296 

in  different  States,  298 
asphalt,  see  Asphalt  pavement, 
assessments  for,  299 
area  rules,  301 
frontage  rule,  300 
legality  of  levy,  302 
terms  of  payment   301 
benefits  of,  295 
brick,  see  Brick  pavement, 
coal-tar,  454 

cost  of  construction,  456 
cost  of  maintenance.  457 
cobble-stone,  see  Cobble-stone  pavement, 
comparisons  of,  563 

amounts  of  different  kinds.  564 
comfort  in  use,  580 
cost,  567,  585 
durability,  567 

comparison  of,  573 
life  of  pavement.  575 
modifying  elements,  572 
traffic.  567 
dust  and  mud,  580 
ease  of  cleaning  579 
healthfulness,  580 
heat  581 
noiselessness,  579 
requirements  of  ideal,  566 
selecting  the  best,  581 
slipperiness,  576 
America,  576 
London. 577 
smoothness,  580 
temperature,  581 
tractive  resistance,  576 
cost,  construction.  584 

maintenance  per  capita,  294 
crown,  328,  346 

in  various  cities,  348 
foundation,  360 

concrete,  bituminous.  383 
hydraulic,  337 
advantages,  368 
thickness,  378 
earthwork.  361 
gravel,  383 
plank,  384 
rolling.  362 
sand,  384 
gravel,  see  Gravel  road, 
guarantee,  302 

macadam,  see  Broken-stone  road, 
maintenance  by  contract,  304 
preparation  of  subgrade,  361 
selecting  the  best,  581 

annual  cost,  importance  of,  585 
conclusion,  588 
ease  of  cleaning,  value  of,  588 
ease  of  traction,  value  of,  587 
first  cost,  importance  of,  583 
foot -hold,  value  of,  588 
other  qualities,  importance  of,  588 
stone-block,  see  Stone-block  pavement, 
tearing  up,  305 
total  cost  in  U.  S.,  293 
width  of,  316 


INDEX. 


653 


PAV— BOA 

Pavements,  width  of,  with  car-tracks,  317 
without  car-tracks,  317 

wood-block,  see  Wood-block  pavement. 
Peekskill  gravel,  characteristics  of,  156  157, 

159 
Penetration  apparatus.  Bowen's.  406 

Dow's,  406 
Plank  foundation  for  pavement,  384 
Plank  road,  274 

tractive  resistance,  29,  31 
Plank  walk,  618 

cost,  620 

Omaha,  619 
Plans  of  street  improvements;  331 
Portland  bicycle  path,  627 
Preserving  timber,  550 

creosote  process,  551 

creo-resinate  process,  552 

kreodone-creosote  process,  552 
Products,  farm,  cost  of  marketing,  17 

Quarrying  cost  of.  234.  235,  237 
Quartzite  for  paving  blocks,  535 

Race-track,  bicycle,  632 
ground  plan,  633 
ideal  form.  637 
curves.  638 

proportions  of  field.  637 
materials.  645 
present  practice.  633 
Charles  River,  634 
Hamoden  Park,  634 
Garfield  Park.  634 
Manhattan  Beach,  634 
Racine.  634 
Race-track,  horse,  278 
drainage,  292 
form,  278 
grades,  291 
kite-shaped.  283 
oval,  standard  half-mile.  281 
standard  mile.  279 
with  easement  curves,  285 
half-mile.  287 
mile,  286 
standard  oval.  279 
half-mile,  281 
mile,  279 
surface.  291 
super-elevation.  288 
Rain,  effect  on  stone  road.  244 
Rattler  for  testing  brick,  Purdue.  485 
standard,  484 
Talbot-Jones,  489 
Raveling,  effect  on  stone  roads,  248 
Retaining  walls.  123 
Right  of  way,  width,  65 
Rise  and  fall,  classes,  53 
cost.  55 
effect.  52 
tar.  distance,  58 
Road  administration,  35 
education  in,  37 
labor  vs.  money  tax,  42 
legislation  vs.  education,  37 
legislative  reform.  37 
otate-aid,  44 
Road-building  machinery,  96 
graders,  elevating,  100 
scraoing.  110 
Shuart.  219 
rollers.  222 
horse  223 


R0A—  R0L 

Road-building    machinery,  rollers,   steam 
224 
scrapers,  97 

drag,  buck,  99 
scoop.  97 

wheel,  100 
Road-leveler,  Detroit,  132 
Kennet-Square,  132 
simple.  132 
Road  roller,  222 
horse,  223 

horse  vs.  steam,  225 
invention  of,  222 
steam,  223 

asphalt.  225.  417 

stone-road,  224 
Road  stone,  method  of  testing.  180 

absorption,  189 

abrasion.  181,  182.  186,  187 

cementation.  185,  186,  187 

crushing,  189 

impact,  181,  182,  186,  187 
requisites  for,  177 
Road  taxes,  39 
cash  tax,  42 
labor  tax,  42 
money  vs.  labor,  42 
poll  tax,  40 
property  tax   40 
toll,  39 
Roads,  advantages  of  good.  3 
artistic  treatment  of,  124 
bad,  estimated  cost  of,  9,  19 
burned-clay,  270 
charcoal,  275 
classification  of,  36 
coal-slack,  273 
coal-tar,  454 
concrete.  272 
corduroy.  274 
cost  of.  41 

earth,  see  Earth  road, 
equestrian,  see  Equestrian  roads, 
financial  value  of  improved,  8,  19 
good,  effect  of,  on  price  of  land,  5 
improving  old,  95 
location  of.  45 
plank,  274 

sand,  see  Sand  roads, 
shade  on.  124 
shell,  272 
slag.  273 

social  benefits  of  good,  5 
state-aid,  44 
steel,  264 
trees  on,  124 
width  of  wheelway,  87 

see  also  Right  of  way. 
Roadside,  care  of.  138 
Rockford  gravel,    characteristics    of,    156 

157.  159 
Rock   Hill   gravel,  characteristics  of,   156 

157.  160 
Roller,  223 

asphalt.  225,  417 
horse,  223 
steam,  223 
Rolling,  asphalt  pavements,  416,  419 
brick  pavements,  505 
broken-stone  roads.  226 
effect  on  maintenance  of  stone  road,  250 
embankments.  93 
resistance.  21 
gravel  roads,  167 


654 


INDEX. 


BOL—  SID 

Rolling,  stone  roads,  226 

subgrade  of  pavement,  362 
Roman  roads,  description,  528 
Rosetta  gravel,  characteristics  of,  156,  157, 

161 
Rubble  pavement,  definition,  529 
Rumbling  of  brick  pavements,  511 
Russ  pavement,  description.  529 
Ruts,  removing  from  stone  road,  249 

Sand  for  pavement  foundation,  384 
Sand  roads,  144 

drainage.  144 

effect  of  shade  on,  144 

grading,  144 

hardening  the  surface.  144 

tractive  resistance  on.  25.  31 
Sandstone  for  broken-stone  roads,  193 

for  paving  blocks,  533 
Scrapers,  97 

d  rag  scoop,  97 

Fresno,  99 

tongue.  98 

wheel.  100 
Scraping  grader,  see  Grader. 
Settlement  of  embankments.  92 
Shale  for  broken-stone  roads,  194 
Shaker    Prairie    gravel,   characteristics   of, 

156.  157.  160 

Shark  River  gravel,  characteristics  of,  156, 

157,  160 
Shell  roads,  272 
Shrinkage  of  earth,  91 
Shuart  grader.  219 
Sidewalks,  590 

across  private  driveway,  592 
asphalt,  592 

block,  593 

sheet.  593 
brick,  593 

bricks,  594 

direction  of  rows,  596 
laying,  597 

cost,  601 

crossings,  paved  street,  598 
unpaved  street,  599 

foundation,  594 

merits  and  defects.  602 

transverse  slope.  598 
cement,  602 

across  drivewav,  614 

base,  603 

Portland  vs.  natural,  610 

color.  611 

cost.  615 
labor,  615 
materials,  615 

expansion.  609 

forms.  603 

foundation.  602 

joints.  607 

precautions.  613 

slipperiness,  613 

street  signs,  612 

transverse  slope.  610 

wearing  coat,  604 
cinder.  616 
comparisons  of,  623 
crossing  stones,  621 
grade  of,  591 
gravel.  617 
location  of,  590 
macadam.  618 
plank.  618 


SID— STB 

Sidewalks,  plank,  cost  of,  620 
stone.  620 
cost  of,  622 
crossing  stones,  621 
cost  of,  622 
tar,  623 

transverse  slope  of.  591 
width  of,  591 
Slag  roads,  273 

Slate  for  broken-stone  roads,  194 
Slope-stakes,  setting.  90 
Snow,  cost  of  clearing,  139 

obstruction  by,  138 
Specifications  for  street  improvements.  331 
Sprinkling  stone  roads,  during  construction, 
231 
effect  on  maintenance.  250 
State  aid.  Connecticut,  44 
Massachusetts,  44 
New  Jersey,  44 
New  York,  44 
Stone,  road-building,  characteristics  of  v  190 
distribution  of.  190,  195 
requisites  for.  177 
Stone-block  pavement,  528 
construction.  536 
blocks.  537 
dressing.  537 
size.  538 
setting.  542 
filling  joints.  543 
cement,  544 
sand,  544 
tar.  544 
foundation.  536 
ramming.  543 
sand  cushion,  536 
cost.  545 

blocks  at  Quincy,  546 
Chicago,  546 
Liverpool,  547 
New  York  city.  546 
Rochester,  N.  Y..  547 
crown  for.  in  various  cities,  348 
grade,  maximum,  545 
hammer,  542 
kinds.  Belgian  block,  529 
Guidet  block,  530 
Roman  roads.  528 
Russ  patent,  529 
rubble,  529 
standard.  530 
merits  and  defects,  545 
rammer,  543 
stone,  granite.  531 
limestone,  535 
sandstone.  533 
Kettle  River,  535 
Medina,  534 
Potsdam.  534 
Sioux  Falls,  535 
tractive  resistance  of.  26,  28,  29,  31 
Stone-block  rammer,  543 
Stone  crushers.  214 
gyratory,  215 
oscillatory,  214 
Stone-paving  hammer.  542 
Street,  cross  section  of  side-hill.  328 
design,  307 
drainage.  335 

catch  basins,  336 
gutters.  342 
intersection.  344 
subdrainage.  335 


INDEX. 


655 


STR-TRA 

Street  drainage,  surface  drainage,  346 
grades,  see  Grades, 
intersection,  drainage  at.  344 
plan,  307 

blocks,  size  of,  308 

lots,  size  of.  308 

streets,  arrangement  of,  312 

checkerboard,  312 
diagonal.  312' 

concentric,  314 
area  of.  315 
location  of,  310 

with  reference  to  contours.  310 
with    reference    to    ease    of  com- 
munication, 312 
width,  314 
signs  in  cement  walk,  612 
trees,  332 
Streets,  area  of.  in  various  cities,  315 
location  of.  310 

with  reference  to  contours,  310 
with  reference  to  communication,  312 
width,  314 
Swiss  roads,  cross  section  of.  210 
Switzerland,  cross  section  of  road  in,  210 

Talbot's  method  of  testing  paving  brick, 

481 
Talbot-Jones    method    of    testing    paving 

brick.  488 
Tar,  459 

cost,  460 

macadam,  458 
construction.  459 
cost.  460 

merits  and  defects,  460 
the  tar,  459 

pavements,  see  Coal-tar  pavements. 

walks,  see  Sidewalks. 
Telford,  cost  of  setting.  236 

method  of  setting.  212 
Telford  road.  177.  195,  196 
Template  for  brick  pavement,  499 
Texas  asphalt,  396 
Tile,  cost,  76 

drainage.  74 

formula  for  size  of,  76 

weight.  75 
Tires,  effect  of  narrow,  126 

width  of.  effect  on  rolling  resistance.  23, 
24.  25 
Toughness  of  road  stone.  178 
Tracking,  effect  on  stone  road,  243 
Trackway,  see  Wheel  way. 
Traction,  resistance  of,  21 

asphalt.  29.  31 

brick.  29.  31 

data  on,  22.  24.  25,  26.  28,  29   31 

definition  of,  21 

earth  roads.  22.  24.  25   28.  31 

effect  of  diameter  of  wheel,  22 

effect  of  grade,  30 

effect  of  speed,  26 

effect  of  width  of  tire.  23.  24,  25 

plank.  29.  31 

steel  wheelwav,  29   31 

stone  block.  26.  2<S.  29.  31 

wood  block,  25,  29,  31 
Traffic,  census  of.  567 

Canada. 571 

England.  571 

United  States.  567 


TRA— WOO 

Tramway,  see  Wheel  way. 
Transportation,  cost  of  wagon,  6 
to  farmers,  7,  16 
to  freighters.  6 

data  on  cost  of  wagon.  11,  13,  15 
Trap,  for  broken-stone  roads.  191 
Trees,  care  of  on  roadside,  124.  138 

on  streets.  332 
Trenches,  filling  of,  363 

flooding.  364 

natural  settlement,  364 

replacing  all  the  material,  366 

tamping,  365 

using  sand  or  concrete,  367 
Trinidad  asphalt,  391 

Urbana,  gravel,  characteristics  of,  155,  156 

157 
Utah  asphalt,  396 

Wragons.  economic  number  of  men  to  load, 

113.  121 
Walks,  see  Sidewalks. 
Washington,  street-plan  of,  313 
Water,  destructive  effect  on  roads,  125 
Waterways,  123 

Wheel,  effect  of  diameter  on  tractive  re- 
sistance, 22 
effect  on  macadam  road,  242,  245 
effect  of  small,  on  roads.  129 
Wheelwavs.  263 
brick.  270 
clay-block,  270 
steel.  264 

advantages.  266 
construction.  265 
disadvantages.  268 
tractive  resistance,  29,  31 
stone.  263 
Width  of  right  of  way,  65 
Wind,  effect  on  stone  road.  243 
Wings  for  broken-stone  road,  208 
Wood-block  pavements    amount  in  U.  S.. 
293 
crown  for,  in  various  cities.  348 
foundation,  554 
history,  549 
rectangular-block,  557 
blocks.  558 

placing.  558 
cost.  561 
expansion,  559 
foundation,  557 
grades.  561 
joints,  filling,  559 
repairs,  560 
round-block,  554 
blocks,  555 
cost .  557 
foundation,  554 
laying,  556 
tractive  resistance  of.  25,  29,  31 
wood,  Jairah,  549 
Karri,  549 
preserving  550 
creosoting.  551 
creo-resinate  process  552 
kreodone-creosote  process,  552 
quality  of,  550 
value  of  preserving,  553 
varieties  of.  549 


A    TREATISE 

ON 

ROADS  AND  PAVEMENTS. 

By  IRA  O.  BAKER,  C.  E.,  D.  Eng  g. 

Prof essor  of  Civil  Engineering,  University  of  Illinois;  Member  American  Society 
of  Civil  Engineers,  etc.;    Author  of  a  Treatise  on  Masonry  Construction,  etc. 

Cloth,  6X9  inches,  viii-f-655  pages;  171  figures;  68  tables  of  dimensions, 
cost,  etc.     Extensive  analytical  index. 

SUMMARY  OF  CO  1ST  TENTS. 
Part  I.  COUNTRY  ROADS.  Chap.  I.  Road  Economics— advantages  of 
good  roads,  cost  of  wagon  transportation,  tractive  resistance,  road  administration,  road 
taxes,  State  aid.  Chap.  II.  Road  Location — relative  cost  of  distance,  grade,  and 
rise  and  fall;  width,  curves,  cross  section.  Chap.  III.  Earth  Roads — construction: 
surface  and  under  drainage,  crown,  width  of  wheelway,  cost;  road-building  machinery: 
scrapers,  scraping  grader,  elevating  grader;  maintenance:  methods,  cost.  Chap.  IV. 
Gravel  Roads — the  gravel:  requisites  for  road  gravel,  distribution  of  gravel,  method 
of  exploring  for  gravel;  construction:  drainage,  crown,  forms  of  gravel  roads,  cost, 
gravel  vs.  earth  roads;  maintenance:  methods,  cost.  Chap.  V.  Broken=Stone 
Roads — the  stone:  requisites  of  road  stone,  method  of  testing;  construction:  telford, 
macadam,  thickness,  crown,  crushing  the  stone,  rolling,  binding,  cost,-  maintenance: 
amount  and  cause  of  wear,  methods  of  repair,  cost,  economics  of  broken-stone  roads. 
Chap.  VI.  Miscellaneous  Roads — steel  and  stone  wheelways,  burned-clay  roads, 
shell  roads,  etc.    Chap.  VII.  Equestrian  Roads  and  Horse-Race  Tracks. 

Part  II.  STREET  PAVEMENTS.  Chap.  VIII.  Pavement  Economics- 
apportionment  of  cost,  special  assessments,  tearing  up  pavements.  Chap.  IX.  Street 
Design — street  plan,  width  of  streets,  width  of  pavement,  grade,  crown  of  pavement, 
cross  section  of  side- hill  streets,  street  trees.  Chap.  X.  Street  Drainage — drainage, 
catch  basins,  gutters.  Chap.  XL  Curbs  and  Gutters.  Chap.  XII.  Pavement 
Foundations — subgrade:  drainage,  rolling,  filling  trenches;  foundations:  concrete, 
gravel,  macadam,  plank,  etc.  Chap.  XIII.  Asphalt  Pavement — the  asphalt: 
characteristics,  composition,  properties;  sheet-asphalt  pavement:  foundation,  binder 
course,  wearing  coat,  permissible  grade,  causes  of  failure,  methods  of  repair,  cost;  rock- 
asphalt  pavement;  asphalt-block  pavement;  asphalt-macadam;  coal-tar  pavements. 
Chap.  XIV.  Brick  Pavement — requisites  of  paving,  testing  the  brick,  laying  the 
brick,  joint  filler,  permissible  grade,  rumbling,  cost.  Chap.  XV.  Cobble-Stone 
Pavement.  Chap.  XVI.  Stone= Block  Pavement — the  stone:  requisites,  size, 
form,  cost;  construction:  foundation,  setting  the  blocks,  filling  joints,  permissible  grade, 
cost.  Chap.  XVII.  Wood-Block  Pavement — preserving  the  wood,  round-block, 
square-block  pavement,  foundation,  filling  joints,  permissible  grade,  cost.  Chap.  XVIII. 
Comparison  of  pavements — requirements  of  an  ideal  pavement,  method  of  selecting 
the  best  pavement.  Chap.  •  XIX.  Sidewalks — asphalt,  brick,  cement,  gravel, 
macadam,  plank,  stone.     Chap.  XX.  Bicycle  Paths  and  Race  Tracks. 

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JOHN  WILEY  <&  SONS.  «^  V^SS^^f™™' 


OPINION  OF  THE  PRESS. 


"  The  task  Professor  Baker  has  set  before  himself  is  not  a  simple  one,  as  the  subject 
is  complex  and  calls  for  a  considerable  amount  of  discussion  of  detail;  but  every  point 
has  received  adequate  treatment,  and  the  result  is  the  production  of  a  volume  of  great 
usefulness  and  of  outstanding  merit.  The  author  is  an  American,  and  the  book  deals 
primarily  with  the  conditions  met  with  in  America;  but  practically  the  whole  contents 
are  as  applicable  in  Great  Britain  and  in  Europe  generally  as  in  the  United  States,  and 
we  have  no  hesitation  in  recommending  the  work  to  British  engineers.  Part  I  is  devoted 
to  country  roads,  and  opens  with  a  very  interesting  chapter  on  road  economics.  It  would 
be  very  easy  for  any  one  who  has  an  axe  to  grind  to  make  out  a  highly  satisfactory  case 
in  dealing  with  this  phase  of  the  subject,  but  the  author  has  not  adopted  a  partisan  atti- 
tude. We  particularly  recommend  careful  consideration  of  the  author's  remarks  in 
Chapter  II,  and  again  later  in  the  volume,  in  discussing  grades,  on  the  effect  of  saving 
distances,  and  the  elements  to  be  considered  in  that  connection.  *  *  *  In  Part  II  we  are 
brought  to  city  streets,  where  good  construction  is  still  more  important  than  in  country 
roads,  for  the  sanitary  aspect  of  the  question  becomes  prominent  and  the  traffic  to  be 
borne  is  much  heavier.  In  this  section  of  the  work  a  chapter  on  economics  of  the  subject 
again  serves  as  an  introduction  to  the  discussion  in  detail,  and  it  is  followed  by  a  valuable 
chapter  on  street  design.  The  ahthor  has  dealt  with  street-paving  in  a  comprehensive 
and  thoroughly  scientific  manner,  discussing  the  construction  of  asphalt,  brick,  cobble- 
stone, stone-block,  and  wood-block  pavements  in  detail,  and  comparing  their  advantages 
in  point  of  cost,  sanitary  qualities,  and  general  acceptability.  Professor  Baker  deserves 
great  praise  for  the  thoroughness  with  which  he  has  treated  a  most  important  branch  of 
engineering,  and  we  commend  his  work  to  all  who  have  any  connection  with,  or  interest 
in,  the  construction  of  good  roads  and  streets.  The  volume  has  a  good  appearance,  and 
the  type  and  illustrations  are  excellent." — Engineering,  London. 

"  Professor  Baker  has  well  sustained  the  reputation  gained  by  his  book  on  *  Masonry 
Construction.'  There  have  been  several  excellent  books  on  the  general  subjects  em- 
braced in  the  title  of  this  book,  which  have  appeared  recently,  some  of  which  have  treated 
particular  parts  of  the  field  more  thoroughly  and  completely  than  this  book,  but  none 
give  so  complete  a  survey  of  the  entire  subject.  A  number  of  chapters  are  upon  topics 
never  before  properly  treated  in  a  book.  *  *  *  As  a  whole  the  book  is  the  most  com- 
prehensive treatment  of  its  subject  which  has  appeared  and  will  undoubtedly  take  its  place 
as  the  basis  for  any  detailed  study  of  pavements.  It  contains  the  results  of  a  number  of 
valuable  experiments  made  by  and  under  the  direction  of  the  author,  and  makes  some 
positive  and  original  additions  to  the  knowledge  of  the  world  on  this  subject." — Mu- 
nicipal Engineering,  Indianapolis. 

"This  latest  treatise  on  roads  and  pavements  is  written  in  a  clear  and  concise  style, 
and  great  care  has  evidently  been  taken  to  secure  a  logical  development  of  the  several 
subjects.  The  typographical  arrangement  of  titles  and  headings  facilitate  quick 
and  easy  reference.  The  volume  contains  many  tables  which  are  carefully  arranged 
and  are  self-explanatory.  It  is  probably  the  best  American  text-book  for  students,  and 
contains  material  that  should  be  helpful  to  every  practical  road-builder." — Good  Roads 
Magazine,  New  York  City. 

"  Professor  Baker  has  followed  closely  the  arrangement  adopted  by  him  in  his 
Treatise  on  Masonry  Construction,  the  volume  being  divided  into  parts,  chapters,  articles 
and  sections,  thus  making  it  easy  to  refer  to  any  particular  subject.  The  book  is  well 
illustrated  and  has  many  specifications  and  tables  of  costs." — Engineering  Record, 
New  York  City. 

M  This  work  is  a  notable  addition  to  the  literature  of  roads  and  pavements.  The 
treatment  of  the  vexed  question  of  the  economic  value  of  good  country  roads,  while  brief, 
is  particularly  full  and  complete.  While  an  avowed  friend  of  good  reads,  Professor  Baker 
evidently  feels  that  the  good  cause  is  more  likely  to  be  injured  than  benefited  by  exagger- 


ated  claims  and  unverified  statements  of  the  financial  and  industrial  benefits  that  follow 
the  building  of  improved  highways  and  that  in  the  end  their  promotion  is  sure  to  be  con- 
served  by  the  ascertainment  and  publication  of  the  exact  truth,  as  nearly  as  it  is  attainable. 
His  conclusion  will  not,  of  course,  meet  the  approval  of  these  over-enthusiasts,  not  a  few 
of  whom  would  have  us  believe  that  the  economic  and  social  salvation  of  the  country  must 
come  largely  along  improved  highways.  It  may  be  confidently  predicted  that  the  mod- 
erate views  presented  by  the  author  will  in  time  be  substantially  confirmed  and  approved 
by  the  sober  second  thought  of  the  best  friends  of  the  good-roads  movement.  The  chapter 
on  Equestrian  Roads  and  Horse-Race  Tracks  will  be  welcomed  by  the  engineer  who 
may  have  occasion  to  lay  out  and  construct  roads  of  this  kind.  The  author's  treatment 
of  the  large  subject  of  street  pavement  is  logical  in  arrangement  and  terse  and  clear  in 
diction,  and  embraces  all  the  material  facts  available  upon  the  subject.  The  chapter  on 
the  relative  value  and  desirability  of  the  several  varieties  of  pavement  and  suggested 
methods  of  choosing  for  each  locality  and  set  of  conditions,  the  pavement  best  suited  to 
the  purpose,  is  characterized  by  such  a  fair  and  judicial  statement  of  the  facts  as  should 
give  weight  to  the  conclusions  reached.  Perhaps  the  time  may  come  when  city  authorities 
and  urban  citizens  will  pursue  a  similar  reasoning  in  selecting  for  each  street  the  pave- 
ment that  will  best  meet  the  requirements  under  the  conditions  that  exist.  As  a  whole, 
the  book  is  a  most  creditable  production,  and  it  can  not  fail  to  add  to  the  already  high 
reputation  of  Professor  Baker  as  a  writer  upon  engineering  subjects." — Railroad 
Gazette,  New  York  City. 

"  The  most  valuable  part  of  the  first  chapter,  and  in  fact  the  most  original  part  of  the 
book,  is  the  author's  contribution  to  the  knowledge  of  tractive  resistances  on  various 
pavements.  The  author  gives  data  based  on  his  own  experiments,  and  he  has  also  com- 
piled in  tabular  form  most  of  the  previously  published  data  of  others.  These  compilations, 
together  with  the  original  matter,  form  a  more  satisfactory  treatment  of  traction  than 
exists  in  any  other  manual.  *  *  *  The  chapter  on  brick  pavements  is  more  satisfactory 
than  that  in  any  other  book  we  have  seen ;  in  fact,  it  is  one  of  the  best  chapters  in  the 
book.  *  *  *  Chapters  on  race  tracks,  both  for  horses  and  bicycles,  contain  matter  not  to  be 
found  in  other  road  books,  and  the  same  may  be  said  of  bicycle  paths." — Engineering 
News,  New  York  City. 

"We  believe  the  work  of  the  author  extremely  well  done.  We  also  believe  that 
enough  new  matter  and  new  ideas  have  been  introduced  fully  to  warrant  this  addition 
to  the  already  large  number  of  similar  works  devoted  to  this  general  subject.  Especially 
admirable  is  the  arrangement  of  chapters.  This  arrangement  gives  the  table  of  con- 
tents unusual  value,  enabling  the  reader  at  a  glance  to  observe  both  the  presence  and 
absence  of  the  matter  sought.  *  *  *  While  the  work  will  greatly  aid  the  builders 
of  city  streets,  we  believe  it  will  especially  commend  itself  to  that  larger  body  of  intelli- 
gent men  who  are  at  this  time  interested  in  the  improvement  of  country  roads,  and  to 
them  we  commend  its  careful  perusal." — Science,  "New  York  City. 

"  In  this  volume  of  650  pages  the  author  has  produced  the  most  thorough  and 
practical  book  on  the  making  of  country  roads  and  city  pavements  that  has  thus  far 
appeared  in  the  United  States.  *  *  *  Professor  Baker's  work  can  not  be  too  highly 
commended  for  its  judicial  tone,  its  comprehensive  knowledge,  and  its  practical  help- 
fulness. The  volume  is  liberally  illustrated  with  cuts  and  diagrams." — Record- 
Herald,  Chicago. 

"  The  tables,  the  estimates,  the  discussion  of  materials  and  methods,  the  designs 
and  illustrations  are  all  comprehensive  and  are  just  what  are  needed  by  the  people  in 
order  to  understand  what  to  do  and  how  to  do  it  in  order  to  improve  their  condition 
as  respects  the  public  highways.  Not  the  least  valuable  part  of  the  book  is  the  splendid 
index,  which  enables  the  reader  quickly  to  discover  the  whereabouts  of  any  particular 
information  he  is  seeking." — Farmer's  Voice.  Chicago. 

"The  book  takes  its  place  at  once  as  the  standard,  and  becomes  absolutely  indis- 
pensable to  every  municipal  engineer  and  road  supervisor.  It  treats  of  every  possible 
branch  of  road-building  and  street-paving." — Stone,  Chicago. 


OTHER  WORKS  OF 

Prof.  IRA  O.  BAKER. 


A  Treatise  on   Masonry   Construction. 

Tenth  Edition.  Entirely  re-written  and  greatly  enlarged.  Cloth,  6X9  inches, 
745 +  xv  pages;  244  figures,  many  of  which  are  full  page;  100  tables  of  cost,  strength, 
etc.     Copious  index.     Price,  $5.00. 

Numerous  changes  and  additions  have  been  made  throughout  the  book,  particu- 
larly in  the  chapter  on  Plain  Concrete  and  in  the  three  new  chapters  on  Reinforced 
Concrete,  Concrete  Building-Blocks,  and  Elastic  Arch,  and  also  in  connection  with 
the  new  structures  illustrated.  There  is  35  per  cent  more  matter  in  this  than  in  the 
preceding  edition. 

"When  the  first  edition  of  this  well-known  work  was  published,  we  expressed  the 
opinion  that  it  was  the  most  valuable  and  complete  treatise  on  Masonry  as  yet  pub- 
lished, at  least  in  English."  *  *  *  "  After  a  careful  inspection  of  the  tenth  edition 
we  see  no  reason  to  amend  the  opinion  expressed  above.  The  book  is  still  the  most 
valuable  and  complete  treatise  on  masonry  as  yet  published." — Engineering  News, 
New  York  City. 

"The  new  edition  well  merits  a  still  greater  popularity  than  that  already  enjoyed 
by  the  previous  ones." — Journal  Western  Society  of  Engineers,  Chicago. 

"Professor  Baker  has  supplied  us  just  at  the  right  time  with  just  the  book  which 
architects  and  engineers  have,  perhaps,  needed  more  than  any  other — a  modern  treatise 
on  constructions  of  stone,  brick  and  mortar.  *  *  *  It  would  be  hard  to  find  anything 
of  importance  in  the  bock  to  which  exception  could  be  taken." — American  Architect, 
Boston. 

"Those  who  know  this  splendid  work  need  not  be  told  that  it  is  free  from  padding. 
It  is  a  plain,  useful  engineering  guide  within  the  department  indicated  by  its  title. 
There  is  no  other  book  which  so  adequately  covers  this  field." — Mining  and  Scientific 
Press.  

Engineers'   Surveying  Instruments. 

Their  Construction,  Adjustment,  and  Use.  Second  Edition,  Revised  and  Greatly 
Enlarged.     i2mo,  ix-f- 391  pages,  86  figures.     Cloth,  $3.00. 

"We  are  pleased  to  see  a  book  of  this  character  appear.  *  *  *  We  recommend 
Professor  Baker's  book  also  for  the  clearness  and  conciseness  with  which  it  is  written. 
It  contains  much  serviceable  matter  to  the  student  and  to  the  practitioner,  well 
expressed." — Journal  of  the  Franklin  Institute,  Thiladelphia. 

14  It  is  up  to  date;  it  is  full  of  sound  practical  hints  which  did  not  come  from  other 
books,  but  were  personally  gathered;  it  gives  plentiful  records  of  the  results  of  actual 
experience.  It  is  also  more  than  its  name  implies.  It  is  not  merely  nor  chiefly  a 
treatise  on  the  anatomy  of  field  instruments;  it  is  rather  a  Manual  of  Instrumental 
Field-work.  *  *  *  The  copious  notes  scattered  through  the  volume,  on  the  degree  ot 
precision  attained  in  practice,  by  various  ways  of  using  the  various  instruments,  are 
alone  of  great  value  and  interest." — Engineering  News,  New  York  City. 


PUBLISHED   AND    FOR    SALE    BY 

JOHN  WILEY  ®.  SONS,  ~*»  enETevtoerekntc7tvstreet' 


Short-title  Catalogue 

OF    THE 

PUBLICATIONS 

OF 

JOHN  WILEY   &  SONS 

New  York 

London:   CHAPMAN    &  HALL,  Limited 


ARRANGED    UNDER   SUBJECTS 


Descriptive  circulars  sent  on  application.     Books  marked  with  an  asterisk  (*)  are 
sold  at  net  orices  only.      All  books  are  bound  in  cloth  unless  otherwise  stated. 


AGRICULTURE— HORTICULTURE— FORESTRY. 

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*  Bowman's  Forest  Physiography 8vo,  5  00 

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Elliott's  Engineering  for  Land  Drainage 12mo,  2  t>0 

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1 


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2 


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24mo,  leather, 

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ASSAYING. 

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Gerhard's  Guide  to  Sanitary  Inspections 12mo, 

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Hazen's  Clean  Water  and  How  to  Get  It Large  12mo, 

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*  Kinnicutt,  Winslow  and  Pratt's  Sewage  Disposal 8vo, 

Leach's  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

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*  Mast's  Light  and  the  Behavior  of  Organisms Large  12mo, 

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*  Merriman's  Elements  of  Sanitary  Engineering 8vo,  $2  00 

Ogden's  Sewer  Construction 8vo,  3  00 

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Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 
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